explanation blue bibcodes open ADS page with paths to full text
Author name code: vlahos
ADS astronomy entries on 2022-09-14
author:"Vlahos, Loukas"
---------------------------------------------------------
Title: Magnetic field spectral evolution in the inner heliosphere
Authors: Sioulas, Nikos; Huang, Zesen; Shi, Chen; Velli, Marco;
Tenerani, Anna; Vlahos, Loukas; Bowen, Trevor A.; Bale, Stuart D.;
Bonnell, J. W.; Harvey, P. R.; Larson, Davin; Pulupa, arc; Livi,
Roberto; Woodham, L. D.; Horbury, T. S.; Stevens, Michael L.; Dudok
de Wit, T.; MacDowall, R. J.; Malaspina, David M.; Goetz, K.; Huang,
Jia; Kasper, Justin; Owen, Christopher J.; Maksimović, Milan; Louarn,
P.; Fedorov, A.
2022arXiv220902451S Altcode:
The radial evolution of the magnetic field fluctuations spectral
index and its dependence on plasma parameters is investigated using
a merged Parker Solar Probe ($PSP$) and Solar Orbiter ($SO$) dataset
covering heliocentric distances between $0.06 ~ \lesssim R ~\lesssim
1$ au. The spectrum is studied as a function of scale, normalized to
the radially dependent ion inertial scale $d_{i}$. In the vicinity of
the Sun, the magnetic spectrum inertial range is limited with a power
law exponent $\alpha_{B}$ consistent with the Iroshnikov-Kraichman
phenomenology of Alfvénic turbulence, $\alpha_{B} = -3/2$, independent
of plasma parameters. The inertial range of turbulence grows with
distance from the Sun, progressively extending to larger spatial
scales, while at the same time steepening towards a Kolomogorov
scaling, with a mean value of $\alpha_{B} =-5/3$. Highly alfvénic
intervals seem to retain their near-Sun scaling and only show a minor
steepening with distance. In contrast, intervals, where turbulence
is characterized by large magnetic energy excess and no dominance of
outwardly propagating Alfvénic fluctuations, appear to have spectra
that steepen significantly with distance from the Sun, resulting in
slightly anomalously steep inertial range slopes at $1~au$. Though
generically slower solar wind streams exhibit steeper spectra, the
correlation can be attributed to the underlying positive correlation
between solar wind speed and alfvénicity, i.e. to the relatively rare
occurrence of highly Alfvénic slow wind.
---------------------------------------------------------
Title: Magnetic Field Intermittency in the Solar Wind: Parker Solar
Probe and SolO Observations Ranging from the Alfvén Region up to 1 AU
Authors: Sioulas, Nikos; Huang, Zesen; Velli, Marco; Chhiber, Rohit;
Cuesta, Manuel E.; Shi, Chen; Matthaeus, William H.; Bandyopadhyay,
Riddhi; Vlahos, Loukas; Bowen, Trevor A.; Qudsi, Ramiz A.; Bale,
Stuart D.; Owen, Christopher J.; Louarn, P.; Fedorov, A.; Maksimović,
Milan; Stevens, Michael L.; Case, Anthony; Kasper, Justin; Larson,
Davin; Pulupa, Marc; Livi, Roberto
2022ApJ...934..143S Altcode: 2022arXiv220600871S
Parker Solar Probe (PSP) and SolO data are utilized to investigate
magnetic field intermittency in the solar wind (SW). Small-scale
intermittency (20-100 d <SUB> i </SUB>) is observed to radially
strengthen when methods relying on higher-order moments are considered
(SF<SUB> q </SUB>; SDK), but no clear trend is observed at larger
scales. However, lower-order moment-based methods (e.g., partial
variance of increments; PVI) are deemed more appropriate for examining
the evolution of the bulk of coherent structures (CSs), PVI ≥ 3. Using
PVI, we observe a scale-dependent evolution in the fraction of the data
set occupied by CSs, f <SUB>PVI≥3</SUB>. Specifically, regardless
of the SW speed, a subtle increase is found in f <SUB>PVI≥3</SUB>
for ℓ = 20 d <SUB> i </SUB>, in contrast to a more pronounced radial
increase in CSs observed at larger scales. Intermittency is investigated
in relation to plasma parameters. Though, slower SW speed intervals
exhibit higher f <SUB>PVI≥6</SUB> and higher kurtosis maxima, no
statistical differences are observed for f <SUB>PVI≥3</SUB>. Highly
Alfvénic intervals display lower levels of intermittency. The
anisotropy with respect to the angle between the magnetic field
and SW flow, Θ<SUB>VB</SUB> is investigated. Intermittency is
weaker at Θ<SUB>VB</SUB> ≍ 0° and is strengthened at larger
angles. Considering the evolution at a constant alignment angle, a
weakening of intermittency is observed with increasing advection time
of the SW. Our results indicate that the strengthening of intermittency
in the inner heliosphere is driven by the increase in comparatively
highly intermittent perpendicular intervals sampled by the probes with
increasing distance, an effect related directly to the evolution of
the Parker spiral.
---------------------------------------------------------
Title: Statistical Analysis of Intermittency and its Association
with Proton Heating in the Near-Sun Environment
Authors: Sioulas, Nikos; Velli, Marco; Chhiber, Rohit; Vlahos, Loukas;
Matthaeus, William H.; Bandyopadhyay, Riddhi; Cuesta, Manuel E.; Shi,
Chen; Bowen, Trevor A.; Qudsi, Ramiz A.; Stevens, Michael L.; Bale,
Stuart D.
2022ApJ...927..140S Altcode: 2022arXiv220110067S
We use data from the first six encounters of the Parker Solar Probe
and employ the partial variance of increments (PVI) method to study the
statistical properties of coherent structures in the inner heliosphere
with the aim of exploring physical connections between magnetic field
intermittency and observable consequences such as plasma heating and
turbulence dissipation. Our results support proton heating localized
in the vicinity of, and strongly correlated with, magnetic structures
characterized by PVI ≥ 1. We show that, on average, such events
constitute ≍19% of the data set, though variations may occur depending
on the plasma parameters. We show that the waiting time distribution
(WT) of identified events is consistent across all six encounters
following a power-law scaling at lower WTs. This result indicates that
coherent structures are not evenly distributed in the solar wind but
rather tend to be tightly correlated and form clusters. We observe
that the strongest magnetic discontinuities, PVI ≥ 6, usually
associated with reconnection exhausts, are sites where magnetic
energy is locally dissipated in proton heating and are associated
with the most abrupt changes in proton temperature. However, due to
the scarcity of such events, their relative contribution to energy
dissipation is minor. Taking clustering effects into consideration,
we show that smaller scale, more frequent structures with PVI between
1 ≲ PVI ≲ 6 play a major role in magnetic energy dissipation. The
number density of such events is strongly associated with the global
solar wind temperature, with denser intervals being associated with
higher T <SUB> p </SUB>.
---------------------------------------------------------
Title: Particle heating and acceleration by reconnecting and
nonreconnecting current sheets
Authors: Sioulas, Nikos; Isliker, Heinz; Vlahos, Loukas
2022A&A...657A...8S Altcode: 2021arXiv210708314S
In this article, we study the physics of charged particle energization
inside a strongly turbulent plasma, where current sheets naturally
appear in evolving large-scale magnetic topologies, but they are
split into two populations of fractally distributed reconnecting and
nonreconnecting current sheets (CS). In particular, we implemented
a Monte Carlo simulation to analyze the effects of the fractality
and we study how the synergy of energization at reconnecting CSs
and at nonreconnecting CSs affects the heating, the power-law high
energy tail, the escape time, and the acceleration time of electrons
and ions. The reconnecting current sheets systematically accelerate
particles and play a key role in the formation of the power-law tail in
energy distributions. On the other hand, the stochastic energization
of particles through their interaction with nonreconnecting CSs can
account for the heating of the solar corona and the impulsive heating
during solar flares. The combination of the two acceleration mechanisms
(stochastic and systematic), commonly present in many explosive events
of various sizes, influences the steady-state energy distribution,
as well as the transport properties of the particles in position- and
energy-space. Our results also suggest that the heating and acceleration
characteristics of ions and electrons are similar, the only difference
being the time scales required to reach a steady state.
---------------------------------------------------------
Title: Statistical analysis of intermittent structures and their
implications on heating during the first six PSP encounters.
Authors: Sioulas, Nikos; Velli, Marco; Matthaeus, William; Vlahos,
Loukas; Qudsi, Ramiz; Chhiber, Rohit; Bandyopadhyay, Riddhi; Bowen,
Trevor; Stevens, Michael; Bale, Stuart
2021AGUFMSH35C2098S Altcode:
We use high-resolution Parker Solar Probe data from the first six
encounters to study the statistical properties of intermittent,
coherent structures and investigate the physical connections between
magnetic field intermittency and observable consequences such as solar
wind dissipation and plasma heating. More specifically, the Partial
Variance of Increments (PVI) method is employed to estimate the fraction
of coherent structures in our dataset. We find that coherent structures
constitute ~2.5 % of the entire dataset, roughly one-tenth of the value
reported in the near-earth environment, indicating in-situ formation
of intermittent magnetic field structures developed by the non-linear
turbulent cascade. We move on to analyze waiting time distributions
of identified events by imposing thresholds on the PVI time series. We
show that the shape of the waiting time distribution strongly depends
on the resolution of the magnetic field time series and the time-lag
used to estimate the PVI time series. We proceed to analyze the
contribution of coherent structures to the heating of the Solar Wind
(SW). We find a positive correlation between proton temperature and
PVI, indicating that proton heating is localized in the vicinity and
strongly correlated with intermittent structures. More precisely,
the strongest discontinuities in the magnetic field are associated
with the most abrupt changes in proton temperature . Still, due to the
scarcity of such events, their relative contribution to the dissipation
of energy in the solar wind is minor. We propose that smaller scale,
more frequent, magnetic field variations of PVI events in the range 2
< PVI< 6, determine the global solar wind temperature. Finally,
our results indicate that due to the low density of coherent structures
in the young solar wind environment, intermittent heating is not as
pronounced as in the outer part of the heliosphere.
---------------------------------------------------------
Title: Are Nanoflares Responsible for Coronal Heating?
Authors: Vlahos, Loukas; Isliker, Heinz; Sioulas, Nikos
2021arXiv210801722V Altcode:
Parker (1983) suggested a mechanism for the formation of current sheets
(CSs) in the solar atmosphere. His main idea was that the tangling of
coronal magnetic field lines by photospheric random flows facilitates
the continuous formation of CSs in the solar atmosphere. This part
of his idea represents one of the many ways by which the turbulent
convection zone drives the formation of coherent structures and CSs
in the solar atmosphere. Other mechanisms include emerging magnetic
flux, interaction of current filaments, and explosive magnetic
structures. However, there are two unproven assumptions in the initial
idea of Parker for the coronal heating through nanoflares that must be
re-examined. They are related to his suggestion that {ALL CSs formed
are led to magnetic reconnection and that magnetic reconnection heats
the plasma in the solar atmosphere. Let us discuss these two assumptions
briefly in this short comment: (1) Are ALL coherent structures and CSs
formed by the turbulent convection zone reconnecting? Does turbulence
associated with non-reconnecting CSs play a role in the heating of
the corona? (2) Does magnetic reconnection heat the plasma?
---------------------------------------------------------
Title: Stochastic Turbulent Acceleration in a Fractal Environment
Authors: Sioulas, Nikos; Isliker, Heinz; Vlahos, Loukas
2020ApJ...895L..14S Altcode: 2020arXiv200502668S
We analyze the stochastic acceleration of particles inside a fully
developed turbulent plasma. It is well known that large-amplitude
magnetic fluctuations and coherent structures in such an environment
obey a fractal scaling, and our specific aim is to study for the first
time the effects of the fractality of these environments on stochastic
acceleration. We have shown that an injected Maxwellian energy
distribution is heated and forms a high-energy tail in a very short
time. Using standard parameters for the low solar corona, the injected
Maxwellian distribution of electrons gets heated from the initial
100 eV to 10 KeV, and the power-law index of the high-energy tail is
about -2.3. The high-energy tail starts around 100 keV, and reaches
10 MeV. The index of the power-law tail depends on the system size,
and it is in good agreement with observed values for realistic system
sizes. The heating and acceleration process is very fast (∼2 s). The
reason why the acceleration time is so short is that the particles
are trapped within small-scale parts of the fractal environment, and
their scattering mean free path reduces drastically. The presence of
small-scale activity also easily pulls particles from the thermal pool,
so there is no need for a seed population. The mean square displacement
in space and energy is superdiffusive for the high-energy particles.
---------------------------------------------------------
Title: Superdiffusive stochastic Fermi acceleration in space and
energy
Authors: Sioulas, N.; Isliker, H.; Vlahos, L.; Koumtzis, A.;
Pisokas, Th
2020MNRAS.491.3860S Altcode: 2019MNRAS.tmp.2837S; 2019arXiv191107973S
We analyse the transport properties of charged particles (ions
and electrons) interacting with randomly formed magnetic scatterers
(e.g. large-scale local 'magnetic fluctuations' or 'coherent magnetic
irregularities' usually present in strongly turbulent plasmas), using
the energization processes proposed initially by Fermi in 1949. The
scatterers are formed by large-scale local fluctuations (δB/B ≈ 1)
and are randomly distributed inside the unstable magnetic topology. We
construct a 3D grid on which a small fraction of randomly chosen grid
points are acting as scatterers. In particular, we study how a large
number of test particles are accelerated and transported inside a
collection of scatterers in a finite volume. Our main results are:
(1) The spatial mean-square displacement <(Δr)<SUP>2</SUP> >
inside the stochastic Fermi accelerator is superdiffusive, < (Δ
r)^2> ∼ t^{a<SUB>r</SUB>}, with a<SUB>r</SUB> ∼ 1.2-1.6, for
the high-energy electrons with kinetic energy (W) larger than 1 MeV,
and it is normal (a<SUB>r</SUB> = 1) for the heated low-energy (W <
10 keV) electrons. (2) The transport properties of the high-energy
particles are closely related with the mean-free path that the
particles travel in-between the scatterers (λ<SUB>sc</SUB>). The
smaller λ<SUB>sc</SUB> is, the faster the electrons and ions escape
from the acceleration volume. (3) The mean displacement in energy
< Δ W> ∼ t^{a<SUB>W</SUB>} is strongly enhanced inside the
acceleration volume (a<SUB>W</SUB> = 1.5-2.5) for the high-energy
particles compared to the thermal low-energy particles (a<SUB>W</SUB>
= 0.4), I.e. high-energy particles undergo an enhanced systematic gain
in energy. (4) The mean-square displacement in energy <W<SUP>2</SUP>
> is superdiffusive for the high-energy particles and normal for
the low-energy, heated particles.
---------------------------------------------------------
Title: Particle Acceleration and Heating in Regions of Magnetic
Flux Emergence
Authors: Isliker, H.; Archontis, V.; Vlahos, L.
2019ApJ...882...57I Altcode: 2019arXiv190704296I
The interaction between emerging and pre-existing magnetic fields
in the solar atmosphere can trigger several dynamic phenomena, such
as eruptions and jets. A key element during this interaction is
the formation of large-scale current sheets, and eventually their
fragmentation that leads to the creation of a strongly turbulent
environment. In this paper, we study the kinetic aspects of the
interaction (reconnection) between emerging and ambient magnetic
fields. We show that the statistical properties of the spontaneously
fragmented and fractal electric fields are responsible for the
efficient heating and acceleration of charged particles, which form a
power-law tail at high energies on sub-second timescales. A fraction
of the energized particles escapes from the acceleration volume, with
a super-hot component with a temperature close to 150 MK, and with a
power-law high-energy tail with an index between -2 and -3. We estimate
the transport coefficients in energy space from the dynamics of the
charged particles inside the fragmented and fractal electric fields, and
the solution of a fractional transport equation, as appropriate for a
strongly turbulent plasma, agrees with the test-particle simulations. We
also show that the acceleration mechanism is not related to Fermi
acceleration, and the Fokker-Planck equation is inconsistent and
not adequate as a transport model. Finally, we address the problem
of correlations between spatial transport and transport in energy
space. Our results confirm the observations reported for high-energy
particles (hard X-rays, type III bursts, and solar energetic particles)
during the emission of solar jets.
---------------------------------------------------------
Title: Introduction to the physics of solar eruptions and their
space weather impact
Authors: Archontis, Vasilis; Vlahos, Loukas
2019RSPTA.37790152A Altcode: 2019arXiv190508361A
The physical processes, which drive powerful solar eruptions, play an
important role in our understanding of the Sun-Earth connection. In this
Special Issue, we firstly discuss how magnetic fields emerge from the
solar interior to the solar surface, to build up active regions, which
commonly host large-scale coronal disturbances, such as coronal mass
ejections (CMEs). Then, we discuss the physical processes associated
with the driving and triggering of these eruptions, the propagation
of the large-scale magnetic disturbances through interplanetary
space and the interaction of CMEs with Earth's magnetic field. The
acceleration mechanisms for the solar energetic particles related to
explosive phenomena (e.g. flares and/or CMEs) in the solar corona
are also discussed. The main aim of this Issue, therefore, is to
encapsulate the present state-of-the-art in research related to the
genesis of solar eruptions and their space-weather implications. <P
/>This article is part of the theme issue `Solar eruptions and their
space weather impact'.
---------------------------------------------------------
Title: Sources of solar energetic particles
Authors: Vlahos, Loukas; Anastasiadis, Anastasios; Papaioannou,
Athanasios; Kouloumvakos, Athanasios; Isliker, Heinz
2019RSPTA.37780095V Altcode: 2019arXiv190308200V
Solar energetic particles are an integral part of the physical processes
related with space weather. We present a review for the acceleration
mechanisms related to the explosive phenomena (flares and/or coronal
mass ejections, CMEs) inside the solar corona. For more than 40 years,
the main two-dimensional cartoon representing our understanding
of the explosive phenomena inside the solar corona remained almost
unchanged. The acceleration mechanisms related to solar flares and
CMEs also remained unchanged and were part of the same cartoon. In this
review, we revise the standard cartoon and present evidence from recent
global magnetohydrodynamic simulations that support the argument that
explosive phenomena will lead to the spontaneous formation of current
sheets in different parts of the erupting magnetic structure. The
evolution of the large-scale current sheets and their fragmentation
will lead to strong turbulence and turbulent reconnection during solar
flares and turbulent shocks. In other words, the acceleration mechanism
in flares and CME-driven shocks may be the same, and their difference
will be the overall magnetic topology, the ambient plasma parameters,
and the duration of the unstable driver. <P />This article is part of
the theme issue `Solar eruptions and their space weather impact'.
---------------------------------------------------------
Title: Particle acceleration and heating in a turbulent solar corona
Authors: Vlahos, Loukas; Isliker, Heinz
2019PPCF...61a4020V Altcode: 2018arXiv180807136V
Turbulence, magnetic reconnection, and shocks can be present
in explosively unstable plasmas, forming a new electromagnetic
environment, which we call here turbulent reconnection, and where
spontaneous formation of current sheets takes place. We will show
that the heating and the acceleration of particles is the result of
the synergy of stochastic (second order Fermi) and systematic (first
order Fermi) acceleration inside fully developed turbulence. The
solar atmosphere is magnetically coupled to a turbulent driver (the
convection zone), therefore the appearance of turbulent reconnection
in the solar atmosphere is externally driven. Turbulent reconnection,
once it is established in the solar corona, drives the coronal heating
and particle acceleration.
---------------------------------------------------------
Title: Statistical Analysis of Individual Solar Active Regions
Authors: Kromyda, Garyfallia; Vlahos, Loukas
2018IAUS..335....3K Altcode:
In the last decades, numerous observational and computational studies
have shown that the global flare distribution is a power-law with
a slope less than 2. In these studies, active regions are treated
as statistically indistinguishable. To test this, we identify and
separately analyze the flares produced by ten individual active
regions (2006-2016). In five regions, we find a single power-law
distribution, with a slope of a < 2. In the other five, we find a
broken double power-law distribution, with slopes a<SUB>1</SUB> <
2 and a<SUB>2</SUB> > 2.
---------------------------------------------------------
Title: Diffusive shock acceleration and turbulent reconnection
Authors: Garrel, Christian; Vlahos, Loukas; Isliker, Heinz; Pisokas,
Theophilos
2018MNRAS.478.2976G Altcode: 2018arXiv180505143G; 2018MNRAS.tmp.1205G
Diffusive shock acceleration (DSA) cannot efficiently accelerate
particles without the presence of self-consistently generated or
pre-existing strong turbulence (δB/B∼ 1) in the vicinity of the
shock. The problem we address in this article is: if large-amplitude
magnetic disturbances are present upstream and downstream of a shock
then Turbulent Reconnection (TR) will set in and will participate
not only in the elastic scattering of particles but also in their
heating and acceleration. We demonstrate that large-amplitude magnetic
disturbances and Unstable Current Sheets (UCS), spontaneously formed
in the strong turbulence in the vicinity of a shock, can accelerate
particles as efficiently as DSA in large-scale systems and on long
time scales. We start our analysis with `elastic' scatterers upstream
and downstream and estimate the energy distribution of particles
escaping from the shock, recovering the well-known results from the DSA
theory. Next we analyse the additional interaction of the particles
with active scatterers (magnetic disturbances and UCS) upstream and
downstream of the shock. We show that the asymptotic energy distribution
of the particles accelerated by DSA/TR has very similar characteristics
with the one due to DSA alone, but the synergy of DSA with TR is much
more efficient: The acceleration time is an order of magnitude shorter
and the maximum energy reached two orders of magnitude higher. We claim
that DSA is the dominant acceleration mechanism in a short period before
TR is established, and then strong turbulence will dominate the heating
and acceleration of the particles. In other words, the shock serves
as the mechanism to set up a strongly turbulent environment, in which
the acceleration mechanism will ultimately be the synergy of DSA and TR.
---------------------------------------------------------
Title: Synergy of Stochastic and Systematic Energization of Plasmas
during Turbulent Reconnection
Authors: Pisokas, Theophilos; Vlahos, Loukas; Isliker, Heinz
2018ApJ...852...64P Altcode: 2017arXiv171203517P
The important characteristic of turbulent reconnection is that it
combines large-scale magnetic disturbances (δ B/B∼ 1) with randomly
distributed unstable current sheets (UCSs). Many well-known nonlinear
MHD structures (strong turbulence, current sheet(s), shock(s)) lead
asymptotically to the state of turbulent reconnection. We analyze
in this article, for the first time, the energization of electrons
and ions in a large-scale environment that combines large-amplitude
disturbances propagating with sub-Alfvénic speed with UCSs. The
magnetic disturbances interact stochastically (second-order Fermi) with
the charged particles and play a crucial role in the heating of the
particles, while the UCSs interact systematically (first-order Fermi)
and play a crucial role in the formation of the high-energy tail. The
synergy of stochastic and systematic acceleration provided by the
mixture of magnetic disturbances and UCSs influences the energetics
of the thermal and nonthermal particles, the power-law index, and
the length of time the particles remain inside the energy release
volume. We show that this synergy can explain the observed very fast
and impulsive particle acceleration and the slightly delayed formation
of a superhot particle population.
---------------------------------------------------------
Title: Particle Acceleration and Fractional Transport in Turbulent
Reconnection
Authors: Isliker, Heinz; Pisokas, Theophilos; Vlahos, Loukas;
Anastasiadis, Anastasios
2017ApJ...849...35I Altcode: 2017arXiv170908269I
We consider a large-scale environment of turbulent reconnection
that is fragmented into a number of randomly distributed unstable
current sheets (UCSs), and we statistically analyze the acceleration
of particles within this environment. We address two important cases
of acceleration mechanisms when particles interact with the UCS:
(a) electric field acceleration and (b) acceleration by reflection
at contracting islands. Electrons and ions are accelerated very
efficiently, attaining an energy distribution of power-law shape with
an index 1-2, depending on the acceleration mechanism. The transport
coefficients in energy space are estimated from test-particle simulation
data, and we show that the classical Fokker-Planck (FP) equation fails
to reproduce the simulation results when the transport coefficients
are inserted into it and it is solved numerically. The cause for this
failure is that the particles perform Levy flights in energy space,
while the distributions of the energy increments exhibit power-law
tails. We then use the fractional transport equation (FTE) derived
by Isliker et al., whose parameters and the order of the fractional
derivatives are inferred from the simulation data, and solving the FTE
numerically, we show that the FTE successfully reproduces the kinetic
energy distribution of the test particles. We discuss in detail the
analysis of the simulation data and the criteria that allow one to
judge the appropriateness of either an FTE or a classical FP equation
as a transport model.
---------------------------------------------------------
Title: Stochastic Fermi Energization of Coronal Plasma during
Explosive Magnetic Energy Release
Authors: Pisokas, Theophilos; Vlahos, Loukas; Isliker, Heinz; Tsiolis,
Vassilis; Anastasiadis, Anastasios
2017ApJ...835..214P Altcode: 2016arXiv161204246P
The aim of this study is to analyze the interaction of charged particles
(ions and electrons) with randomly formed particle scatterers (e.g.,
large-scale local “magnetic fluctuations” or “coherent magnetic
irregularities”) using the setup proposed initially by Fermi. These
scatterers are formed by the explosive magnetic energy release
and propagate with the Alfvén speed along the irregular magnetic
fields. They are large-scale local fluctuations (δB/B ≈ 1) randomly
distributed inside the unstable magnetic topology and will here be
called Alfvénic Scatterers (AS). We constructed a 3D grid on which
a small fraction of randomly chosen grid points are acting as AS. In
particular, we study how a large number of test particles evolves inside
a collection of AS, analyzing the evolution of their energy distribution
and their escape-time distribution. We use a well-established method to
estimate the transport coefficients directly from the trajectories of
the particles. Using the estimated transport coefficients and solving
the Fokker-Planck equation numerically, we can recover the energy
distribution of the particles. We have shown that the stochastic Fermi
energization of mildly relativistic and relativistic plasma can heat and
accelerate the tail of the ambient particle distribution as predicted
by Parker & Tidman and Ramaty. The temperature of the hot plasma
and the tail of the energetic particles depend on the mean free path
(λ<SUB>sc</SUB>) of the particles between the scatterers inside the
energization volume.
---------------------------------------------------------
Title: Limits of applicability of the quasilinear approximation to
the electrostatic wave-plasma interaction
Authors: Zacharegkas, Georgios; Isliker, Heinz; Vlahos, Loukas
2016PhPl...23k2119Z Altcode: 2016arXiv161103792Z
The limitation of the Quasilinear Theory (QLT) to describe the diffusion
of electrons and ions in velocity space when interacting with a spectrum
of large amplitude electrostatic Langmuir, Upper and Lower hybrid waves,
is analyzed. We analytically and numerically estimate the threshold
for the amplitude of the waves above which the QLT breaks down, using
a test particle code. The evolution of the velocity distribution,
the velocity-space diffusion coefficients, the driven current, and
the heating of the particles are investigated, for the interaction
with small and large amplitude electrostatic waves, that is, in both
regimes, where QLT is valid and where it clearly breaks down.
---------------------------------------------------------
Title: An observationally-driven kinetic approach to coronal heating
Authors: Moraitis, K.; Toutountzi, A.; Isliker, H.; Georgoulis, M.;
Vlahos, L.; Chintzoglou, G.
2016A&A...596A..56M Altcode: 2016arXiv160307129M; 2016arXiv160307129T
<BR /> Aims: Coronal heating through the explosive release of magnetic
energy remains an open problem in solar physics. Recent hydrodynamical
models attempt an investigation by placing swarms of "nanoflares" at
random sites and times in modeled one-dimensional coronal loops. We
investigate the problem in three dimensions, using extrapolated coronal
magnetic fields of observed solar active regions. <BR /> Methods: We
applied a nonlinear force-free field extrapolation above an observed
photospheric magnetogram of NOAA active region (AR) 11 158. We then
determined the locations, energy contents, and volumes of "unstable"
areas, namely areas prone to releasing magnetic energy due to locally
accumulated electric current density. Statistical distributions of
these volumes and their fractal dimension are inferred, investigating
also their dependence on spatial resolution. Further adopting a
simple resistivity model, we inferred the properties of the fractally
distributed electric fields in these volumes. Next, we monitored the
evolution of 10<SUP>5</SUP> particles (electrons and ions) obeying
an initial Maxwellian distribution with a temperature of 10 eV,
by following their trajectories and energization when subjected
to the resulting electric fields. For computational convenience,
the length element of the magnetic-field extrapolation is 1 arcsec,
or 725 km, much coarser than the particles' collisional mean free
path in the low corona (0.1-1 km). <BR /> Results: The presence of
collisions traps the bulk of the plasma around the unstable volumes,
or current sheets (UCS), with only a tail of the distribution gaining
substantial energy. Assuming that the distance between UCS is similar
to the collisional mean free path we find that the low active-region
corona is heated to 100-200 eV, corresponding to temperatures exceeding
2 MK, within tens of seconds for electrons and thousands of seconds for
ions. <BR /> Conclusions: Fractally distributed, nanoflare-triggening
fragmented UCS in the active-region corona can heat electrons and ions
with minor enhancements of the local resistivity. This statistical
result is independent from the nature of the extrapolation and the
spatial resolution of the modeled active-region corona. This finding
should be coupled with a complete plasma treatment to determine whether
a quasi-steady temperature similar to that of the ambient corona can be
maintained, either via a kinetic or via a hybrid, kinetic and fluid,
plasma treatment. The finding can also be extended to the quiet solar
corona, provided that the currently undetected nanoflares are frequent
enough to account for the lower (compared to active regions) energy
losses in this case.
---------------------------------------------------------
Title: Contributions of the Cherenkov Telescope Array (CTA) to
the 6th International Symposium on High-Energy Gamma-Ray Astronomy
(Gamma 2016)
Authors: CTA Consortium, The; :; Abchiche, A.; Abeysekara, U.; Abril,
Ó.; Acero, F.; Acharya, B. S.; Adams, C.; Agnetta, G.; Aharonian,
F.; Akhperjanian, A.; Albert, A.; Alcubierre, M.; Alfaro, J.; Alfaro,
R.; Allafort, A. J.; Aloisio, R.; Amans, J. -P.; Amato, E.; Ambrogi,
L.; Ambrosi, G.; Ambrosio, M.; Anderson, J.; Anduze, M.; Angüner,
E. O.; Antolini, E.; Antonelli, L. A.; Antonucci, M.; Antonuccio,
V.; Antoranz, P.; Aramo, C.; Aravantinos, A.; Araya, M.; Arcaro, C.;
Arezki, B.; Argan, A.; Armstrong, T.; Arqueros, F.; Arrabito, L.;
Arrieta, M.; Asano, K.; Ashley, M.; Aubert, P.; Singh, C. B.; Babic,
A.; Backes, M.; Bais, A.; Bajtlik, S.; Balazs, C.; Balbo, M.; Balis,
D.; Balkowski, C.; Ballester, O.; Ballet, J.; Balzer, A.; Bamba,
A.; Bandiera, R.; Barber, A.; Barbier, C.; Barcelo, M.; Barkov,
M.; Barnacka, A.; Barres de Almeida, U.; Barrio, J. A.; Basso, S.;
Bastieri, D.; Bauer, C.; Becciani, U.; Becherini, Y.; Becker Tjus,
J.; Beckmann, V.; Bednarek, W.; Benbow, W.; Benedico Ventura, D.;
Berdugo, J.; Berge, D.; Bernardini, E.; Bernardini, M. G.; Bernhard,
S.; Bernlöhr, K.; Bertucci, B.; Besel, M. -A.; Beshley, V.; Bhatt,
N.; Bhattacharjee, P.; Bhattacharyya, W.; Bhattachryya, S.; Biasuzzi,
B.; Bicknell, G.; Bigongiari, C.; Biland, A.; Bilinsky, A.; Bilnik,
W.; Biondo, B.; Bird, R.; Bird, T.; Bissaldi, E.; Bitossi, M.;
Blanch, O.; Blasi, P.; Blazek, J.; Bockermann, C.; Boehm, C.; Bogacz,
L.; Bogdan, M.; Bohacova, M.; Boisson, C.; Boix, J.; Bolmont, J.;
Bonanno, G.; Bonardi, A.; Bonavolontà, C.; Bonifacio, P.; Bonnarel,
F.; Bonnoli, G.; Borkowski, J.; Bose, R.; Bosnjak, Z.; Böttcher, M.;
Bousquet, J. -J.; Boutonnet, C.; Bouyjou, F.; Bowman, L.; Braiding,
C.; Brantseg, T.; Brau-Nogué, S.; Bregeon, J.; Briggs, M.; Brigida,
M.; Bringmann, T.; Brisken, W.; Bristow, D.; Britto, R.; Brocato, E.;
Bron, S.; Brook, P.; Brooks, W.; Brown, A. M.; Brügge, K.; Brun, F.;
Brun, P.; Brun, P.; Brunetti, G.; Brunetti, L.; Bruno, P.; Buanes,
T.; Bucciantini, N.; Buchholtz, G.; Buckley, J.; Bugaev, V.; Bühler,
R.; Bulgarelli, A.; Bulik, T.; Burton, M.; Burtovoi, A.; Busetto,
G.; Buson, S.; Buss, J.; Byrum, K.; Cadoux, F.; Calvo Tovar, J.;
Cameron, R.; Canelli, F.; Canestrari, R.; Capalbi, M.; Capasso, M.;
Capobianco, G.; Caproni, A.; Caraveo, P.; Cardenzana, J.; Cardillo,
M.; Carius, S.; Carlile, C.; Carosi, A.; Carosi, R.; Carquín, E.;
Carr, J.; Carroll, M.; Carter, J.; Carton, P. -H.; Casandjian, J. -M.;
Casanova, S.; Casanova, S.; Cascone, E.; Casiraghi, M.; Castellina,
A.; Castroviejo Mora, J.; Catalani, F.; Catalano, O.; Catalanotti,
S.; Cauz, D.; Cavazzani, S.; Cerchiara, P.; Chabanne, E.; Chadwick,
P.; Chaleil, T.; Champion, C.; Chatterjee, A.; Chaty, S.; Chaves, R.;
Chen, A.; Chen, X.; Chen, X.; Cheng, K.; Chernyakova, M.; Chiappetti,
L.; Chikawa, M.; Chinn, D.; Chitnis, V. R.; Cho, N.; Christov, A.;
Chudoba, J.; Cieślar, M.; Ciocci, M. A.; Clay, R.; Colafrancesco,
S.; Colin, P.; Colley, J. -M.; Colombo, E.; Colome, J.; Colonges, S.;
Conforti, V.; Connaughton, V.; Connell, S.; Conrad, J.; Contreras,
J. L.; Coppi, P.; Corbel, S.; Coridian, J.; Cornat, R.; Corona,
P.; Corti, D.; Cortina, J.; Cossio, L.; Costa, A.; Costantini, H.;
Cotter, G.; Courty, B.; Covino, S.; Covone, G.; Crimi, G.; Criswell,
S. J.; Crocker, R.; Croston, J.; Cuadra, J.; Cumani, P.; Cusumano,
G.; Da Vela, P.; Dale, Ø.; D'Ammando, F.; Dang, D.; Dang, V. T.;
Dangeon, L.; Daniel, M.; Davids, I.; Davids, I.; Dawson, B.; Dazzi,
F.; de Aguiar Costa, B.; De Angelis, A.; de Araujo Cardoso, R. F.;
De Caprio, V.; de Cássia dos Anjos, R.; De Cesare, G.; De Franco,
A.; De Frondat, F.; de Gouveia Dal Pino, E. M.; de la Calle, I.;
De Lisio, C.; de los Reyes Lopez, R.; De Lotto, B.; De Luca, A.; de
Mello Neto, J. R. T.; de Naurois, M.; de Oña Wilhelmi, E.; De Palma,
F.; De Persio, F.; de Souza, V.; Decock, G.; Decock, J.; Deil, C.;
Del Santo, M.; Delagnes, E.; Deleglise, G.; Delgado, C.; Delgado, J.;
della Volpe, D.; Deloye, P.; Detournay, M.; Dettlaff, A.; Devin, J.;
Di Girolamo, T.; Di Giulio, C.; Di Paola, A.; Di Pierro, F.; Diaz,
M. A.; Díaz, C.; Dib, C.; Dick, J.; Dickinson, H.; Diebold, S.;
Digel, S.; Dipold, J.; Disset, G.; Distefano, A.; Djannati-Ataï, A.;
Doert, M.; Dohmke, M.; Domínguez, A.; Dominik, N.; Dominique, J. -L.;
Dominis Prester, D.; Donat, A.; Donnarumma, I.; Dorner, D.; Doro,
M.; Dournaux, J. -L.; Downes, T.; Doyle, K.; Drake, G.; Drappeau,
S.; Drass, H.; Dravins, D.; Drury, L.; Dubus, G.; Ducci, L.; Dumas,
D.; Dundas Morå, K.; Durand, D.; D'Urso, D.; Dwarkadas, V.; Dyks,
J.; Dyrda, M.; Ebr, J.; Edy, E.; Egberts, K.; Eger, P.; Egorov, A.;
Einecke, S.; Eisch, J.; Eisenkolb, F.; Eleftheriadis, C.; Elsaesser,
D.; Elsässer, D.; Emmanoulopoulos, D.; Engelbrecht, C.; Engelhaupt,
D.; Ernenwein, J. -P.; Escarate, P.; Eschbach, S.; Espinoza, C.;
Evans, P.; Fairbairn, M.; Falceta-Goncalves, D.; Falcone, A.; Fallah
Ramazani, V.; Fantinel, D.; Farakos, K.; Farnier, C.; Farrell, E.;
Fasola, G.; Favre, Y.; Fede, E.; Fedora, R.; Fedorova, E.; Fegan, S.;
Ferenc, D.; Fernandez-Alonso, M.; Fernández-Barral, A.; Ferrand, G.;
Ferreira, O.; Fesquet, M.; Fetfatzis, P.; Fiandrini, E.; Fiasson, A.;
Filipčič, A.; Filipovic, M.; Fink, D.; Finley, C.; Finley, J. P.;
Finoguenov, A.; Fioretti, V.; Fiorini, M.; Fleischhack, H.; Flores,
H.; Florin, D.; Föhr, C.; Fokitis, E.; Fonseca, M. V.; Font, L.;
Fontaine, G.; Fontes, B.; Fornasa, M.; Fornasa, M.; Förster, A.;
Fortin, P.; Fortson, L.; Fouque, N.; Franckowiak, A.; Franckowiak,
A.; Franco, F. J.; Freire Mota Albuquerque, I.; Freixas Coromina,
L.; Fresnillo, L.; Fruck, C.; Fuessling, M.; Fugazza, D.; Fujita, Y.;
Fukami, S.; Fukazawa, Y.; Fukuda, T.; Fukui, Y.; Funk, S.; Furniss, A.;
Gäbele, W.; Gabici, S.; Gadola, A.; Galindo, D.; Gall, D. D.; Gallant,
Y.; Galloway, D.; Gallozzi, S.; Galvez, J. A.; Gao, S.; Garcia, A.;
Garcia, B.; García Gil, R.; Garcia López, R.; Garczarczyk, M.;
Gardiol, D.; Gargano, C.; Gargano, F.; Garozzo, S.; Garrecht, F.;
Garrido, L.; Garrido-Ruiz, M.; Gascon, D.; Gaskins, J.; Gaudemard,
J.; Gaug, M.; Gaweda, J.; Gebhardt, B.; Gebyehu, M.; Geffroy, N.;
Genolini, B.; Gerard, L.; Ghalumyan, A.; Ghedina, A.; Ghislain, P.;
Giammaria, P.; Giannakaki, E.; Gianotti, F.; Giarrusso, S.; Giavitto,
G.; Giebels, B.; Gieras, T.; Giglietto, N.; Gika, V.; Gimenes, R.;
Giomi, M.; Giommi, P.; Giordano, F.; Giovannini, G.; Girardot, P.;
Giro, E.; Giroletti, M.; Gironnet, J.; Giuliani, A.; Glicenstein,
J. -F.; Gnatyk, R.; Godinovic, N.; Goldoni, P.; Gomez, G.; Gonzalez,
M. M.; González, A.; Gora, D.; Gothe, K. S.; Gotz, D.; Goullon, J.;
Grabarczyk, T.; Graciani, R.; Graham, J.; Grandi, P.; Granot, J.;
Grasseau, G.; Gredig, R.; Green, A. J.; Green, A. M.; Greenshaw, T.;
Grenier, I.; Griffiths, S.; Grillo, A.; Grondin, M. -H.; Grube, J.;
Grudzinska, M.; Grygorczuk, J.; Guarino, V.; Guberman, D.; Gunji, S.;
Gyuk, G.; Hadasch, D.; Hagedorn, A.; Hagge, L.; Hahn, J.; Hakobyan,
H.; Hara, S.; Hardcastle, M. J.; Hassan, T.; Hatanaka, K.; Haubold,
T.; Haupt, A.; Hayakawa, T.; Hayashida, M.; Heller, M.; Heller,
R.; Helo, J. C.; Henault, F.; Henri, G.; Hermann, G.; Hermel, R.;
Herrera Llorente, J.; Herrera Llorente, J.; Herrero, A.; Hervet,
O.; Hidaka, N.; Hinton, J.; Hirai, W.; Hirotani, K.; Hnatyk, B.;
Hoang, J.; Hoffmann, D.; Hofmann, W.; Holch, T.; Holder, J.; Hooper,
S.; Horan, D.; Hörandel, J.; Hörbe, M.; Horns, D.; Horvath, P.;
Hose, J.; Houles, J.; Hovatta, T.; Hrabovsky, M.; Hrupec, D.; Huet,
J. -M.; Huetten, M.; Hughes, G.; Hui, D.; Humensky, T. B.; Hussein,
M.; Iacovacci, M.; Ibarra, A.; Ikeno, Y.; Illa, J. M.; Impiombato,
D.; Inada, T.; Incorvaia, S.; Infante, L.; Inome, Y.; Inoue, S.;
Inoue, T.; Inoue, Y.; Iocco, F.; Ioka, K.; Iori, M.; Ishio, K.;
Ishio, K.; Israel, G. L.; Iwamura, Y.; Jablonski, C.; Jacholkowska,
A.; Jacquemier, J.; Jamrozy, M.; Janecek, P.; Janiak, M.; Jankowsky,
D.; Jankowsky, F.; Jean, P.; Jegouzo, I.; Jenke, P.; Jimenez, J. J.;
Jingo, M.; Jingo, M.; Jocou, L.; Jogler, T.; Johnson, C. A.; Jones,
M.; Josselin, M.; Journet, L.; Jung, I.; Kaaret, P.; Kagaya, M.;
Kakuwa, J.; Kalekin, O.; Kalkuhl, C.; Kamon, H.; Kankanyan, R.;
Karastergiou, A.; Kärcher, K.; Karczewski, M.; Karkar, S.; Karn, P.;
Kasperek, J.; Katagiri, H.; Kataoka, J.; Katarzyński, K.; Kato, S.;
Katz, U.; Kawanaka, N.; Kaye, L.; Kazanas, D.; Kelley-Hoskins, N.;
Kersten, J.; Khélifi, B.; Kieda, D. B.; Kihm, T.; Kimeswenger, S.;
Kisaka, S.; Kishida, S.; Kissmann, R.; Klepser, S.; Kluźniak, W.;
Knapen, J.; Knapp, J.; Knödlseder, J.; Koch, B.; Köck, F.; Kocot,
J.; Kohri, K.; Kokkotas, K.; Kokkotas, K.; Kolitzus, D.; Komin, N.;
Kominis, I.; Kong, A.; Konno, Y.; Kosack, K.; Koss, G.; Kossatz, M.;
Kowal, G.; Koyama, S.; Kozioł, J.; Kraus, M.; Krause, J.; Krause, M.;
Krawzcynski, H.; Krennrich, F.; Kretzschmann, A.; Kruger, P.; Kubo, H.;
Kudryavtsev, V.; Kukec Mezek, G.; Kuklis, M.; Kuroda, H.; Kushida, J.;
La Barbera, A.; La Palombara, N.; La Parola, V.; La Rosa, G.; Laffon,
H.; Lahmann, R.; Lakicevic, M.; Lalik, K.; Lamanna, G.; Landriu,
D.; Landt, H.; Lang, R. G.; Lapington, J.; Laporte, P.; Le Fèvre,
J. -P.; Le Flour, T.; Le Sidaner, P.; Lee, S. -H.; Lee, W. H.; Lees,
J. -P.; Lefaucheur, J.; Leffhalm, K.; Leich, H.; Leigui de Oliveira,
M. A.; Lelas, D.; Lemière, A.; Lemoine-Goumard, M.; Lenain, J. -P.;
Leonard, R.; Leoni, R.; Lessio, L.; Leto, G.; Leveque, A.; Lieunard,
B.; Limon, M.; Lindemann, R.; Lindfors, E.; Linhoff, L.; Liolios,
A.; Lipniacka, A.; Lockart, H.; Lohse, T.; Łokas, E.; Lombardi, S.;
Longo, F.; Lopatin, A.; Lopez, M.; Loreggia, D.; Louge, T.; Louis,
F.; Louys, M.; Lucarelli, F.; Lucchesi, D.; Lüdecke, H.; Luigi, T.;
Luque-Escamilla, P. L.; Lyard, E.; Maccarone, M. C.; Maccarone, T.;
Maccarone, T. J.; Mach, E.; Madejski, G. M.; Madonna, A.; Magniette,
F.; Magniez, A.; Mahabir, M.; Maier, G.; Majumdar, P.; Majumdar, P.;
Makariev, M.; Malaguti, G.; Malaspina, G.; Mallot, A. K.; Malouf,
A.; Maltezos, S.; Malyshev, D.; Mancilla, A.; Mandat, D.; Maneva, G.;
Manganaro, M.; Mangano, S.; Manigot, P.; Mankushiyil, N.; Mannheim, K.;
Maragos, N.; Marano, D.; Marchegiani, P.; Marcomini, J. A.; Marcowith,
A.; Mariotti, M.; Marisaldi, M.; Markoff, S.; Martens, C.; Martí,
J.; Martin, J. -M.; Martin, L.; Martin, P.; Martínez, G.; Martínez,
M.; Martínez, O.; Martynyuk-Lototskyy, K.; Marx, R.; Masetti, N.;
Massimino, P.; Mastichiadis, A.; Mastroianni, S.; Mastropietro, M.;
Masuda, S.; Matsumoto, H.; Matsuoka, S.; Matthews, N.; Mattiazzo, S.;
Maurin, G.; Maxted, N.; Maxted, N.; Maya, J.; Mayer, M.; Mazin, D.;
Mazziotta, M. N.; Mc Comb, L.; McCubbin, N.; McHardy, I.; Medina,
C.; Mehrez, F.; Melioli, C.; Melkumyan, D.; Melse, T.; Mereghetti,
S.; Merk, M.; Mertsch, P.; Meunier, J. -L.; Meures, T.; Meyer, M.;
Meyrelles, J. L., jr; Miccichè, A.; Michael, T.; Michałowski, J.;
Mientjes, P.; Mievre, I.; Mihailidis, A.; Miller, J.; Mineo, T.;
Minuti, M.; Mirabal, N.; Mirabel, F.; Miranda, J. M.; Mirzoyan, R.;
Mitchell, A.; Mizuno, T.; Moderski, R.; Mognet, I.; Mohammed, M.;
Moharana, R.; Mohrmann, L.; Molinari, E.; Molyneux, P.; Monmarthe,
E.; Monnier, G.; Montaruli, T.; Monte, C.; Monteiro, I.; Mooney, D.;
Moore, P.; Moralejo, A.; Morello, C.; Moretti, E.; Mori, K.; Morris,
P.; Morselli, A.; Moscato, F.; Motohashi, D.; Mottez, F.; Moudden,
Y.; Moulin, E.; Mueller, S.; Mukherjee, R.; Munar, P.; Munari, M.;
Mundell, C.; Mundet, J.; Muraishi, H.; Murase, K.; Muronga, A.; Murphy,
A.; Nagar, N.; Nagataki, S.; Nagayoshi, T.; Nagesh, B. K.; Naito,
T.; Nakajima, D.; Nakajima, D.; Nakamori, T.; Nakayama, K.; Nanni,
J.; Naumann, D.; Nayman, P.; Nellen, L.; Nemmen, R.; Neronov, A.;
Neyroud, N.; Nguyen, T.; Nguyen, T. T.; Nguyen Trung, T.; Nicastro, L.;
Nicolau-Kukliński, J.; Niederwanger, F.; Niedźwiecki, A.; Niemiec,
J.; Nieto, D.; Nievas-Rosillo, M.; Nikolaidis, A.; Nikołajuk, M.;
Nishijima, K.; Nishikawa, K. -I.; Nishiyama, G.; Noda, K.; Noda,
K.; Nogues, L.; Nolan, S.; Northrop, R.; Nosek, D.; Nöthe, M.;
Novosyadlyj, B.; Nozka, L.; Nunio, F.; Oakes, L.; O'Brien, P.; Ocampo,
C.; Occhipinti, G.; Ochoa, J. P.; OFaolain de Bhroithe, A.; Oger, R.;
Ohira, Y.; Ohishi, M.; Ohm, S.; Ohoka, H.; Okazaki, N.; Okumura, A.;
Olive, J. -F.; Olszowski, D.; Ong, R. A.; Ono, S.; Orienti, M.; Orito,
R.; Orlati, A.; Osborne, J.; Ostrowski, M.; Ottaway, D.; Otte, N.;
Öttl, S.; Ovcharov, E.; Oya, I.; Ozieblo, A.; Padovani, M.; Pagano,
I.; Paiano, S.; Paizis, A.; Palacio, J.; Palatka, M.; Pallotta, J.;
Panagiotidis, K.; Panazol, J. -L.; Paneque, D.; Panter, M.; Panzera,
M. R.; Paoletti, R.; Paolillo, M.; Papayannis, A.; Papyan, G.; Paravac,
A.; Paredes, J. M.; Pareschi, G.; Park, N.; Parsons, D.; Paśko, P.;
Pavy, S.; Pech, M.; Peck, A.; Pedaletti, G.; Pe'er, A.; Peet, S.;
Pelat, D.; Pepato, A.; Perez, M. d. C.; Perri, L.; Perri, M.; Persic,
M.; Persic, M.; Petrashyk, A.; Petrucci, P. -O.; Petruk, O.; Peyaud,
B.; Pfeifer, M.; Pfeiffer, G.; Piano, G.; Pieloth, D.; Pierre, E.;
Pinto de Pinho, F.; García, C. Pio; Piret, Y.; Pisarski, A.; Pita,
S.; Platos, Ł.; Platzer, R.; Podkladkin, S.; Pogosyan, L.; Pohl,
M.; Poinsignon, P.; Pollo, A.; Porcelli, A.; Porthault, J.; Potter,
W.; Poulios, S.; Poutanen, J.; Prandini, E.; Prandini, E.; Prast, J.;
Pressard, K.; Principe, G.; Profeti, F.; Prokhorov, D.; Prokoph, H.;
Prouza, M.; Pruchniewicz, R.; Pruteanu, G.; Pueschel, E.; Pühlhofer,
G.; Puljak, I.; Punch, M.; Pürckhauer, S.; Pyzioł, R.; Queiroz,
F.; Quel, E. J.; Quinn, J.; Quirrenbach, A.; Rafighi, I.; Rainò, S.;
Rajda, P. J.; Rameez, M.; Rando, R.; Rannot, R. C.; Rataj, M.; Ravel,
T.; Razzaque, S.; Reardon, P.; Reichardt, I.; Reimann, O.; Reimer,
A.; Reimer, O.; Reisenegger, A.; Renaud, M.; Renner, S.; Reposeur,
T.; Reville, B.; Rezaeian, A.; Rhode, W.; Ribeiro, D.; Ribeiro Prado,
R.; Ribó, M.; Richards, G.; Richer, M. G.; Richtler, T.; Rico, J.;
Ridky, J.; Rieger, F.; Riquelme, M.; Ristori, P. R.; Rivoire, S.; Rizi,
V.; Roache, E.; Rodriguez, J.; Rodriguez Fernandez, G.; Rodríguez
Vázquez, J. J.; Rojas, G.; Romano, P.; Romeo, G.; Roncadelli, M.;
Rosado, J.; Rose, J.; Rosen, S.; Rosier Lees, S.; Ross, D.; Rouaix,
G.; Rousselle, J.; Rovero, A. C.; Rowell, G.; Roy, F.; Royer, S.;
Rubini, A.; Rudak, B.; Rugliancich, A.; Rujopakarn, W.; Rulten,
C.; Rupiński, M.; Russo, F.; Russo, F.; Rutkowski, K.; Saavedra,
O.; Sabatini, S.; Sacco, B.; Sadeh, I.; Saemann, E. O.; Safi-Harb,
S.; Saggion, A.; Sahakian, V.; Saito, T.; Sakaki, N.; Sakurai, S.;
Salamon, A.; Salega, M.; Salek, D.; Salesa Greus, F.; Salgado, J.;
Salina, G.; Salinas, L.; Salini, A.; Sanchez, D.; Sanchez-Conde, M.;
Sandaker, H.; Sandoval, A.; Sangiorgi, P.; Sanguillon, M.; Sano, H.;
Santander, M.; Santangelo, A.; Santos, E. M.; Santos-Lima, R.; Sanuy,
A.; Sapozhnikov, L.; Sarkar, S.; Satalecka, K.; Satalecka, K.; Sato,
Y.; Savalle, R.; Sawada, M.; Sayède, F.; Schanne, S.; Schanz, T.;
Schioppa, E. J.; Schlenstedt, S.; Schmid, J.; Schmidt, T.; Schmoll,
J.; Schneider, M.; Schoorlemmer, H.; Schovanek, P.; Schubert, A.;
Schullian, E. -M.; Schultze, J.; Schulz, A.; Schulz, S.; Schure, K.;
Schussler, F.; Schwab, T.; Schwanke, U.; Schwarz, J.; Schweizer, T.;
Schwemmer, S.; Schwendicke, U.; Schwerdt, C.; Sciacca, E.; Scuderi,
S.; Segreto, A.; Seiradakis, J. -H.; Sembroski, G. H.; Semikoz, D.;
Sergijenko, O.; Serre, N.; Servillat, M.; Seweryn, K.; Shafi, N.;
Shalchi, A.; Sharma, M.; Shayduk, M.; Shellard, R. C.; Shibata, T.;
Shigenaka, A.; Shilon, I.; Shum, E.; Sidoli, L.; Sidz, M.; Sieiro, J.;
Siejkowski, H.; Silk, J.; Sillanpää, A.; Simone, D.; Simpson, H.;
Singh, B. B.; Sinha, A.; Sironi, G.; Sitarek, J.; Sizun, P.; Sliusar,
V.; Sliusar, V.; Smith, A.; Sobczyńska, D.; Sol, H.; Sottile, G.;
Sowiński, M.; Spanier, F.; Spengler, G.; Spiga, R.; Stadler, R.;
Stahl, O.; Stamerra, A.; Stanič, S.; Starling, R.; Staszak, D.;
Stawarz, Ł.; Steenkamp, R.; Stefanik, S.; Stegmann, C.; Steiner, S.;
Stella, C.; Stephan, M.; Stergioulas, N.; Sternberger, R.; Sterzel, M.;
Stevenson, B.; Stinzing, F.; Stodulska, M.; Stodulski, M.; Stolarczyk,
T.; Stratta, G.; Straumann, U.; Stringhetti, L.; Strzys, M.; Stuik,
R.; Sulanke, K. -H.; Suomijärvi, T.; Supanitsky, A. D.; Suric, T.;
Sushch, I.; Sutcliffe, P.; Sykes, J.; Szanecki, M.; Szepieniec, T.;
Szwarnog, P.; Tacchini, A.; Tachihara, K.; Tagliaferri, G.; Tajima,
H.; Takahashi, H.; Takahashi, K.; Takahashi, M.; Takalo, L.; Takami,
S.; Takata, J.; Takeda, J.; Talbot, G.; Tam, T.; Tanaka, M.; Tanaka,
S.; Tanaka, T.; Tanaka, Y.; Tanci, C.; Tanigawa, S.; Tavani, M.;
Tavecchio, F.; Tavernet, J. -P.; Tayabaly, K.; Taylor, A.; Tejedor,
L. A.; Telezhinsky, I.; Temme, F.; Temnikov, P.; Tenzer, C.; Terada,
Y.; Terrazas, J. C.; Terrier, R.; Terront, D.; Terzic, T.; Tescaro,
D.; Teshima, M.; Teshima, M.; Testa, V.; Tezier, D.; Thayer, J.;
Thornhill, J.; Thoudam, S.; Thuermann, D.; Tibaldo, L.; Tiengo,
A.; Timpanaro, M. C.; Tiziani, D.; Tluczykont, M.; Todero Peixoto,
C. J.; Tokanai, F.; Tokarz, M.; Toma, K.; Tomastik, J.; Tomono, Y.;
Tonachini, A.; Tonev, D.; Torii, K.; Tornikoski, M.; Torres, D. F.;
Torres, M.; Torresi, E.; Toso, G.; Tosti, G.; Totani, T.; Tothill, N.;
Toussenel, F.; Tovmassian, G.; Toyama, T.; Travnicek, P.; Trichard,
C.; Trifoglio, M.; Troyano Pujadas, I.; Trzeciak, M.; Tsinganos, K.;
Tsujimoto, S.; Tsuru, T.; Uchiyama, Y.; Umana, G.; Umetsu, Y.; Upadhya,
S. S.; Uslenghi, M.; Vagelli, V.; Vagnetti, F.; Valdes-Galicia, J.;
Valentino, M.; Vallania, P.; Valore, L.; van Driel, W.; van Eldik,
C.; van Soelen, B.; Vandenbroucke, J.; Vanderwalt, J.; Vasileiadis,
G.; Vassiliev, V.; Vázquez, J. R.; Vázquez Acosta, M. L.; Vecchi,
M.; Vega, A.; Vegas, I.; Veitch, P.; Venault, P.; Venema, L.; Venter,
C.; Vercellone, S.; Vergani, S.; Verma, K.; Verzi, V.; Vettolani,
G. P.; Veyssiere, C.; Viana, A.; Viaux, N.; Vicha, J.; Vigorito,
C.; Vincent, P.; Vincent, S.; Vink, J.; Vittorini, V.; Vlahakis, N.;
Vlahos, L.; Voelk, H.; Voisin, V.; Vollhardt, A.; Volpicelli, A.; von
Brand, H.; Vorobiov, S.; Vovk, I.; Vrastil, M.; Vu, L. V.; Vuillaume,
T.; Wagner, R.; Wagner, R.; Wagner, S. J.; Wakely, S. P.; Walstra, T.;
Walter, R.; Walther, T.; Ward, J. E.; Ward, M.; Warda, K.; Warren,
D.; Wassberg, S.; Watson, J. J.; Wawer, P.; Wawrzaszek, R.; Webb,
N.; Wegner, P.; Weiner, O.; Weinstein, A.; Wells, R.; Werner, F.;
Wetteskind, H.; White, M.; White, R.; Więcek, M.; Wierzcholska, A.;
Wiesand, S.; Wijers, R.; Wilcox, P.; Wild, N.; Wilhelm, A.; Wilkinson,
M.; Will, M.; Will, M.; Williams, D. A.; Williams, J. T.; Willingale,
R.; Wilson, N.; Winde, M.; Winiarski, K.; Winkler, H.; Winter, M.;
Wischnewski, R.; Witt, E.; Wojcik, P.; Wolf, D.; Wood, M.; Wörnlein,
A.; Wu, E.; Wu, T.; Yadav, K. K.; Yamamoto, H.; Yamamoto, T.; Yamane,
N.; Yamazaki, R.; Yanagita, S.; Yang, L.; Yelos, D.; Yoshida, A.;
Yoshida, M.; Yoshida, T.; Yoshiike, S.; Yoshikoshi, T.; Yu, P.;
Zabalza, V.; Zaborov, D.; Zacharias, M.; Zaharijas, G.; Zajczyk,
A.; Zampieri, L.; Zandanel, F.; Zanmar Sanchez, R.; Zaric, D.;
Zavrtanik, D.; Zavrtanik, M.; Zdziarski, A.; Zech, A.; Zechlin, H.;
Zhao, A.; Zhdanov, V.; Ziegler, A.; Ziemann, J.; Ziętara, K.; Zink,
A.; Ziółkowski, J.; Zitelli, V.; Zoli, A.; Zorn, J.; Żychowski, P.
2016arXiv161005151C Altcode:
List of contributions from the Cherenkov Telescope Array (CTA)
Consortium presented at the 6th International Symposium on High-Energy
Gamma-Ray Astronomy (Gamma 2016), July 11-15, 2016, in Heidelberg,
Germany.
---------------------------------------------------------
Title: Complexity methods applied to turbulence in plasma astrophysics
Authors: Vlahos, L.; Isliker, H.
2016EPJST.225..977V Altcode: 2016arXiv160300394V
In this review many of the well known tools for the analysis of
Complex systems are used in order to study the global coupling of the
turbulent convection zone with the solar atmosphere where the magnetic
energy is dissipated explosively. Several well documented observations
are not easy to interpret with the use of Magnetohydrodynamic (MHD)
and/or Kinetic numerical codes. Such observations are: (1) The size
distribution of the Active Regions (AR) on the solar surface, (2) The
fractal and multi fractal characteristics of the observed magnetograms,
(3) The Self-Organised characteristics of the explosive magnetic
energy release and (4) the very efficient acceleration of particles
during the flaring periods in the solar corona. We review briefly
the work published the last twenty five years on the above issues
and propose solutions by using methods borrowed from the analysis
of complex systems. The scenario which emerged is as follows: (a)
The fully developed turbulence in the convection zone generates and
transports magnetic flux tubes to the solar surface. Using probabilistic
percolation models we were able to reproduce the size distribution and
the fractal properties of the emerged and randomly moving magnetic flux
tubes. (b) Using a Non Linear Force Free (NLFF) magnetic extrapolation
numerical code we can explore how the emerged magnetic flux tubes
interact nonlinearly and form thin and Unstable Current Sheets (UCS)
inside the coronal part of the AR. (c) The fragmentation of the UCS
and the redistribution of the magnetic field locally, when the local
current exceeds a Critical threshold, is a key process which drives
avalanches and forms coherent structures. This local reorganization of
the magnetic field enhances the energy dissipation and influences the
global evolution of the complex magnetic topology. Using a Cellular
Automaton and following the simple rules of Self Organized Criticality
(SOC), we were able to reproduce the statistical characteristics of
the observed time series of the explosive events, (d) finally, when
the AR reaches the turbulently reconnecting state (in the language of
the SOC theory this is called SOC state) it is densely populated by UCS
which can act as local scatterers (replacing the magnetic clouds in the
Fermi scenario) and enhance dramatically the heating and acceleration
of charged particles.
---------------------------------------------------------
Title: Particle Acceleration and Heating by Turbulent Reconnection
Authors: Vlahos, Loukas; Pisokas, Theophilos; Isliker, Heinz; Tsiolis,
Vassilis; Anastasiadis, Anastasios
2016ApJ...827L...3V Altcode: 2016arXiv160405234V
Turbulent flows in the solar wind, large-scale current sheets, multiple
current sheets, and shock waves lead to the formation of environments
in which a dense network of current sheets is established and sustains
“turbulent reconnection.” We constructed a 2D grid on which a number
of randomly chosen grid points are acting as scatterers (I.e., magnetic
clouds or current sheets). Our goal is to examine how test particles
respond inside this large-scale collection of scatterers. We study
the energy gain of individual particles, the evolution of their energy
distribution, and their escape time distribution. We have developed a
new method to estimate the transport coefficients from the dynamics
of the interaction of the particles with the scatterers. Replacing
the “magnetic clouds” with current sheets, we have proven that the
energization processes can be more efficient depending on the strength
of the effective electric fields inside the current sheets and their
statistical properties. Using the estimated transport coefficients
and solving the Fokker-Planck (FP) equation, we can recover the energy
distribution of the particles only for the stochastic Fermi process. We
have shown that the evolution of the particles inside a turbulent
reconnecting volume is not a solution of the FP equation, since the
interaction of the particles with the current sheets is “anomalous,”
in contrast to the case of the second-order Fermi process.
---------------------------------------------------------
Title: The Major Geoeffective Solar Eruptions of 2012 March 7:
Comprehensive Sun-to-Earth Analysis
Authors: Patsourakos, S.; Georgoulis, M. K.; Vourlidas, A.; Nindos,
A.; Sarris, T.; Anagnostopoulos, G.; Anastasiadis, A.; Chintzoglou,
G.; Daglis, I. A.; Gontikakis, C.; Hatzigeorgiu, N.; Iliopoulos, A. C.;
Katsavrias, C.; Kouloumvakos, A.; Moraitis, K.; Nieves-Chinchilla, T.;
Pavlos, G.; Sarafopoulos, D.; Syntelis, P.; Tsironis, C.; Tziotziou,
K.; Vogiatzis, I. I.; Balasis, G.; Georgiou, M.; Karakatsanis, L. P.;
Malandraki, O. E.; Papadimitriou, C.; Odstrčil, D.; Pavlos, E. G.;
Podlachikova, O.; Sandberg, I.; Turner, D. L.; Xenakis, M. N.; Sarris,
E.; Tsinganos, K.; Vlahos, L.
2016ApJ...817...14P Altcode:
During the interval 2012 March 7-11 the geospace experienced a
barrage of intense space weather phenomena including the second
largest geomagnetic storm of solar cycle 24 so far. Significant
ultra-low-frequency wave enhancements and relativistic-electron dropouts
in the radiation belts, as well as strong energetic-electron injection
events in the magnetosphere were observed. These phenomena were
ultimately associated with two ultra-fast (>2000 km s<SUP>-1</SUP>)
coronal mass ejections (CMEs), linked to two X-class flares launched
on early 2012 March 7. Given that both powerful events originated from
solar active region NOAA 11429 and their onsets were separated by less
than an hour, the analysis of the two events and the determination
of solar causes and geospace effects are rather challenging. Using
satellite data from a flotilla of solar, heliospheric and magnetospheric
missions a synergistic Sun-to-Earth study of diverse observational
solar, interplanetary and magnetospheric data sets was performed. It was
found that only the second CME was Earth-directed. Using a novel method,
we estimated its near-Sun magnetic field at 13 R<SUB>⊙</SUB> to be
in the range [0.01, 0.16] G. Steep radial fall-offs of the near-Sun
CME magnetic field are required to match the magnetic fields of the
corresponding interplanetary CME (ICME) at 1 AU. Perturbed upstream
solar-wind conditions, as resulting from the shock associated with the
Earth-directed CME, offer a decent description of its kinematics. The
magnetospheric compression caused by the arrival at 1 AU of the shock
associated with the ICME was a key factor for radiation-belt dynamics.
---------------------------------------------------------
Title: CTA Contributions to the 34th International Cosmic Ray
Conference (ICRC2015)
Authors: CTA Consortium, The; :; Abchiche, A.; Abeysekara, U.; Abril,
Ó.; Acero, F.; Acharya, B. S.; Actis, M.; Agnetta, G.; Aguilar,
J. A.; Aharonian, F.; Akhperjanian, A.; Albert, A.; Alcubierre,
M.; Alfaro, R.; Aliu, E.; Allafort, A. J.; Allan, D.; Allekotte,
I.; Aloisio, R.; Amans, J. -P.; Amato, E.; Ambrogi, L.; Ambrosi, G.;
Ambrosio, M.; Anderson, J.; Anduze, M.; Angüner, E. O.; Antolini, E.;
Antonelli, L. A.; Antonucci, M.; Antonuccio, V.; Antoranz, P.; Aramo,
C.; Aravantinos, A.; Argan, A.; Armstrong, T.; Arnaldi, H.; Arnold, L.;
Arrabito, L.; Arrieta, M.; Arrieta, M.; Asano, K.; Asorey, H. G.; Aune,
T.; Singh, C. B.; Babic, A.; Backes, M.; Bais, A.; Bajtlik, S.; Balazs,
C.; Balbo, M.; Balis, D.; Balkowski, C.; Ballester, O.; Ballet, J.;
Balzer, A.; Bamba, A.; Bandiera, R.; Barber, A.; Barbier, C.; Barceló,
M.; Barnacka, A.; Barres de Almeida, U.; Barrio, J. A.; Basso, S.;
Bastieri, D.; Bauer, C.; Baushev, A.; Becciani, U.; Becherini, Y.;
Becker Tjus, J.; Beckmann, V.; Bednarek, W.; Benbow, W.; Benedico
Ventura, D.; Berdugo, J.; Berge, D.; Bernardini, E.; Bernhard, S.;
Bernlöhr, K.; Bertucci, B.; Besel, M. -A.; Bhatt, N.; Bhattacharjee,
P.; Bhattachryya, S.; Biasuzzi, B.; Bicknell, G.; Bigongiari, C.;
Biland, A.; Billotta, S.; Bilnik, W.; Biondo, B.; Bird, T.; Birsin,
E.; Bissaldi, E.; Biteau, J.; Bitossi, M.; Blanch Bigas, O.; Blasi,
P.; Boehm, C.; Bogacz, L.; Bogdan, M.; Bohacova, M.; Boisson, C.;
Boix Gargallo, J.; Bolmont, J.; Bonanno, G.; Bonardi, A.; Bonifacio,
P.; Bonnoli, G.; Borkowski, J.; Bose, R.; Bosnjak, Z.; Bottani, A.;
Böttcher, M.; Bousquet, J. -J.; Boutonnet, C.; Bouyjou, F.; Braiding,
C.; Brandt, L.; Brau-Nogué, S.; Bregeon, J.; Bretz, T.; Briggs,
M.; Brigida, M.; Bringmann, T.; Brisken, W.; Brocato, E.; Brook, P.;
Brown, A. M.; Brun, P.; Brunetti, G.; Brunetti, L.; Bruno, P.; Bryan,
M.; Buanes, T.; Bucciantini, N.; Buchholtz, G.; Buckley, J.; Bugaev,
V.; Bühler, R.; Bulgarelli, A.; Bulik, T.; Burton, M.; Burtovoi, A.;
Busetto, G.; Buson, S.; Buss, J.; Byrum, K.; Cameron, R.; Camprecios,
J.; Canelli, F.; Canestrari, R.; Cantu, S.; Capalbi, M.; Capasso, M.;
Capobianco, G.; Caraveo, P.; Cardenzana, J.; Carius, S.; Carlile, C.;
Carmona, E.; Carosi, A.; Carosi, R.; Carr, J.; Carroll, M.; Carter,
J.; Carton, P. -H.; Caruso, R.; Casandjian, J. -M.; Casanova, S.;
Cascone, E.; Casiraghi, M.; Castellina, A.; Catalano, O.; Catalanotti,
S.; Cavazzani, S.; Cazaux, S.; Cefalà, M.; Cerchiara, P.; Cereda,
M.; Cerruti, M.; Chabanne, E.; Chadwick, P.; Champion, C.; Chaty,
S.; Chaves, R.; Cheimets, P.; Chen, A.; Chen, X.; Chernyakova, M.;
Chiappetti, L.; Chikawa, M.; Chinn, D.; Chitnis, V. R.; Cho, N.;
Christov, A.; Chudoba, J.; Cieślar, M.; Cillis, A.; Ciocci, M. A.;
Clay, R.; Cohen-Tanugi, J.; Colafrancesco, S.; Colin, P.; Colombo,
E.; Colome, J.; Colonges, S.; Compin, M.; Conforti, V.; Connaughton,
V.; Connell, S.; Conrad, J.; Contreras, J. L.; Coppi, P.; Corbel, S.;
Coridian, J.; Corona, P.; Corti, D.; Cortina, J.; Cossio, L.; Costa,
A.; Costantini, H.; Cotter, G.; Courty, B.; Covino, S.; Covone, G.;
Crimi, G.; Criswell, S. J.; Crocker, R.; Croston, J.; Cusumano, G.;
Da Vela, P.; Dale, Ø.; D'Ammando, F.; Dang, D.; Daniel, M.; Davids,
I.; Dawson, B.; Dazzi, F.; de Aguiar Costa, B.; De Angelis, A.; de
Araujo Cardoso, R. F.; De Caprio, V.; De Cesare, G.; De Franco, A.;
De Frondat, F.; de Gouveia Dal Pino, E. M.; de la Calle, I.; De La
Vega, G. A.; de los Reyes Lopez, R.; De Lotto, B.; De Luca, A.; de
Mello Neto, J. R. T.; de Naurois, M.; de Oña Wilhelmi, E.; De Palma,
F.; de Souza, V.; Decock, G.; Deil, C.; Del Santo, M.; Delagnes, E.;
Deleglise, G.; Delgado, C.; della Volpe, D.; Deloye, P.; Depaola, G.;
Detournay, M.; Dettlaff, A.; Di Girolamo, T.; Di Giulio, C.; Di Paola,
A.; Di Pierro, F.; Di Sciascio, G.; Díaz, C.; Dick, J.; Dickinson, H.;
Diebold, S.; Diez, V.; Digel, S.; Dipold, J.; Disset, G.; Distefano,
A.; Djannati-Ataï, A.; Doert, M.; Dohmke, M.; Domainko, W.; Dominik,
N.; Dominis Prester, D.; Donat, A.; Donnarumma, I.; Dorner, D.; Doro,
M.; Dournaux, J. -L.; Doyle, K.; Drake, G.; Dravins, D.; Drury, L.;
Dubus, G.; Dumas, D.; Dumm, J.; Durand, D.; D'Urso, D.; Dwarkadas,
V.; Dyks, J.; Dyrda, M.; Ebr, J.; Echaniz, J. C.; Edy, E.; Egberts,
K.; Egberts, K.; Eger, P.; Einecke, S.; Eisch, J.; Eisenkolb, F.;
Eleftheriadis, C.; Elsässer, D.; Emmanoulopoulos, D.; Engelbrecht,
C.; Engelhaupt, D.; Ernenwein, J. -P.; Errando, M.; Eschbach, S.;
Etchegoyen, A.; Evans, P.; Fairbairn, M.; Falcone, A.; Fantinel, D.;
Farakos, K.; Farnier, C.; Farrell, E.; Farrell, S.; Fasola, G.; Fegan,
S.; Feinstein, F.; Ferenc, D.; Fernandez, A.; Fernandez-Alonso, M.;
Ferreira, O.; Fesquet, M.; Fetfatzis, P.; Fiasson, A.; Filipčič, A.;
Filipovic, M.; Fink, D.; Finley, C.; Finley, J. P.; Finoguenov, A.;
Fioretti, V.; Fiorini, M.; Firpo Curcoll, R.; Fleischhack, H.; Flores,
H.; Florin, D.; Föhr, C.; Fokitis, E.; Font, L.; Fontaine, G.; Fontes,
B.; Forest, F.; Fornasa, M.; Förster, A.; Fortin, P.; Fortson, L.;
Fouque, N.; Franckowiak, A.; Franco, F. J.; Frankowski, A.; Frega,
N.; Freire Mota Albuquerque, I.; Freixas Coromina, L.; Fresnillo,
L.; Fruck, C.; Fuessling, M.; Fugazza, D.; Fujita, Y.; Fukami, S.;
Fukazawa, Y.; Fukuda, T.; Fukui, Y.; Funk, S.; Gäbele, W.; Gabici,
S.; Gadola, A.; Galante, N.; Gall, D. D.; Gallant, Y.; Galloway, D.;
Gallozzi, S.; Gao, S.; Garcia, B.; García Gil, R.; Garcia López,
R.; Garczarczyk, M.; Gardiol, D.; Gargano, C.; Gargano, F.; Garozzo,
S.; Garrecht, F.; Garrido, D.; Garrido, L.; Gascon, D.; Gaskins,
J.; Gaudemard, J.; Gaug, M.; Gaweda, J.; Geffroy, N.; Gérard, L.;
Ghalumyan, A.; Ghedina, A.; Ghigo, M.; Ghislain, P.; Giannakaki, E.;
Gianotti, F.; Giarrusso, S.; Giavitto, G.; Giebels, B.; Giglietto,
N.; Gika, V.; Gimenes, R.; Giomi, M.; Giommi, P.; Giordano, F.;
Giovannini, G.; Giro, E.; Giroletti, M.; Giuliani, A.; Glicenstein,
J. -F.; Godinovic, N.; Goldoni, P.; Gomez Berisso, M.; Gomez Vargas,
G. A.; Gonzalez, M. M.; González, A.; González, F.; González
Muñoz, A.; Gothe, K. S.; Gotz, D.; Grabarczyk, T.; Graciani, R.;
Grandi, P.; Grañena, F.; Granot, J.; Grasseau, G.; Gredig, R.;
Green, A. J.; Green, A. M.; Greenshaw, T.; Grenier, I.; Grillo, A.;
Grondin, M. -H.; Grube, J.; Grudzinska, M.; Grygorczuk, J.; Guarino,
V.; Guberman, D.; Gunji, S.; Gyuk, G.; Hadasch, D.; Hagedorn, A.;
Hahn, J.; Hakansson, N.; Hamer Heras, N.; Hanabata, Y.; Hara, S.;
Hardcastle, M. J.; Harris, J.; Hassan, T.; Hatanaka, K.; Haubold,
T.; Haupt, A.; Hayakawa, T.; Hayashida, M.; Heller, M.; Heller, R.;
Henault, F.; Henri, G.; Hermann, G.; Hermel, R.; Herrera Llorente, J.;
Herrero, A.; Hervet, O.; Hidaka, N.; Hinton, J.; Hirai, W.; Hirotani,
K.; Hoard, D.; Hoffmann, D.; Hofmann, W.; Hofverberg, P.; Holch, T.;
Holder, J.; Hooper, S.; Horan, D.; Hörandel, J. R.; Hormigos, S.;
Horns, D.; Hose, J.; Houles, J.; Hovatta, T.; Hrabovsky, M.; Hrupec,
D.; Huet, J. -M.; Hütten, M.; Humensky, T. B.; Huovelin, J.; Huppert,
J. -F.; Iacovacci, M.; Ibarra, A.; Idźkowski, B.; Ikawa, D.; Illa,
J. M.; Impiombato, D.; Incorvaia, S.; Inome, Y.; Inoue, S.; Inoue,
T.; Inoue, Y.; Iocco, F.; Ioka, K.; Iori, M.; Ishio, K.; Israel,
G. L.; Jablonski, C.; Jacholkowska, A.; Jacquemier, J.; Jamrozy,
M.; Janecek, P.; Janiak, M.; Jankowsky, F.; Jean, P.; Jeanney, C.;
Jegouzo, I.; Jenke, P.; Jimenez, J. J.; Jingo, M.; Jingo, M.; Jocou,
L.; Jogler, T.; Johnson, C. A.; Journet, L.; Juffroy, C.; Jung,
I.; Kaaret, P. E.; Kagaya, M.; Kakuwa, J.; Kalekin, O.; Kalkuhl, C.;
Kankanyan, R.; Karastergiou, A.; Kärcher, K.; Karczewski, M.; Karkar,
S.; Karn, P.; Kasperek, J.; Katagiri, H.; Kataoka, J.; Katarzyński,
K.; Katz, U.; Kaufmann, S.; Kawanaka, N.; Kawashima, T.; Kazanas,
D.; Kelley-Hoskins, N.; Kellner-Leidel, B.; Kendziorra, E.; Kersten,
J.; Khélifi, B.; Kieda, D. B.; Kihm, T.; Kisaka, S.; Kissmann, R.;
Klepser, S.; Kluźniak, W.; Knapen, J.; Knapp, J.; Knödlseder, J.;
Köck, F.; Kocot, J.; Kodakkadan, A.; Kodani, K.; Kohri, K.; Kojima,
T.; Kokkotas, K.; Kolitzus, D.; Komin, N.; Kominis, I.; Konno, Y.;
Kosack, K.; Koss, G.; Koul, R.; Kowal, G.; Koyama, S.; Kozioł,
J.; Kraus, M.; Krause, J.; Krause, M.; Krawzcynski, H.; Krennrich,
F.; Kretzschmann, A.; Kruger, P.; Kubo, H.; Kudryavtsev, V.; Kukec
Mezek, G.; Kushida, J.; Kuznetsov, A.; La Barbera, A.; La Palombara,
N.; La Parola, V.; La Rosa, G.; Laffon, H.; Lagadec, T.; Lahmann,
R.; Lalik, K.; Lamanna, G.; Landriu, D.; Landt, H.; Lang, R. G.;
Languignon, D.; Lapington, J.; Laporte, P.; Latovski, N.; Law-Green,
D.; Le Fèvre, J. -P.; Le Flour, T.; Le Sidaner, P.; Lee, S. -H.; Lee,
W. H.; Leffhalm, K.; Leich, H.; Leigui de Oliveira, M. A.; Lelas,
D.; Lemière, A.; Lemoine-Goumard, M.; Lenain, J. -P.; Leonard, R.;
Leoni, R.; Lessio, L.; Leto, G.; Leveque, A.; Lieunard, B.; Limon,
M.; Lindemann, R.; Lindfors, E.; Liolios, A.; Lipniacka, A.; Lockart,
H.; Lohse, T.; Loiseau, D.; Łokas, E.; Lombardi, S.; Longo, F.;
Longo, G.; Lopatin, A.; Lopez, M.; López-Coto, R.; López-Oramas,
A.; Loreggia, D.; Louge, T.; Louis, F.; Lu, C. -C.; Lucarelli, F.;
Lucchesi, D.; Lüdecke, H.; Luque-Escamilla, P. L.; Luz, O.; Lyard,
E.; Maccarone, M. C.; Maccarone, T. J.; Mach, E.; Madejski, G. M.;
Madonna, A.; Mahabir, M.; Maier, G.; Majumdar, P.; Makariev, M.;
Malaguti, G.; Malaspina, G.; Mallot, A. K.; Maltezos, S.; Mancilla,
A.; Mandat, D.; Maneva, G.; Manigot, P.; Mankushiyil, N.; Mannheim,
K.; Maragos, N.; Marano, D.; Marchegiani, P.; Marcomini, J. A.;
Marcowith, A.; Mariotti, M.; Marisaldi, M.; Markoff, S.; Marszałek,
A.; Martens, C.; Martí, J.; Martin, J. -M.; Martin, P.; Martínez, G.;
Martínez, M.; Martínez, O.; Marx, R.; Massimino, P.; Mastichiadis,
A.; Mastroianni, S.; Mastropietro, M.; Masuda, S.; Matsumoto, H.;
Matsuoka, S.; Mattiazzo, S.; Maurin, G.; Maxted, N.; Maya, J.; Mayer,
M.; Mazin, D.; Mazureau, E.; Mazziotta, M. N.; Mc Comb, L.; McCann,
A.; McCubbin, N.; McHardy, I.; McKay, R.; McKinney, K.; Meagher, K.;
Medina, C.; Mehrez, F.; Melioli, C.; Melkumyan, D.; Melo, D.; Melse,
T.; Mereghetti, S.; Mertsch, P.; Meyer, M.; Meyrelles, J. L., jr;
Miccichè, A.; Michałowski, J.; Micolon, P.; Mientjes, P.; Mignot,
S.; Mihailidis, A.; Mineo, T.; Minuti, M.; Mirabal, N.; Mirabel, F.;
Miranda, J. M.; Mirzoyan, R.; Mistò, A.; Mitchell, A.; Mizuno, T.;
Moderski, R.; Mognet, I.; Mohammed, M.; Moharana, R.; Molinari, E.;
Monmarthe, E.; Monnier, G.; Montaruli, T.; Monte, C.; Monteiro, I.;
Moore, P.; Moralejo Olaizola, A.; Morello, C.; Moretti, E.; Mori,
K.; Morlino, G.; Morselli, A.; Mottez, F.; Moudden, Y.; Moulin, E.;
Mrusek, I.; Mueller, S.; Mukherjee, R.; Munar-Adrover, P.; Mundell,
C.; Muraishi, H.; Murase, K.; Muronga, A.; Murphy, A.; Nagataki,
S.; Nagayoshi, T.; Nagesh, B. K.; Naito, T.; Nakajima, D.; Nakamori,
T.; Nakayama, K.; Naumann, D.; Nayman, P.; Nellen, L.; Nemmen, R.;
Neronov, A.; Neustroev, V.; Neyroud, N.; Nguyen, T.; Nicastro,
L.; Nicolau-Kukliński, J.; Niederwanger, F.; Niedźwiecki, A.;
Niemiec, J.; Nieto, D.; Nievas, M.; Nikolaidis, A.; Nishijima, K.;
Nishikawa, K. -I.; Noda, K.; Nogues, L.; Nolan, S.; Northrop, R.;
Nosek, D.; Nozka, L.; Nunio, F.; Oakes, L.; O'Brien, P.; Occhipinti,
G.; O'Faolain de Bhroithe, A.; Ogino, M.; Ohira, Y.; Ohishi, M.; Ohm,
S.; Ohoka, H.; Okumura, A.; Olive, J. -F.; Olszowski, D.; Ong, R. A.;
Ono, S.; Orienti, M.; Orito, R.; Orlati, A.; Orlati, A.; Osborne, J.;
Ostrowski, M.; Otero, L. A.; Ottaway, D.; Otte, N.; Oya, I.; Ozieblo,
A.; Padovani, M.; Pagano, I.; Paiano, S.; Paizis, A.; Palacio, J.;
Palatka, M.; Pallotta, J.; Panagiotidis, K.; Panazol, J. -L.; Paneque,
D.; Panter, M.; Panzera, M. R.; Paoletti, R.; Paolillo, M.; Papayannis,
A.; Papyan, G.; Paravac, A.; Paredes, J. M.; Pareschi, G.; Park, N.;
Parsons, D.; Paśko, P.; Pavy, S.; Arribas, M. Paz; Pech, M.; Peck,
A.; Pedaletti, G.; Peet, S.; Pelassa, V.; Pelat, D.; Peres, C.;
Perez, M. d. C.; Perri, L.; Persic, M.; Petrashyk, A.; Petrucci,
P. -O.; Peyaud, B.; Pfeifer, M.; Pfeiffer, G.; Piano, G.; Pichel,
A.; Pieloth, D.; Pierbattista, M.; Pierre, E.; Pinto de Pinho, F.;
García, C. Pio; Piret, Y.; Pita, S.; Planes, A.; Platino, M.; Platos,
Ł.; Platzer, R.; Podkladkin, S.; Pogosyan, L.; Pohl, M.; Poinsignon,
P.; Ponz, J. D.; Porcelli, A.; Potter, W.; Poulios, S.; Poutanen,
J.; Prandini, E.; Prast, J.; Preece, R.; Profeti, F.; Prokhorov, D.;
Prokoph, H.; Prouza, M.; Proyetti, M.; Pruchniewicz, R.; Pueschel,
E.; Pühlhofer, G.; Puljak, I.; Punch, M.; Pyzioł, R.; Queiroz,
F.; Quel, E. J.; Quinn, J.; Quirrenbach, A.; Racero, E.; Räck,
T.; Rafalski, J.; Rafighi, I.; Rainò, S.; Rajda, P. J.; Rameez, M.;
Rando, R.; Rannot, R. C.; Rataj, M.; Rateau, S.; Ravel, T.; Ravignani,
D.; Razzaque, S.; Reardon, P.; Reimann, O.; Reimer, A.; Reimer, O.;
Reitberger, K.; Renaud, M.; Renner, S.; Reposeur, T.; Rettig, R.;
Reville, B.; Rhode, W.; Ribeiro, D.; Ribó, M.; Richards, G.; Richer,
M. G.; Rico, J.; Ridky, J.; Rieger, F.; Ringegni, P.; Ristori, P. R.;
Rivière, A.; Rivoire, S.; Roache, E.; Rodeghiero, G.; Rodriguez,
J.; Rodriguez Fernandez, G.; Rodríguez Vázquez, J. J.; Rogers, T.;
Rojas, G.; Romano, P.; Romay Rodriguez, M. P.; Romeo, G.; Romero,
G. E.; Roncadelli, M.; Rose, J.; Rosen, S.; Rosier Lees, S.; Ross,
D.; Rossiter, P.; Rouaix, G.; Rousselle, J.; Rovero, A. C.; Rowell,
G.; Roy, F.; Royer, S.; Różańska, A.; Rudak, B.; Rugliancich,
A.; Rulten, C.; Rupiński, M.; Russo, F.; Rutkowski, K.; Saavedra,
O.; Sabatini, S.; Sacco, B.; Saemann, E. O.; Saggion, A.; Saha, L.;
Sahakian, V.; Saito, K.; Saito, T.; Sakaki, N.; Salega, M.; Salek, D.;
Salgado, J.; Salini, A.; Sanchez, D.; Sanchez, F.; Sanchez-Conde, M.;
Sandaker, H.; Sandoval, A.; Sangiorgi, P.; Sanguillon, M.; Sano, H.;
Santander, M.; Santangelo, A.; Santos, E. M.; Santos-Lima, R.; Sanuy,
A.; Sapozhnikov, L.; Sarkar, S.; Satalecka, K.; Savalle, R.; Sawada,
M.; Sayède, F.; Schafer, J.; Schanne, S.; Schanz, T.; Schioppa, E. J.;
Schlenstedt, S.; Schlickeiser, R.; Schmidt, T.; Schmoll, J.; Schneider,
M.; Schovanek, P.; Schubert, A.; Schultz, C.; Schultze, J.; Schulz,
A.; Schulz, S.; Schure, K.; Schussler, F.; Schwab, T.; Schwanke, U.;
Schwarz, J.; Schweizer, T.; Schwemmer, S.; Schwendicke, U.; Schwerdt,
C.; Segreto, A.; Seiradakis, J. -H.; Sembroski, G. H.; Semikoz, D.;
Serre, N.; Servillat, M.; Seweryn, K.; Shafi, N.; Sharma, M.; Shayduk,
M.; Shellard, R. C.; Shibata, T.; Shiningayamwe Pandeni, K.; Shukla,
A.; Shum, E.; Sidoli, L.; Sidz, M.; Sieiro, J.; Siejkowski, H.; Silk,
J.; Sillanpää, A.; Simone, D.; Singh, B. B.; Sinha, A.; Sironi, G.;
Sitarek, J.; Sizun, P.; Slyusar, V.; Smith, A.; Smith, J.; Sobczyńska,
D.; Sol, H.; Sottile, G.; Sowiński, M.; Spanier, F.; Spengler, G.;
Spiga, D.; Stadler, R.; Stahl, O.; Stamatescu, V.; Stamerra, A.;
Stanič, S.; Starling, R.; Stawarz, Ł.; Steenkamp, R.; Stefanik, S.;
Stegmann, C.; Steiner, S.; Stella, C.; Stergioulas, N.; Sternberger,
R.; Sterzel, M.; Stevenson, B.; Stinzing, F.; Stodulska, M.; Stodulski,
M.; Stolarczyk, T.; Straumann, U.; Strazzeri, E.; Stringhetti, L.;
Strzys, M.; Stuik, R.; Sulanke, K. -H.; Supanitsky, A. D.; Suric, T.;
Sushch, I.; Sutcliffe, P.; Sykes, J.; Szanecki, M.; Szepieniec, T.;
Szwarnog, P.; Tacchini, A.; Tachihara, K.; Tagliaferri, G.; Tajima, H.;
Takahashi, H.; Takahashi, K.; Takahashi, M.; Takalo, L.; Takami, H.;
Talbot, G.; Tammi, J.; Tanaka, M.; Tanaka, S.; Tanaka, T.; Tanaka, Y.;
Tanci, C.; Tarantino, E.; Tavani, M.; Tavecchio, F.; Tavernet, J. -P.;
Tayabaly, K.; Tejedor, L. A.; Telezhinsky, I.; Temme, F.; Temnikov, P.;
Tenzer, C.; Terada, Y.; Terrier, R.; Tescaro, D.; Teshima, M.; Testa,
V.; Tezier, D.; Thayer, J.; Thomas, V.; Thornhill, J.; Thuermann,
D.; Tibaldo, L.; Tibolla, O.; Tiengo, A.; Tijsseling, G.; Timpanaro,
M. C.; Tluczykont, M.; Todero Peixoto, C. J.; Tokanai, F.; Tokarz, M.;
Toma, K.; Toma, K.; Tomastik, J.; Tomono, Y.; Tonachini, A.; Tonev,
D.; Torii, K.; Tornikoski, M.; Torres, D. F.; Torres, M.; Torresi, E.;
Toscano, S.; Toso, G.; Tosti, G.; Totani, T.; Tothill, N.; Toussenel,
F.; Tovmassian, G.; Townsley, C.; Toyama, T.; Travnicek, P.; Trifoglio,
M.; Troyano Pujadas, I.; Troyano Pujadas, I.; Trzeciak, M.; Tsinganos,
K.; Tsubone, Y.; Tsuchiya, Y.; Tsujimoto, S.; Tsuru, T.; Uchiyama, Y.;
Umana, G.; Umetsu, Y.; Underwood, C.; Upadhya, S. S.; Uslenghi, M.;
Vagnetti, F.; Valdes-Galicia, J.; Vallania, P.; Vallejo, G.; Valore,
L.; van Driel, W.; van Eldik, C.; van Soelen, B.; Vandenbroucke, J.;
Vanderwalt, J.; Vasileiadis, G.; Vassiliev, V.; Vázquez Acosta,
M. L.; Vecchi, M.; Vegas, I.; Veitch, P.; Venema, L.; Venter, C.;
Vercellone, S.; Vergani, S.; Verma, K.; Verzi, V.; Vettolani, G. P.;
Viana, A.; Vicha, J.; Videla, M.; Vigorito, C.; Vincent, P.; Vincent,
S.; Vink, J.; Vittorini, V.; Vlahakis, N.; Vlahos, L.; Voelk, H.;
Vogler, P.; Voisin, V.; Vollhardt, A.; Volpicelli, A.; Vorobiov,
S.; Vovk, I.; Vu, L. V.; Wagner, R.; Wagner, R. M.; Wagner, R. G.;
Wagner, S. J.; Wakely, S. P.; Walter, R.; Walther, T.; Ward, J. E.;
Ward, M.; Warda, K.; Warwick, R.; Wassberg, S.; Watson, J.; Wawer,
P.; Wawrzaszek, R.; Webb, N.; Wegner, P.; Weinstein, A.; Weitzel, Q.;
Wells, R.; Werner, F.; Werner, M.; Wetteskind, H.; White, M.; White,
R.; Więcek, M.; Wierzcholska, A.; Wiesand, S.; Wijers, R.; Wild, N.;
Wilhelm, A.; Wilkinson, M.; Will, M.; Williams, D. A.; Williams, J. T.;
Willingale, R.; Winde, M.; Winiarski, K.; Winkler, H.; Wischnewski,
R.; Wojcik, P.; Wolf, D.; Wood, M.; Wörnlein, A.; Wu, E.; Wu, T.;
Yadav, K. K.; Yamamoto, H.; Yamamoto, T.; Yamazaki, R.; Yanagita, S.;
Yang, L.; Yebras, J. M.; Yelos, D.; Yeung, W.; Yoshida, A.; Yoshida,
T.; Yoshiike, S.; Yoshikoshi, T.; Yu, P.; Zabalza, V.; Zabalza, V.;
Zacharias, M.; Zaharijas, G.; Zajczyk, A.; Zampieri, L.; Zandanel,
F.; Zanin, R.; Zanmar Sanchez, R.; Zavrtanik, D.; Zavrtanik, M.;
Zdziarski, A.; Zech, A.; Zechlin, H.; Zhao, A.; Ziegler, A.; Ziemann,
J.; Ziętara, K.; Ziółkowski, J.; Zitelli, V.; Zoli, A.; Zurbach,
C.; Żychowski, P.
2015arXiv150805894C Altcode:
List of contributions from the CTA Consortium presented at the 34th
International Cosmic Ray Conference, 30 July - 6 August 2015, The Hague,
The Netherlands.
---------------------------------------------------------
Title: Particle acceleration in regions of magnetic flux emergence:
a statistical approach using test-particle- and MHD-simulations
Authors: Vlahos, Loukas; Archontis, Vasilis; Isliker, Heinz
2014cosp...40E3539V Altcode:
We consider 3D nonlinear MHD simulations of an emerging flux tube, from
the convection zone into the corona, focusing on the coronal part of
the simulations. We first analyze the statistical nature and spatial
structure of the electric field, calculating histograms and making
use of iso-contour visualizations. Then test-particle simulations are
performed for electrons, in order to study heating and acceleration
phenomena, as well as to determine HXR emission. This study is done by
comparatively exploring quiet, turbulent explosive, and mildly explosive
phases of the MHD simulations. Also, the importance of collisional and
relativistic effects is assessed, and the role of the integration time
is investigated. Particular aim of this project is to verify the quasi-
linear assumptions made in standard transport models, and to identify
possible transport effects that cannot be captured with the latter. In
order to determine the relation of our results to Fermi acceleration
and Fokker-Planck modeling, we determine the standard transport
coefficients. After all, we find that the electric field of the MHD
simulations must be downscaled in order to prevent an un-physically
high degree of acceleration, and the value chosen for the scale factor
strongly affects the results. In different MHD time-instances we find
heating to take place, and acceleration that depends on the level of
MHD turbulence. Also, acceleration appears to be a transient phenomenon,
there is a kind of saturation effect, and the parallel dynamics clearly
dominate the energetics. The HXR spectra are not yet really compatible
with observations, we have though to further explore the scaling of
the electric field and the integration times used.
---------------------------------------------------------
Title: Particle acceleration in solar active regions being in the
state of self-organized criticality.
Authors: Vlahos, Loukas
2014cosp...40E3540V Altcode:
We review the recent observational results on flare initiation and
particle acceleration in solar active regions. Elaborating a statistical
approach to describe the spatiotemporally intermittent electric field
structures formed inside a flaring solar active region, we investigate
the efficiency of such structures in accelerating charged particles
(electrons and protons). The large-scale magnetic configuration in the
solar atmosphere responds to the strong turbulent flows that convey
perturbations across the active region by initiating avalanche-type
processes. The resulting unstable structures correspond to small-scale
dissipation regions hosting strong electric fields. Previous research
on particle acceleration in strongly turbulent plasmas provides
a general framework for addressing such a problem. This framework
combines various electromagnetic field configurations obtained by
magnetohydrodynamical (MHD) or cellular automata (CA) simulations, or
by employing a statistical description of the field’s strength and
configuration with test particle simulations. We work on data-driven 3D
magnetic field extrapolations, based on a self-organized criticality
models (SOC). A relativistic test-particle simulation traces each
particle’s guiding center within these configurations. Using the
simulated particle-energy distributions we test our results against
observations, in the framework of the collisional thick target model
(CTTM) of solar hard X-ray (HXR) emission and compare our results with
the current observations.
---------------------------------------------------------
Title: A statistical study of current-sheet formation above solar
active regions based on selforganized criticality
Authors: Dimitropoulou, M.; Isliker, H.; Vlahos, L.; Georgoulis, M.;
Anastasiadis, A.; Toutountzi, A.
2013hell.conf...16D Altcode:
We treat flaring solar active regions as physical systems having
reached the self-organized critical state. Their evolving magnetic
configurations in the low corona may satisfy an instability criterion,
related to the excession of a specific threshold in the curl of the
magnetic field. This imposed instability criterion implies an almost
zero resistivity everywhere in the solar corona, except in regions where
magnetic-field discontinuities and. hence, local currents, reach the
critical value. In these areas, current-driven instabilities enhance
the resistivity by many orders of magnitude forming structures which
efficiently accelerate charged particles. Simulating the formation
of such structures (thought of as current sheets) via a refined SOC
cellular-automaton model provides interesting information regarding
their statistical properties. It is shown that the current density in
such unstable regions follows power-law scaling. Furthermore, the size
distribution of the produced current sheets is best fitted by power
laws, whereas their formation probability is investigated against
the photospheric magnetic configuration (e.g. Polarity Inversion
Lines, Plage). The average fractal dimension of the produced current
sheets is deduced depending on the selected critical threshold. The
above-mentioned statistical description of intermittent electric
field structures can be used by collisional relativistic test particle
simulations, aiming to interpret particle acceleration in flaring active
regions and in strongly turbulent media in astrophysical plasmas. The
above work is supported by the Hellenic National Space Weather Research
Network (HNSWRN) via the THALIS Programme.
---------------------------------------------------------
Title: A Data-Driven, Integrated Flare Model Based on Self-Organized
Criticality
Authors: Dimitropoulou, M.; Isliker, H.; Vlahos, L.; Georgoulis, M.
2013hell.conf....7D Altcode:
We interpret solar flares as events originating in solar active regions
having reached the self-organized critical state, by alternatively
using two versions of an "integrated flare model" - one static and
one dynamic. In both versions the initial conditions are derived
from observations aiming to investigate whether well-known scaling
laws observed in the distribution functions of characteristic flare
parameters are reproduced after the self-organized critical state
has been reached. In the static model, we first apply a nonlinear
force-free extrapolation that reconstructs the three-dimensional
magnetic fields from two-dimensional vector magnetograms. We then locate
magnetic discontinuities exceeding a threshold in the Laplacian of the
magnetic field. These discontinuities are relaxed in local diffusion
events, implemented in the form of cellular-automaton evolution
rules. Subsequent loading and relaxation steps lead the system to
self-organized criticality, after which the statistical properties of
the simulated events are examined. In the dynamic version we deploy an
enhanced driving mechanism, which utilizes the observed evolution of
active regions, making use of sequential vector magnetograms. We first
apply the static cellular automaton model to consecutive solar vector
magnetograms until the self-organized critical state is reached. We
then evolve the magnetic field inbetween these processed snapshots
through spline interpolation, acting as a natural driver in the dynamic
model. The identification of magnetically unstable sites as well as
their relaxation follow the same rules as in the static model after each
interpolation step. Subsequent interpolation/driving and relaxation
steps cover all transitions until the end of the sequence. Physical
requirements, such as the divergence-free condition for the magnetic
field vector, are approximately satisfied in both versions of the
model. We obtain robust power laws in the distribution functions of
the modelled flaring events with scaling indices in good agreement
with observations. We therefore conclude that well-known statistical
properties of flares are reproduced after active regions reach
self-organized criticality. The significant enhancement in both the
static and the dynamic integrated flare models is that they initiate
the simulation from observations, thus facilitating energy calculation
in physical units. Especially in the dynamic version of the model,
the driving of the system is based on observed, evolving vector
magnetograms, allowing for the separation between MHD and kinetic
timescales through the assignment of distinct MHD timestamps to each
interpolation step.
---------------------------------------------------------
Title: Particle Acceleration in a Statistically Modeled Solar
Active-Region Corona
Authors: Toutounzi, A.; Vlahos, L.; Isliker, H.; Dimitropoulou, M.;
Anastasiadis, A.; Georgoulis, M.
2013hell.conf....8T Altcode:
Elaborating a statistical approach to describe the spatiotemporally
intermittent electric field structures formed inside a flaring solar
active region, we investigate the efficiency of such structures
in accelerating charged particles (electrons). The large-scale
magnetic configuration in the solar atmosphere responds to the strong
turbulent flows that convey perturbations across the active region by
initiating avalanche-type processes. The resulting unstable structures
correspond to small-scale dissipation regions hosting strong electric
fields. Previous research on particle acceleration in strongly turbulent
plasmas provides a general framework for addressing such a problem. This
framework combines various electromagnetic field configurations obtained
by magnetohydrodynamical (MHD) or cellular automata (CA) simulations,
or by employing a statistical description of the field's strength
and configuration with test particle simulations. Our objective is to
complement previous work done on the subject. As in previous efforts,
a set of three probability distribution functions describes our
ad-hoc electromagnetic field configurations. In addition, we work on
data-driven 3D magnetic field extrapolations. A collisional relativistic
test-particle simulation traces each particle's guiding center
within these configurations. We also find that an interplay between
different electron populations (thermal/non-thermal, ambient/injected)
in our simulations may also address, via a re-acceleration mechanism,
the so called `number problem'. Using the simulated particle-energy
distributions at different heights of the cylinder we test our results
against observations, in the framework of the collisional thick target
model (CTTM) of solar hard X-ray (HXR) emission. The above work is
supported by the Hellenic National Space Weather Research Network
(HNSWRN) via the THALIS Programme.
---------------------------------------------------------
Title: Sun-to-Earth Analysis of a Major Geoeffective Solar Eruption
within the Framework of the
Authors: Patsourakos, S.; Vlahos, L.; Georgoulis, M.; Tziotziou,
K.; Nindos, A.; Podladchikova, O.; Vourlidas, A.; Anastasiadis, A.;
Sandberg, I.; Tsinganos, K.; Daglis, I.; Hillaris, A.; Preka-Papadema,
P.; Sarris, M.; Sarris, T.
2013hell.conf...10P Altcode:
Transient expulsions of gigantic clouds of solar coronal plasma into
the interplanetary space in the form of Coronal Mass Ejections (CMEs)
and sudden, intense flashes of electromagnetic radiation, solar flares,
are well-established drivers of the variable Space Weather. Given the
innate, intricate links and connections between the solar drivers and
their geomagnetic effects, synergistic efforts assembling all pieces
of the puzzle along the Sun-Earth line are required to advance our
understanding of the physics of Space Weather. This is precisely the
focal point of the Hellenic National Space Weather Research Network
(HNSWRN) under the THALIS Programme. Within the HNSWRN framework,
we present here the first results from a coordinated multi-instrument
case study of a major solar eruption (X5.4 and X1.3 flares associated
with two ultra-fast (>2000 km/s) CMEs) which were launched early
on 7 March 2012 and triggered an intense geomagnetic storm (min Dst
=-147 nT) approximately two days afterwards. Several elements of
the associated phenomena, such as the flare and CME, EUV wave, WL
shock, proton and electron event, interplanetary type II radio burst,
ICME and magnetic cloud and their spatiotemporal relationships and
connections are studied all way from Sun to Earth. To this end, we
make use of satellite data from a flotilla of solar, heliospheric and
magnetospheric missions and monitors (e.g., SDO, STEREO, WIND, ACE,
Herschel, Planck and INTEGRAL). We also present our first steps toward
formulating a cohesive physical scenario to explain the string of the
observables and to assess the various physical mechanisms than enabled
and gave rise to the significant geoeffectiveness of the eruption.
---------------------------------------------------------
Title: CTA contributions to the 33rd International Cosmic Ray
Conference (ICRC2013)
Authors: CTA Consortium, The; :; Abril, O.; Acharya, B. S.; Actis, M.;
Agnetta, G.; Aguilar, J. A.; Aharonian, F.; Ajello, M.; Akhperjanian,
A.; Alcubierre, M.; Aleksic, J.; Alfaro, R.; Aliu, E.; Allafort,
A. J.; Allan, D.; Allekotte, I.; Aloisio, R.; Amato, E.; Ambrosi,
G.; Ambrosio, M.; Anderson, J.; Angüner, E. O.; Antonelli, L. A.;
Antonuccio, V.; Antonucci, M.; Antoranz, P.; Aravantinos, A.; Argan,
A.; Arlen, T.; Aramo, C.; Armstrong, T.; Arnaldi, H.; Arrabito, L.;
Asano, K.; Ashton, T.; Asorey, H. G.; Aune, T.; Awane, Y.; Baba, H.;
Babic, A.; Baby, N.; Bähr, J.; Bais, A.; Baixeras, C.; Bajtlik, S.;
Balbo, M.; Balis, D.; Balkowski, C.; Ballet, J.; Bamba, A.; Bandiera,
R.; Barber, A.; Barbier, C.; Barceló, M.; Barnacka, A.; Barnstedt,
J.; Barres de Almeida, U.; Barrio, J. A.; Basili, A.; Basso, S.;
Bastieri, D.; Bauer, C.; Baushev, A.; Becciani, U.; Becerra, J.;
Becerra, J.; Becherini, Y.; Bechtol, K. C.; Becker Tjus, J.; Beckmann,
V.; Bednarek, W.; Behera, B.; Belluso, M.; Benbow, W.; Berdugo, J.;
Berge, D.; Berger, K.; Bernard, F.; Bernardino, T.; Bernlöhr, K.;
Bertucci, B.; Bhat, N.; Bhattacharyya, S.; Biasuzzi, B.; Bigongiari,
C.; Biland, A.; Billotta, S.; Bird, T.; Birsin, E.; Bissaldi, E.;
Biteau, J.; Bitossi, M.; Blake, S.; Blanch Bigas, O.; Blasi, P.;
Bobkov, A.; Boccone, V.; Böttcher, M.; Bogacz, L.; Bogart, J.;
Bogdan, M.; Boisson, C.; Boix Gargallo, J.; Bolmont, J.; Bonanno,
G.; Bonardi, A.; Bonev, T.; Bonifacio, P.; Bonnoli, G.; Bordas,
P.; Borgland, A.; Borkowski, J.; Bose, R.; Botner, O.; Bottani, A.;
Bouchet, L.; Bourgeat, M.; Boutonnet, C.; Bouvier, A.; Brau-Nogué, S.;
Braun, I.; Bretz, T.; Briggs, M.; Brigida, M.; Bringmann, T.; Britto,
R.; Brook, P.; Brun, P.; Brunetti, L.; Bruno, P.; Bucciantini, N.;
Buanes, T.; Buckley, J.; Bühler, R.; Bugaev, V.; Bulgarelli, A.;
Bulik, T.; Busetto, G.; Buson, S.; Byrum, K.; Cailles, M.; Cameron,
R.; Camprecios, J.; Canestrari, R.; Cantu, S.; Capalbi, M.; Caraveo,
P.; Carmona, E.; Carosi, A.; Carosi, R.; Carr, J.; Carter, J.;
Carton, P. -H.; Caruso, R.; Casanova, S.; Cascone, E.; Casiraghi, M.;
Castellina, A.; Catalano, O.; Cavazzani, S.; Cazaux, S.; Cerchiara,
P.; Cerruti, M.; Chabanne, E.; Chadwick, P.; Champion, C.; Chaves,
R.; Cheimets, P.; Chen, A.; Chiang, J.; Chiappetti, L.; Chikawa, M.;
Chitnis, V. R.; Chollet, F.; Christof, A.; Chudoba, J.; Cieślar, M.;
Cillis, A.; Cilmo, M.; Codino, A.; Cohen-Tanugi, J.; Colafrancesco,
S.; Colin, P.; Colome, J.; Colonges, S.; Compin, M.; Conconi, P.;
Conforti, V.; Connaughton, V.; Conrad, J.; Contreras, J. L.; Coppi,
P.; Coridian, J.; Corona, P.; Corti, D.; Cortina, J.; Cossio, L.;
Costa, A.; Costantini, H.; Cotter, G.; Courty, B.; Couturier, S.;
Covino, S.; Crimi, G.; Criswell, S. J.; Croston, J.; Cusumano, G.;
Dafonseca, M.; Dale, O.; Daniel, M.; Darling, J.; Davids, I.; Dazzi,
F.; de Angelis, A.; De Caprio, V.; De Frondat, F.; de Gouveia Dal Pino,
E. M.; de la Calle, I.; De La Vega, G. A.; de los Reyes Lopez, R.;
de Lotto, B.; De Luca, A.; de Naurois, M.; de Oliveira, Y.; de Oña
Wilhelmi, E.; de Palma, F.; de Souza, V.; Decerprit, G.; Decock, G.;
Deil, C.; Delagnes, E.; Deleglise, G.; Delgado, C.; della Volpe, D.;
Demange, P.; Depaola, G.; Dettlaff, A.; Di Girolamo, T.; Di Giulio,
C.; Di Paola, A.; Di Pierro, F.; di Sciascio, G.; Díaz, C.; Dick, J.;
Dickherber, R.; Dickinson, H.; Diez-Blanco, V.; Digel, S.; Dimitrov,
D.; Disset, G.; Djannati-Ataï, A.; Doert, M.; Dohmke, M.; Domainko,
W.; Dominis Prester, D.; Donat, A.; Dorner, D.; Doro, M.; Dournaux,
J. -L.; Drake, G.; Dravins, D.; Drury, L.; Dubois, F.; Dubois, R.;
Dubus, G.; Dufour, C.; Dumas, D.; Dumm, J.; Durand, D.; Dwarkadas, V.;
Dyks, J.; Dyrda, M.; Ebr, J.; Edy, E.; Egberts, K.; Eger, P.; Einecke,
S.; Eleftheriadis, C.; Elles, S.; Emmanoulopoulos, D.; Engelhaupt,
D.; Enomoto, R.; Ernenwein, J. -P.; Errando, M.; Etchegoyen, A.;
Evans, P. A.; Falcone, A.; Faltenbacher, A.; Fantinel, D.; Farakos,
K.; Farnier, C.; Farrell, E.; Fasola, G.; Favill, B. W.; Fede,
E.; Federici, S.; Fegan, S.; Feinstein, F.; Ferenc, D.; Ferrando,
P.; Fesquet, M.; Fetfatzis, P.; Fiasson, A.; Fillin-Martino, E.;
Fink, D.; Finley, C.; Finley, J. P.; Fiorini, M.; Firpo Curcoll,
R.; Flandrini, E.; Fleischhack, H.; Flores, H.; Florin, D.; Focke,
W.; Föhr, C.; Fokitis, E.; Font, L.; Fontaine, G.; Fornasa, M.;
Förster, A.; Fortson, L.; Fouque, N.; Franckowiak, A.; Franco, F. J.;
Frankowski, A.; Fransson, C.; Fraser, G. W.; Frei, R.; Fresnillo, L.;
Fruck, C.; Fugazza, D.; Fujita, Y.; Fukazawa, Y.; Fukui, Y.; Funk,
S.; Gäbele, W.; Gabici, S.; Gabriele, R.; Gadola, A.; Galante, N.;
Gall, D.; Gallant, Y.; Gámez-García, J.; Garczarczyk, M.; García,
B.; Garcia López, R.; Gardiol, D.; Gargano, F.; Garrido, D.; Garrido,
L.; Gascon, D.; Gaug, M.; Gaweda, J.; Gebremedhin, L.; Geffroy, N.;
Gerard, L.; Ghedina, A.; Ghigo, M.; Ghislain, P.; Giannakaki, E.;
Gianotti, F.; Giarrusso, S.; Giavitto, G.; Giebels, B.; Giglietto,
N.; Gika, V.; Giomi, M.; Giommi, P.; Giordano, F.; Girard, N.; Giro,
E.; Giuliani, A.; Glanzman, T.; Glicenstein, J. -F.; Godinovic, N.;
Golev, V.; Gomez Berisso, M.; Gómez-Ortega, J.; Gonzalez, M. M.;
González, A.; González, F.; González Muñoz, A.; Gothe, K. S.;
Grabarczyk, T.; Gougerot, M.; Graciani, R.; Grandi, P.; Grañena,
F.; Granot, J.; Grasseau, G.; Gredig, R.; Green, A.; Greenshaw, T.;
Grégoire, T.; Grillo, A.; Grimm, O.; Grondin, M. -H.; Grube, J.;
Grudzinska, M.; Gruev, V.; Grünewald, S.; Grygorczuk, J.; Guarino,
V.; Gunji, S.; Gyuk, G.; Hadasch, D.; Hagedorn, A.; Hagiwara, R.;
Hahn, J.; Hakansson, N.; Hallgren, A.; Hamer Heras, N.; Hara, S.;
Hardcastle, M. J.; Harezlak, D.; Harris, J.; Hassan, T.; Hatanaka,
K.; Haubold, T.; Haupt, A.; Hayakawa, T.; Hayashida, M.; Heller, R.;
Henault, F.; Henri, G.; Hermann, G.; Hermel, R.; Herrero, A.; Hervet,
O.; Hidaka, N.; Hinton, J. A.; Hirotani, K.; Hoffmann, D.; Hofmann,
W.; Hofverberg, P.; Holder, J.; Hörandel, J. R.; Horns, D.; Horville,
D.; Houles, J.; Hrabovsky, M.; Hrupec, D.; Huan, H.; Huber, B.; Huet,
J. -M.; Hughes, G.; Humensky, T. B.; Huovelin, J.; Huppert, J. -F.;
Ibarra, A.; Ikawa, D.; Illa, J. M.; Impiombato, D.; Incorvaia, S.;
Inoue, S.; Inoue, Y.; Iocco, F.; Ioka, K.; Israel, G. L.; Jablonski,
C.; Jacholkowska, A.; Jacquemier, J.; Jamrozy, M.; Janiak, M.; Jean,
P.; Jeanney, C.; Jimenez, J. J.; Jogler, T.; Johnson, C.; Johnson,
T.; Journet, L.; Juffroy, C.; Jung, I.; Kaaret, P.; Kabuki, S.;
Kagaya, M.; Kakuwa, J.; Kalkuhl, C.; Kankanyan, R.; Karastergiou,
A.; Kärcher, K.; Karczewski, M.; Karkar, S.; Kasperek, J.; Kastana,
D.; Katagiri, H.; Kataoka, J.; Katarzyński, K.; Katz, U.; Kawanaka,
N.; Kazanas, D.; Kelley-Hoskins, N.; Kellner-Leidel, B.; Kelly, H.;
Kendziorra, E.; Khélifi, B.; Kieda, D. B.; Kifune, T.; Kihm, T.;
Kishimoto, T.; Kitamoto, K.; Kluźniak, W.; Knapic, C.; Knapp, J.;
Knödlseder, J.; Köck, F.; Kocot, J.; Kodani, K.; Köhne, J. -H.;
Kohri, K.; Kokkotas, K.; Kolitzus, D.; Komin, N.; Kominis, I.; Konno,
Y.; Köppel, H.; Korohoda, P.; Kosack, K.; Koss, G.; Kossakowski,
R.; Koul, R.; Kowal, G.; Koyama, S.; Kozioł, J.; Krähenbühl, T.;
Krause, J.; Krawzcynski, H.; Krennrich, F.; Krepps, A.; Kretzschmann,
A.; Krobot, R.; Krueger, P.; Kubo, H.; Kudryavtsev, V. A.; Kushida,
J.; Kuznetsov, A.; La Barbera, A.; La Palombara, N.; La Parola, V.;
La Rosa, G.; Lacombe, K.; Lamanna, G.; Lande, J.; Languignon, D.;
Lapington, J. S.; Laporte, P.; Laurent, B.; Lavalley, C.; Le Flour,
T.; Le Padellec, A.; Lee, S. -H.; Lee, W. H.; Lefèvre, J. -P.; Leich,
H.; Leigui de Oliveira, M. A.; Lelas, D.; Lenain, J. -P.; Leoni,
R.; Leopold, D. J.; Lerch, T.; Lessio, L.; Leto, G.; Lieunard, B.;
Lieunard, S.; Lindemann, R.; Lindfors, E.; Liolios, A.; Lipniacka,
A.; Lockart, H.; Lohse, T.; Lombardi, S.; Longo, F.; Lopatin, A.;
Lopez, M.; López-Coto, R.; López-Oramas, A.; Lorca, A.; Lorenz,
E.; Louis, F.; Lubinski, P.; Lucarelli, F.; Lüdecke, H.; Ludwin, J.;
Luque-Escamilla, P. L.; Lustermann, W.; Luz, O.; Lyard, E.; Maccarone,
M. C.; Maccarone, T. J.; Madejski, G. M.; Madhavan, A.; Mahabir, M.;
Maier, G.; Majumdar, P.; Malaguti, G.; Malaspina, G.; Maltezos, S.;
Manalaysay, A.; Mancilla, A.; Mandat, D.; Maneva, G.; Mangano, A.;
Manigot, P.; Mannheim, K.; Manthos, I.; Maragos, N.; Marcowith, A.;
Mariotti, M.; Marisaldi, M.; Markoff, S.; Marszałek, A.; Martens,
C.; Martí, J.; Martin, J. -M.; Martin, P.; Martínez, G.; Martínez,
F.; Martínez, M.; Massaro, F.; Masserot, A.; Mastichiadis, A.;
Mathieu, A.; Matsumoto, H.; Mattana, F.; Mattiazzo, S.; Maurer, A.;
Maurin, G.; Maxfield, S.; Maya, J.; Mazin, D.; Mc Comb, L.; McCann,
A.; McCubbin, N.; McHardy, I.; McKay, R.; Meagher, K.; Medina, C.;
Melioli, C.; Melkumyan, D.; Melo, D.; Mereghetti, S.; Mertsch, P.;
Meucci, M.; Meyer, M.; Michałowski, J.; Micolon, P.; Mihailidis,
A.; Mineo, T.; Minuti, M.; Mirabal, N.; Mirabel, F.; Miranda, J. M.;
Mirzoyan, R.; Mistò, A.; Mizuno, T.; Moal, B.; Moderski, R.; Mognet,
I.; Molinari, E.; Molinaro, M.; Montaruli, T.; Monte, C.; Monteiro, I.;
Moore, P.; Moralejo Olaizola, A.; Mordalska, M.; Morello, C.; Mori,
K.; Morlino, G.; Morselli, A.; Mottez, F.; Moudden, Y.; Moulin, E.;
Mrusek, I.; Mukherjee, R.; Munar-Adrover, P.; Muraishi, H.; Murase, K.;
StJ. Murphy, A.; Nagataki, S.; Naito, T.; Nakajima, D.; Nakamori, T.;
Nakayama, K.; Naumann, C.; Naumann, D.; Naumann-Godo, M.; Nayman, P.;
Nedbal, D.; Neise, D.; Nellen, L.; Neronov, A.; Neustroev, V.; Neyroud,
N.; Nicastro, L.; Nicolau-Kukliński, J.; Niedźwiecki, A.; Niemiec,
J.; Nieto, D.; Nikolaidis, A.; Nishijima, K.; Nishikawa, K. -I.;
Noda, K.; Nolan, S.; Northrop, R.; Nosek, D.; Nowak, N.; Nozato, A.;
Oakes, L.; O'Brien, P. T.; Ohira, Y.; Ohishi, M.; Ohm, S.; Ohoka, H.;
Okuda, T.; Okumura, A.; Olive, J. -F.; Ong, R. A.; Orito, R.; Orr, M.;
Osborne, J. P.; Ostrowski, M.; Otero, L. A.; Otte, N.; Ovcharov, E.;
Oya, I.; Ozieblo, A.; Padilla, L.; Pagano, I.; Paiano, S.; Paillot, D.;
Paizis, A.; Palanque, S.; Palatka, M.; Pallota, J.; Palatiello, M.;
Panagiotidis, K.; Panazol, J. -L.; Paneque, D.; Panter, M.; Panzera,
M. R.; Paoletti, R.; Papayannis, A.; Papyan, G.; Paredes, J. M.;
Pareschi, G.; Parraud, J. -M.; Parsons, D.; Pauletta, G.; Paz Arribas,
M.; Pech, M.; Pedaletti, G.; Pelassa, V.; Pelat, D.; Perez, M. d. C.;
Persic, M.; Petrucci, P. -O.; Peyaud, B.; Pichel, A.; Pieloth, D.;
Pierre, E.; Pita, S.; Pivato, G.; Pizzolato, F.; Platino, M.; Platos,
Ł.; Platzer, R.; Podkladkin, S.; Pogosyan, L.; Pohl, M.; Pojmanski,
G.; Ponz, J. D.; Potter, W.; Poutanen, J.; Prandini, E.; Prast,
J.; Preece, R.; Profeti, F.; Prokoph, H.; Prouza, M.; Proyetti, M.;
Puerto-Giménez, I.; Pühlhofer, G.; Puljak, I.; Punch, M.; Pyzioł,
R.; Quel, E. J.; Quesada, J.; Quinn, J.; Quirrenbach, A.; Racero, E.;
Rainò, S.; Rajda, P. J.; Rameez, M.; Ramon, P.; Rando, R.; Rannot,
R. C.; Rataj, M.; Raue, M.; Ravignani, D.; Reardon, P.; Reimann,
O.; Reimer, A.; Reimer, O.; Reitberger, K.; Renaud, M.; Renner,
S.; Reville, B.; Rhode, W.; Ribó, M.; Ribordy, M.; Richards, G.;
Richer, M. G.; Rico, J.; Ridky, J.; Rieger, F.; Ringegni, P.; Ripken,
J.; Ristori, P. R.; Rivière, A.; Rivoire, S.; Rob, L.; Rodeghiero,
G.; Roeser, U.; Rohlfs, R.; Rojas, G.; Romano, P.; Romaszkan, W.;
Romero, G. E.; Rosen, S. R.; Rosier Lees, S.; Ross, D.; Rouaix, G.;
Rousselle, J.; Rousselle, S.; Rovero, A. C.; Roy, F.; Royer, S.;
Rudak, B.; Rulten, C.; Rupiński, M.; Russo, F.; Ryde, F.; Saavedra,
O.; Sacco, B.; Saemann, E. O.; Saggion, A.; Sahakian, V.; Saito, K.;
Saito, T.; Saito, Y.; Sakaki, N.; Sakonaka, R.; Salini, A.; Sanchez,
F.; Sanchez-Conde, M.; Sandoval, A.; Sandaker, H.; Sant'Ambrogio, E.;
Santangelo, A.; Santos, E. M.; Sanuy, A.; Sapozhnikov, L.; Sarkar,
S.; Sartore, N.; Sasaki, H.; Satalecka, K.; Sawada, M.; Scalzotto, V.;
Scapin, V.; Scarcioffolo, M.; Schafer, J.; Schanz, T.; Schlenstedt,
S.; Schlickeiser, R.; Schmidt, T.; Schmoll, J.; Schovanek, P.;
Schroedter, M.; Schubert, A.; Schultz, C.; Schultze, J.; Schulz,
A.; Schure, K.; Schussler, F.; Schwab, T.; Schwanke, U.; Schwarz,
J.; Schwarzburg, S.; Schweizer, T.; Schwemmer, S.; Schwendicke, U.;
Schwerdt, C.; Segreto, A.; Seiradakis, J. -H.; Sembroski, G. H.;
Servillat, M.; Seweryn, K.; Sharma, M.; Shayduk, M.; Shellard,
R. C.; Shi, J.; Shibata, T.; Shibuya, A.; Shore, S.; Shum, E.;
Sideras-Haddad, E.; Sidoli, L.; Sidz, M.; Sieiro, J.; Sikora, M.;
Silk, J.; Sillanpää, A.; Singh, B. B.; Sironi, G.; Sitarek, J.;
Skole, C.; Smareglia, R.; Smith, A.; Smith, D.; Smith, J.; Smith,
N.; Sobczyńska, D.; Sol, H.; Sottile, G.; Sowiński, M.; Spanier,
F.; Spiga, D.; Spyrou, S.; Stamatescu, V.; Stamerra, A.; Starling,
R. L. C.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Steiner, S.;
Stella, C.; Stergioulas, N.; Sternberger, R.; Sterzel, M.; Stinzing,
F.; Stodulski, M.; Stolarczyk, Th.; Straumann, U.; Strazzeri, E.;
Stringhetti, L.; Suarez, A.; Suchenek, M.; Sugawara, R.; Sulanke,
K. -H.; Sun, S.; Supanitsky, A. D.; Suric, T.; Sutcliffe, P.; Sykes,
J. M.; Szanecki, M.; Szepieniec, T.; Szostek, A.; Tagliaferri, G.;
Tajima, H.; Takahashi, H.; Takahashi, K.; Takalo, L.; Takami, H.;
Talbot, G.; Tammi, J.; Tanaka, M.; Tanaka, S.; Tasan, J.; Tavani,
M.; Tavernet, J. -P.; Tejedor, L. A.; Telezhinsky, I.; Temnikov, P.;
Tenzer, C.; Terada, Y.; Terrier, R.; Teshima, M.; Testa, V.; Tezier,
D.; Thayer, J.; Thuermann, D.; Tibaldo, L.; Tibaldo, L.; Tibolla,
O.; Tiengo, A.; Timpanaro, M. C.; Tluczykont, M.; Todero Peixoto,
C. J.; Tokanai, F.; Tokarz, M.; Toma, K.; Tonachini, A.; Torii, K.;
Tornikoski, M.; Torres, D. F.; Torres, M.; Toscano, S.; Toso, G.;
Tosti, G.; Totani, T.; Toussenel, F.; Tovmassian, G.; Travnicek, P.;
Treves, A.; Trifoglio, M.; Troyano, I.; Tsinganos, K.; Ueno, H.; Umana,
G.; Umehara, K.; Upadhya, S. S.; Usher, T.; Uslenghi, M.; Vagnetti, F.;
Valdes-Galicia, J. F.; Vallania, P.; Vallejo, G.; van Driel, W.; van
Eldik, C.; Vandenbrouke, J.; Vanderwalt, J.; Vankov, H.; Vasileiadis,
G.; Vassiliev, V.; Veberic, D.; Vegas, I.; Vercellone, S.; Vergani,
S.; Verzi, V.; Vettolani, G. P.; Veyssière, C.; Vialle, J. P.;
Viana, A.; Videla, M.; Vigorito, C.; Vincent, P.; Vincent, S.; Vink,
J.; Vlahakis, N.; Vlahos, L.; Vogler, P.; Voisin, V.; Vollhardt, A.;
von Gunten, H. -P.; Vorobiov, S.; Vuerli, C.; Waegebaert, V.; Wagner,
R.; Wagner, R. G.; Wagner, S.; Wakely, S. P.; Walter, R.; Walther,
T.; Warda, K.; Warwick, R. S.; Wawer, P.; Wawrzaszek, R.; Webb, N.;
Wegner, P.; Weinstein, A.; Weitzel, Q.; Welsing, R.; Werner, M.;
Wetteskind, H.; White, R. J.; Wierzcholska, A.; Wiesand, S.; Wilhelm,
A.; Wilkinson, M. I.; Williams, D. A.; Willingale, R.; Winde, M.;
Winiarski, K.; Wischnewski, R.; Wiśniewski, Ł.; Wojcik, P.; Wood,
M.; Wörnlein, A.; Xiong, Q.; Yadav, K. K.; Yamamoto, H.; Yamamoto,
T.; Yamazaki, R.; Yanagita, S.; Yebras, J. M.; Yelos, D.; Yoshida,
A.; Yoshida, T.; Yoshikoshi, T.; Yu, P.; Zabalza, V.; Zacharias, M.;
Zajczyk, A.; Zampieri, L.; Zanin, R.; Zdziarski, A.; Zech, A.; Zhao,
A.; Zhou, X.; Zietara, K.; Ziolkowski, J.; Ziółkowski, P.; Zitelli,
V.; Zurbach, C.; Zychowski, P.
2013arXiv1307.2232C Altcode:
Compilation of CTA contributions to the proceedings of the 33rd
International Cosmic Ray Conference (ICRC2013), which took place in
2-9 July, 2013, in Rio de Janeiro, Brazil
---------------------------------------------------------
Title: Dynamic data-driven integrated flare model based on
self-organized criticality
Authors: Dimitropoulou, M.; Isliker, H.; Vlahos, L.; Georgoulis, M. K.
2013A&A...553A..65D Altcode:
Context. We interpret solar flares as events originating in active
regions that have reached the self-organized critical state. We describe
them with a dynamic integrated flare model whose initial conditions
and driving mechanism are derived from observations. <BR /> Aims: We
investigate whether well-known scaling laws observed in the distribution
functions of characteristic flare parameters are reproduced after
the self-organized critical state has been reached. <BR /> Methods:
To investigate whether the distribution functions of total energy,
peak energy, and event duration follow the expected scaling laws,
we first applied the previously reported static cellular automaton
model to a time series of seven solar vector magnetograms of the NOAA
active region 8210 recorded by the Imaging Vector Magnetograph on May
1 1998 between 18:59 UT and 23:16 UT until the self-organized critical
state was reached. We then evolved the magnetic field between these
processed snapshots through spline interpolation, mimicking a natural
driver in our dynamic model. We identified magnetic discontinuities
that exceeded a threshold in the Laplacian of the magnetic field after
each interpolation step. These discontinuities were relaxed in local
diffusion events, implemented in the form of cellular automaton
evolution rules. Subsequent interpolation and relaxation steps
covered all transitions until the end of the processed magnetograms'
sequence. We additionally advanced each magnetic configuration that
has reached the self-organized critical state (SOC configuration)
by the static model until 50 more flares were triggered, applied
the dynamic model again to the new sequence, and repeated the same
process sufficiently often to generate adequate statistics. Physical
requirements, such as the divergence-free condition for the magnetic
field, were approximately imposed. <BR /> Results: We obtain robust
power laws in the distribution functions of the modeled flaring events
with scaling indices that agree well with observations. Peak and total
flare energy obey single power laws with indices -1.65 ± 0.11 and
-1.47 ± 0.13, while the flare duration is best fitted with a double
power law (-2.15 ± 0.15 and -3.60 ± 0.09 for the flatter and steeper
parts, respectively). <BR /> Conclusions: We conclude that well-known
statistical properties of flares are reproduced after active regions
reach the state of self-organized criticality. A significant enhancement
of our refined cellular automaton model is that it initiates and further
drives the simulation from observed evolving vector magnetograms, thus
facilitating energy calculation in physical units, while a separation
between MHD and kinetic timescales is possible by assigning distinct
MHD timestamps to each interpolation step.
---------------------------------------------------------
Title: Introducing the CTA concept
Authors: Acharya, B. S.; Actis, M.; Aghajani, T.; Agnetta, G.;
Aguilar, J.; Aharonian, F.; Ajello, M.; Akhperjanian, A.; Alcubierre,
M.; Aleksić, J.; Alfaro, R.; Aliu, E.; Allafort, A. J.; Allan, D.;
Allekotte, I.; Amato, E.; Anderson, J.; Angüner, E. O.; Antonelli,
L. A.; Antoranz, P.; Aravantinos, A.; Arlen, T.; Armstrong, T.;
Arnaldi, H.; Arrabito, L.; Asano, K.; Ashton, T.; Asorey, H. G.; Awane,
Y.; Baba, H.; Babic, A.; Baby, N.; Bähr, J.; Bais, A.; Baixeras, C.;
Bajtlik, S.; Balbo, M.; Balis, D.; Balkowski, C.; Bamba, A.; Bandiera,
R.; Barber, A.; Barbier, C.; Barceló, M.; Barnacka, A.; Barnstedt, J.;
Barres de Almeida, U.; Barrio, J. A.; Basili, A.; Basso, S.; Bastieri,
D.; Bauer, C.; Baushev, A.; Becerra, J.; Becherini, Y.; Bechtol, K. C.;
Becker Tjus, J.; Beckmann, V.; Bednarek, W.; Behera, B.; Belluso,
M.; Benbow, W.; Berdugo, J.; Berger, K.; Bernard, F.; Bernardino, T.;
Bernlöhr, K.; Bhat, N.; Bhattacharyya, S.; Bigongiari, C.; Biland,
A.; Billotta, S.; Bird, T.; Birsin, E.; Bissaldi, E.; Biteau, J.;
Bitossi, M.; Blake, S.; Blanch Bigas, O.; Blasi, P.; Bobkov, A.;
Boccone, V.; Boettcher, M.; Bogacz, L.; Bogart, J.; Bogdan, M.;
Boisson, C.; Boix Gargallo, J.; Bolmont, J.; Bonanno, G.; Bonardi,
A.; Bonev, T.; Bonifacio, P.; Bonnoli, G.; Bordas, P.; Borgland,
A.; Borkowski, J.; Bose, R.; Botner, O.; Bottani, A.; Bouchet, L.;
Bourgeat, M.; Boutonnet, C.; Bouvier, A.; Brau-Nogué, S.; Braun, I.;
Bretz, T.; Briggs, M.; Bringmann, T.; Brook, P.; Brun, P.; Brunetti,
L.; Buanes, T.; Buckley, J.; Buehler, R.; Bugaev, V.; Bulgarelli, A.;
Bulik, T.; Busetto, G.; Buson, S.; Byrum, K.; Cailles, M.; Cameron,
R.; Camprecios, J.; Canestrari, R.; Cantu, S.; Capalbi, M.; Caraveo,
P.; Carmona, E.; Carosi, A.; Carr, J.; Carton, P. -H.; Casanova,
S.; Casiraghi, M.; Catalano, O.; Cavazzani, S.; Cazaux, S.; Cerruti,
M.; Chabanne, E.; Chadwick, P.; Champion, C.; Chen, A.; Chiang, J.;
Chiappetti, L.; Chikawa, M.; Chitnis, V. R.; Chollet, F.; Chudoba, J.;
Cieślar, M.; Cillis, A.; Cohen-Tanugi, J.; Colafrancesco, S.; Colin,
P.; Colome, J.; Colonges, S.; Compin, M.; Conconi, P.; Conforti, V.;
Connaughton, V.; Conrad, J.; Contreras, J. L.; Coppi, P.; Corona, P.;
Corti, D.; Cortina, J.; Cossio, L.; Costantini, H.; Cotter, G.; Courty,
B.; Couturier, S.; Covino, S.; Crimi, G.; Criswell, S. J.; Croston,
J.; Cusumano, G.; Dafonseca, M.; Dale, O.; Daniel, M.; Darling, J.;
Davids, I.; Dazzi, F.; De Angelis, A.; De Caprio, V.; De Frondat,
F.; de Gouveia Dal Pino, E. M.; de la Calle, I.; De La Vega, G. A.;
de los Reyes Lopez, R.; De Lotto, B.; De Luca, A.; de Mello Neto,
J. R. T.; de Naurois, M.; de Oliveira, Y.; de Oña Wilhelmi, E.;
de Souza, V.; Decerprit, G.; Decock, G.; Deil, C.; Delagnes, E.;
Deleglise, G.; Delgado, C.; Della Volpe, D.; Demange, P.; Depaola,
G.; Dettlaff, A.; Di Paola, A.; Di Pierro, F.; Díaz, C.; Dick, J.;
Dickherber, R.; Dickinson, H.; Diez-Blanco, V.; Digel, S.; Dimitrov,
D.; Disset, G.; Djannati-Ataï, A.; Doert, M.; Dohmke, M.; Domainko,
W.; Dominis Prester, D.; Donat, A.; Dorner, D.; Doro, M.; Dournaux,
J. -L.; Drake, G.; Dravins, D.; Drury, L.; Dubois, F.; Dubois, R.;
Dubus, G.; Dufour, C.; Dumas, D.; Dumm, J.; Durand, D.; Dyks, J.;
Dyrda, M.; Ebr, J.; Edy, E.; Egberts, K.; Eger, P.; Einecke, S.;
Eleftheriadis, C.; Elles, S.; Emmanoulopoulos, D.; Engelhaupt, D.;
Enomoto, R.; Ernenwein, J. -P.; Errando, M.; Etchegoyen, A.; Evans,
P.; Falcone, A.; Fantinel, D.; Farakos, K.; Farnier, C.; Fasola,
G.; Favill, B.; Fede, E.; Federici, S.; Fegan, S.; Feinstein, F.;
Ferenc, D.; Ferrando, P.; Fesquet, M.; Fiasson, A.; Fillin-Martino,
E.; Fink, D.; Finley, C.; Finley, J. P.; Fiorini, M.; Firpo Curcoll,
R.; Flores, H.; Florin, D.; Focke, W.; Föhr, C.; Fokitis, E.; Font,
L.; Fontaine, G.; Fornasa, M.; Förster, A.; Fortson, L.; Fouque,
N.; Franckowiak, A.; Fransson, C.; Fraser, G.; Frei, R.; Albuquerque,
I. F. M.; Fresnillo, L.; Fruck, C.; Fujita, Y.; Fukazawa, Y.; Fukui,
Y.; Funk, S.; Gäbele, W.; Gabici, S.; Gabriele, R.; Gadola, A.;
Galante, N.; Gall, D.; Gallant, Y.; Gámez-García, J.; García, B.;
Garcia López, R.; Gardiol, D.; Garrido, D.; Garrido, L.; Gascon,
D.; Gaug, M.; Gaweda, J.; Gebremedhin, L.; Geffroy, N.; Gerard, L.;
Ghedina, A.; Ghigo, M.; Giannakaki, E.; Gianotti, F.; Giarrusso, S.;
Giavitto, G.; Giebels, B.; Gika, V.; Giommi, P.; Girard, N.; Giro,
E.; Giuliani, A.; Glanzman, T.; Glicenstein, J. -F.; Godinovic, N.;
Golev, V.; Gomez Berisso, M.; Gómez-Ortega, J.; Gonzalez, M. M.;
González, A.; González, F.; González Muñoz, A.; Gothe, K. S.;
Gougerot, M.; Graciani, R.; Grandi, P.; Grañena, F.; Granot, J.;
Grasseau, G.; Gredig, R.; Green, A.; Greenshaw, T.; Grégoire,
T.; Grimm, O.; Grube, J.; Grudzinska, M.; Gruev, V.; Grünewald,
S.; Grygorczuk, J.; Guarino, V.; Gunji, S.; Gyuk, G.; Hadasch, D.;
Hagiwara, R.; Hahn, J.; Hakansson, N.; Hallgren, A.; Hamer Heras,
N.; Hara, S.; Hardcastle, M. J.; Harris, J.; Hassan, T.; Hatanaka,
K.; Haubold, T.; Haupt, A.; Hayakawa, T.; Hayashida, M.; Heller, R.;
Henault, F.; Henri, G.; Hermann, G.; Hermel, R.; Herrero, A.; Hidaka,
N.; Hinton, J.; Hoffmann, D.; Hofmann, W.; Hofverberg, P.; Holder, J.;
Horns, D.; Horville, D.; Houles, J.; Hrabovsky, M.; Hrupec, D.; Huan,
H.; Huber, B.; Huet, J. -M.; Hughes, G.; Humensky, T. B.; Huovelin,
J.; Ibarra, A.; Illa, J. M.; Impiombato, D.; Incorvaia, S.; Inoue,
S.; Inoue, Y.; Ioka, K.; Ismailova, E.; Jablonski, C.; Jacholkowska,
A.; Jamrozy, M.; Janiak, M.; Jean, P.; Jeanney, C.; Jimenez, J. J.;
Jogler, T.; Johnson, T.; Journet, L.; Juffroy, C.; Jung, I.; Kaaret,
P.; Kabuki, S.; Kagaya, M.; Kakuwa, J.; Kalkuhl, C.; Kankanyan, R.;
Karastergiou, A.; Kärcher, K.; Karczewski, M.; Karkar, S.; Kasperek,
J.; Kastana, D.; Katagiri, H.; Kataoka, J.; Katarzyński, K.; Katz,
U.; Kawanaka, N.; Kellner-Leidel, B.; Kelly, H.; Kendziorra, E.;
Khélifi, B.; Kieda, D. B.; Kifune, T.; Kihm, T.; Kishimoto, T.;
Kitamoto, K.; Kluźniak, W.; Knapic, C.; Knapp, J.; Knödlseder, J.;
Köck, F.; Kocot, J.; Kodani, K.; Köhne, J. -H.; Kohri, K.; Kokkotas,
K.; Kolitzus, D.; Komin, N.; Kominis, I.; Konno, Y.; Köppel, H.;
Korohoda, P.; Kosack, K.; Koss, G.; Kossakowski, R.; Kostka, P.;
Koul, R.; Kowal, G.; Koyama, S.; Kozioł, J.; Krähenbühl, T.;
Krause, J.; Krawzcynski, H.; Krennrich, F.; Krepps, A.; Kretzschmann,
A.; Krobot, R.; Krueger, P.; Kubo, H.; Kudryavtsev, V. A.; Kushida,
J.; Kuznetsov, A.; La Barbera, A.; La Palombara, N.; La Parola, V.;
La Rosa, G.; Lacombe, K.; Lamanna, G.; Lande, J.; Languignon, D.;
Lapington, J.; Laporte, P.; Lavalley, C.; Le Flour, T.; Le Padellec,
A.; Lee, S. -H.; Lee, W. H.; Leigui de Oliveira, M. A.; Lelas, D.;
Lenain, J. -P.; Leopold, D. J.; Lerch, T.; Lessio, L.; Lieunard, B.;
Lindfors, E.; Liolios, A.; Lipniacka, A.; Lockart, H.; Lohse, T.;
Lombardi, S.; Lopatin, A.; Lopez, M.; López-Coto, R.; López-Oramas,
A.; Lorca, A.; Lorenz, E.; Lubinski, P.; Lucarelli, F.; Lüdecke, H.;
Ludwin, J.; Luque-Escamilla, P. L.; Lustermann, W.; Luz, O.; Lyard,
E.; Maccarone, M. C.; Maccarone, T. J.; Madejski, G. M.; Madhavan,
A.; Mahabir, M.; Maier, G.; Majumdar, P.; Malaguti, G.; Maltezos, S.;
Manalaysay, A.; Mancilla, A.; Mandat, D.; Maneva, G.; Mangano, A.;
Manigot, P.; Mannheim, K.; Manthos, I.; Maragos, N.; Marcowith, A.;
Mariotti, M.; Marisaldi, M.; Markoff, S.; Marszałek, A.; Martens, C.;
Martí, J.; Martin, J. -M.; Martin, P.; Martínez, G.; Martínez, F.;
Martínez, M.; Masserot, A.; Mastichiadis, A.; Mathieu, A.; Matsumoto,
H.; Mattana, F.; Mattiazzo, S.; Maurin, G.; Maxfield, S.; Maya, J.;
Mazin, D.; Mc Comb, L.; McCubbin, N.; McHardy, I.; McKay, R.; Medina,
C.; Melioli, C.; Melkumyan, D.; Mereghetti, S.; Mertsch, P.; Meucci,
M.; Michałowski, J.; Micolon, P.; Mihailidis, A.; Mineo, T.; Minuti,
M.; Mirabal, N.; Mirabel, F.; Miranda, J. M.; Mirzoyan, R.; Mizuno,
T.; Moal, B.; Moderski, R.; Mognet, I.; Molinari, E.; Molinaro,
M.; Montaruli, T.; Monteiro, I.; Moore, P.; Moralejo Olaizola,
A.; Mordalska, M.; Morello, C.; Mori, K.; Mottez, F.; Moudden, Y.;
Moulin, E.; Mrusek, I.; Mukherjee, R.; Munar-Adrover, P.; Muraishi,
H.; Murase, K.; Murphy, A.; Nagataki, S.; Naito, T.; Nakajima, D.;
Nakamori, T.; Nakayama, K.; Naumann, C.; Naumann, D.; Naumann-Godo,
M.; Nayman, P.; Nedbal, D.; Neise, D.; Nellen, L.; Neustroev, V.;
Neyroud, N.; Nicastro, L.; Nicolau-Kukliński, J.; Niedźwiecki, A.;
Niemiec, J.; Nieto, D.; Nikolaidis, A.; Nishijima, K.; Nolan, S.;
Northrop, R.; Nosek, D.; Nowak, N.; Nozato, A.; O'Brien, P.; Ohira,
Y.; Ohishi, M.; Ohm, S.; Ohoka, H.; Okuda, T.; Okumura, A.; Olive,
J. -F.; Ong, R. A.; Orito, R.; Orr, M.; Osborne, J.; Ostrowski, M.;
Otero, L. A.; Otte, N.; Ovcharov, E.; Oya, I.; Ozieblo, A.; Padilla,
L.; Paiano, S.; Paillot, D.; Paizis, A.; Palanque, S.; Palatka, M.;
Pallota, J.; Panagiotidis, K.; Panazol, J. -L.; Paneque, D.; Panter,
M.; Paoletti, R.; Papayannis, A.; Papyan, G.; Paredes, J. M.; Pareschi,
G.; Parks, G.; Parraud, J. -M.; Parsons, D.; Paz Arribas, M.; Pech,
M.; Pedaletti, G.; Pelassa, V.; Pelat, D.; Perez, M. d. C.; Persic,
M.; Petrucci, P. -O.; Peyaud, B.; Pichel, A.; Pita, S.; Pizzolato, F.;
Platos, Ł.; Platzer, R.; Pogosyan, L.; Pohl, M.; Pojmanski, G.; Ponz,
J. D.; Potter, W.; Poutanen, J.; Prandini, E.; Prast, J.; Preece, R.;
Profeti, F.; Prokoph, H.; Prouza, M.; Proyetti, M.; Puerto-Gimenez, I.;
Pühlhofer, G.; Puljak, I.; Punch, M.; Pyzioł, R.; Quel, E. J.; Quinn,
J.; Quirrenbach, A.; Racero, E.; Rajda, P. J.; Ramon, P.; Rando, R.;
Rannot, R. C.; Rataj, M.; Raue, M.; Reardon, P.; Reimann, O.; Reimer,
A.; Reimer, O.; Reitberger, K.; Renaud, M.; Renner, S.; Reville, B.;
Rhode, W.; Ribó, M.; Ribordy, M.; Richer, M. G.; Rico, J.; Ridky,
J.; Rieger, F.; Ringegni, P.; Ripken, J.; Ristori, P. R.; Riviére,
A.; Rivoire, S.; Rob, L.; Roeser, U.; Rohlfs, R.; Rojas, G.; Romano,
P.; Romaszkan, W.; Romero, G. E.; Rosen, S.; Rosier Lees, S.; Ross,
D.; Rouaix, G.; Rousselle, J.; Rousselle, S.; Rovero, A. C.; Roy,
F.; Royer, S.; Rudak, B.; Rulten, C.; Rupiński, M.; Russo, F.; Ryde,
F.; Sacco, B.; Saemann, E. O.; Saggion, A.; Sahakian, V.; Saito, K.;
Saito, T.; Saito, Y.; Sakaki, N.; Sakonaka, R.; Salini, A.; Sanchez,
F.; Sanchez-Conde, M.; Sandoval, A.; Sandaker, H.; Sant'Ambrogio,
E.; Santangelo, A.; Santos, E. M.; Sanuy, A.; Sapozhnikov, L.;
Sarkar, S.; Sartore, N.; Sasaki, H.; Satalecka, K.; Sawada, M.;
Scalzotto, V.; Scapin, V.; Scarcioffolo, M.; Schafer, J.; Schanz,
T.; Schlenstedt, S.; Schlickeiser, R.; Schmidt, T.; Schmoll, J.;
Schovanek, P.; Schroedter, M.; Schultz, C.; Schultze, J.; Schulz,
A.; Schure, K.; Schwab, T.; Schwanke, U.; Schwarz, J.; Schwarzburg,
S.; Schweizer, T.; Schwemmer, S.; Segreto, A.; Seiradakis, J. -H.;
Sembroski, G. H.; Seweryn, K.; Sharma, M.; Shayduk, M.; Shellard,
R. C.; Shi, J.; Shibata, T.; Shibuya, A.; Shum, E.; Sidoli, L.; Sidz,
M.; Sieiro, J.; Sikora, M.; Silk, J.; Sillanpää, A.; Singh, B. B.;
Sitarek, J.; Skole, C.; Smareglia, R.; Smith, A.; Smith, D.; Smith,
J.; Smith, N.; Sobczyńska, D.; Sol, H.; Sottile, G.; Sowiński, M.;
Spanier, F.; Spiga, D.; Spyrou, S.; Stamatescu, V.; Stamerra, A.;
Starling, R.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Steiner,
S.; Stergioulas, N.; Sternberger, R.; Sterzel, M.; Stinzing, F.;
Stodulski, M.; Straumann, U.; Strazzeri, E.; Stringhetti, L.;
Suarez, A.; Suchenek, M.; Sugawara, R.; Sulanke, K. -H.; Sun, S.;
Supanitsky, A. D.; Suric, T.; Sutcliffe, P.; Sykes, J.; Szanecki, M.;
Szepieniec, T.; Szostek, A.; Tagliaferri, G.; Tajima, H.; Takahashi,
H.; Takahashi, K.; Takalo, L.; Takami, H.; Talbot, G.; Tammi, J.;
Tanaka, M.; Tanaka, S.; Tasan, J.; Tavani, M.; Tavernet, J. -P.;
Tejedor, L. A.; Telezhinsky, I.; Temnikov, P.; Tenzer, C.; Terada,
Y.; Terrier, R.; Teshima, M.; Testa, V.; Tezier, D.; Thuermann, D.;
Tibaldo, L.; Tibolla, O.; Tiengo, A.; Tluczykont, M.; Todero Peixoto,
C. J.; Tokanai, F.; Tokarz, M.; Toma, K.; Torii, K.; Tornikoski,
M.; Torres, D. F.; Torres, M.; Tosti, G.; Totani, T.; Toussenel, F.;
Tovmassian, G.; Travnicek, P.; Trifoglio, M.; Troyano, I.; Tsinganos,
K.; Ueno, H.; Umehara, K.; Upadhya, S. S.; Usher, T.; Uslenghi, M.;
Valdes-Galicia, J. F.; Vallania, P.; Vallejo, G.; van Driel, W.; van
Eldik, C.; Vandenbrouke, J.; Vanderwalt, J.; Vankov, H.; Vasileiadis,
G.; Vassiliev, V.; Veberic, D.; Vegas, I.; Vercellone, S.; Vergani,
S.; Veyssiére, C.; Vialle, J. P.; Viana, A.; Videla, M.; Vincent, P.;
Vincent, S.; Vink, J.; Vlahakis, N.; Vlahos, L.; Vogler, P.; Vollhardt,
A.; von Gunten, H. -P.; Vorobiov, S.; Vuerli, C.; Waegebaert, V.;
Wagner, R.; Wagner, R. G.; Wagner, S.; Wakely, S. P.; Walter, R.;
Walther, T.; Warda, K.; Warwick, R.; Wawer, P.; Wawrzaszek, R.; Webb,
N.; Wegner, P.; Weinstein, A.; Weitzel, Q.; Welsing, R.; Werner, M.;
Wetteskind, H.; White, R.; Wierzcholska, A.; Wiesand, S.; Wilkinson,
M.; Williams, D. A.; Willingale, R.; Winiarski, K.; Wischnewski, R.;
Wiśniewski, Ł.; Wood, M.; Wörnlein, A.; Xiong, Q.; Yadav, K. K.;
Yamamoto, H.; Yamamoto, T.; Yamazaki, R.; Yanagita, S.; Yebras,
J. M.; Yelos, D.; Yoshida, A.; Yoshida, T.; Yoshikoshi, T.; Zabalza,
V.; Zacharias, M.; Zajczyk, A.; Zanin, R.; Zdziarski, A.; Zech, A.;
Zhao, A.; Zhou, X.; Ziętara, K.; Ziolkowski, J.; Ziółkowski, P.;
Zitelli, V.; Zurbach, C.; Żychowski, P.; CTA Consortium
2013APh....43....3A Altcode: 2013APh....43....3C
The Cherenkov Telescope Array (CTA) is a new observatory for very
high-energy (VHE) gamma rays. CTA has ambitions science goals, for which
it is necessary to achieve full-sky coverage, to improve the sensitivity
by about an order of magnitude, to span about four decades of energy,
from a few tens of GeV to above 100 TeV with enhanced angular and energy
resolutions over existing VHE gamma-ray observatories. An international
collaboration has formed with more than 1000 members from 27 countries
in Europe, Asia, Africa and North and South America. In 2010 the CTA
Consortium completed a Design Study and started a three-year Preparatory
Phase which leads to production readiness of CTA in 2014. In this paper
we introduce the science goals and the concept of CTA, and provide an
overview of the project.
---------------------------------------------------------
Title: Current Fragmentation and Particle Acceleration in Solar Flares
Authors: Cargill, P. J.; Vlahos, L.; Baumann, G.; Drake, J. F.;
Nordlund, Å.
2013pacp.book..223C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Turbulence, Magnetic Reconnection in Turbulent Fluids and
Energetic Particle Acceleration
Authors: Lazarian, A.; Vlahos, L.; Kowal, G.; Yan, H.; Beresnyak,
A.; de Gouveia Dal Pino, E. M.
2013pacp.book..557L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Current Fragmentation and Particle Acceleration in Solar Flares
Authors: Cargill, P. J.; Vlahos, L.; Baumann, G.; Drake, J. F.;
Nordlund, Å.
2012SSRv..173..223C Altcode: 2012SSRv..tmp...36C
Particle acceleration in solar flares remains an outstanding problem in
plasma physics and space science. While the observed particle energies
and timescales can perhaps be understood in terms of acceleration
at a simple current sheet or turbulence site, the vast number of
accelerated particles, and the fraction of flare energy in them, defies
any simple explanation. The nature of energy storage and dissipation
in the global coronal magnetic field is essential for understanding
flare acceleration. Scenarios where the coronal field is stressed by
complex photospheric motions lead to the formation of multiple current
sheets, rather than the single monolithic current sheet proposed by
some. The currents sheets in turn can fragment into multiple, smaller
dissipation sites. MHD, kinetic and cellular automata models are used to
demonstrate this feature. Particle acceleration in this environment thus
involves interaction with many distributed accelerators. A series of
examples demonstrate how acceleration works in such an environment. As
required, acceleration is fast, and relativistic energies are readily
attained. It is also shown that accelerated particles do indeed
interact with multiple acceleration sites. Test particle models also
demonstrate that a large number of particles can be accelerated, with a
significant fraction of the flare energy associated with them. However,
in the absence of feedback, and with limited numerical resolution,
these results need to be viewed with caution. Particle in cell models
can incorporate feedback and in one scenario suggest that acceleration
can be limited by the energetic particles reaching the condition for
firehose marginal stability. Contemporary issues such as footpoint
particle acceleration are also discussed. It is also noted that the
idea of a "standard flare model" is ill-conceived when the entire
distribution of flare energies is considered.
---------------------------------------------------------
Title: Turbulence, Magnetic Reconnection in Turbulent Fluids and
Energetic Particle Acceleration
Authors: Lazarian, A.; Vlahos, L.; Kowal, G.; Yan, H.; Beresnyak,
A.; de Gouveia Dal Pino, E. M.
2012SSRv..173..557L Altcode: 2012SSRv..tmp...90L; 2012SSRv..tmp...86L; 2012arXiv1211.0008L
Turbulence is ubiquitous in astrophysics. It radically changes
many astrophysical phenomena, in particular, the propagation and
acceleration of cosmic rays. We present the modern understanding of
compressible magnetohydrodynamic (MHD) turbulence, in particular its
decomposition into Alfvén, slow and fast modes, discuss the density
structure of turbulent subsonic and supersonic media, as well as other
relevant regimes of astrophysical turbulence. All this information is
essential for understanding the energetic particle acceleration that we
discuss further in the review. For instance, we show how fast and slow
modes accelerate energetic particles through the second order Fermi
acceleration, while density fluctuations generate magnetic fields
in pre-shock regions enabling the first order Fermi acceleration of
high energy cosmic rays. Very importantly, however, the first order
Fermi cosmic ray acceleration is also possible in sites of magnetic
reconnection. In the presence of turbulence this reconnection gets
fast and we present numerical evidence supporting the predictions of
the Lazarian and Vishniac (Astrophys. J. 517:700-718, 1999) model of
fast reconnection. The efficiency of this process suggests that magnetic
reconnection can release substantial amounts of energy in short periods
of time. As the particle tracing numerical simulations show that the
particles can be efficiently accelerated during the reconnection,
we argue that the process of magnetic reconnection may be much more
important for particle acceleration than it is currently accepted. In
particular, we discuss the acceleration arising from reconnection as
a possible origin of the anomalous cosmic rays measured by Voyagers
as well as the origin cosmic ray excess in the direction of Heliotail.
---------------------------------------------------------
Title: Design concepts for the Cherenkov Telescope Array CTA: an
advanced facility for ground-based high-energy gamma-ray astronomy
Authors: Actis, M.; Agnetta, G.; Aharonian, F.; Akhperjanian,
A.; Aleksić, J.; Aliu, E.; Allan, D.; Allekotte, I.; Antico, F.;
Antonelli, L. A.; Antoranz, P.; Aravantinos, A.; Arlen, T.; Arnaldi,
H.; Artmann, S.; Asano, K.; Asorey, H.; Bähr, J.; Bais, A.; Baixeras,
C.; Bajtlik, S.; Balis, D.; Bamba, A.; Barbier, C.; Barceló, M.;
Barnacka, A.; Barnstedt, J.; Barres de Almeida, U.; Barrio, J. A.;
Basso, S.; Bastieri, D.; Bauer, C.; Becerra, J.; Becherini, Y.;
Bechtol, K.; Becker, J.; Beckmann, V.; Bednarek, W.; Behera, B.;
Beilicke, M.; Belluso, M.; Benallou, M.; Benbow, W.; Berdugo, J.;
Berger, K.; Bernardino, T.; Bernlöhr, K.; Biland, A.; Billotta, S.;
Bird, T.; Birsin, E.; Bissaldi, E.; Blake, S.; Blanch, O.; Bobkov,
A. A.; Bogacz, L.; Bogdan, M.; Boisson, C.; Boix, J.; Bolmont,
J.; Bonanno, G.; Bonardi, A.; Bonev, T.; Borkowski, J.; Botner, O.;
Bottani, A.; Bourgeat, M.; Boutonnet, C.; Bouvier, A.; Brau-Nogué, S.;
Braun, I.; Bretz, T.; Briggs, M. S.; Brun, P.; Brunetti, L.; Buckley,
J. H.; Bugaev, V.; Bühler, R.; Bulik, T.; Busetto, G.; Buson, S.;
Byrum, K.; Cailles, M.; Cameron, R.; Canestrari, R.; Cantu, S.;
Carmona, E.; Carosi, A.; Carr, J.; Carton, P. H.; Casiraghi, M.;
Castarede, H.; Catalano, O.; Cavazzani, S.; Cazaux, S.; Cerruti,
B.; Cerruti, M.; Chadwick, P. M.; Chiang, J.; Chikawa, M.; Cieślar,
M.; Ciesielska, M.; Cillis, A.; Clerc, C.; Colin, P.; Colomé, J.;
Compin, M.; Conconi, P.; Connaughton, V.; Conrad, J.; Contreras, J. L.;
Coppi, P.; Corlier, M.; Corona, P.; Corpace, O.; Corti, D.; Cortina,
J.; Costantini, H.; Cotter, G.; Courty, B.; Couturier, S.; Covino,
S.; Croston, J.; Cusumano, G.; Daniel, M. K.; Dazzi, F.; de Angelis,
A.; de Cea Del Pozo, E.; de Gouveia Dal Pino, E. M.; de Jager, O.;
de La Calle Pérez, I.; de La Vega, G.; de Lotto, B.; de Naurois,
M.; de Oña Wilhelmi, E.; de Souza, V.; Decerprit, B.; Deil, C.;
Delagnes, E.; Deleglise, G.; Delgado, C.; Dettlaff, T.; di Paolo,
A.; di Pierro, F.; Díaz, C.; Dick, J.; Dickinson, H.; Digel, S. W.;
Dimitrov, D.; Disset, G.; Djannati-Ataï, A.; Doert, M.; Domainko,
W.; Dorner, D.; Doro, M.; Dournaux, J. -L.; Dravins, D.; Drury, L.;
Dubois, F.; Dubois, R.; Dubus, G.; Dufour, C.; Durand, D.; Dyks,
J.; Dyrda, M.; Edy, E.; Egberts, K.; Eleftheriadis, C.; Elles, S.;
Emmanoulopoulos, D.; Enomoto, R.; Ernenwein, J. -P.; Errando, M.;
Etchegoyen, A.; Falcone, A. D.; Farakos, K.; Farnier, C.; Federici,
S.; Feinstein, F.; Ferenc, D.; Fillin-Martino, E.; Fink, D.; Finley,
C.; Finley, J. P.; Firpo, R.; Florin, D.; Föhr, C.; Fokitis, E.;
Font, Ll.; Fontaine, G.; Fontana, A.; Förster, A.; Fortson, L.;
Fouque, N.; Fransson, C.; Fraser, G. W.; Fresnillo, L.; Fruck, C.;
Fujita, Y.; Fukazawa, Y.; Funk, S.; Gäbele, W.; Gabici, S.; Gadola,
A.; Galante, N.; Gallant, Y.; García, B.; García López, R. J.;
Garrido, D.; Garrido, L.; Gascón, D.; Gasq, C.; Gaug, M.; Gaweda,
J.; Geffroy, N.; Ghag, C.; Ghedina, A.; Ghigo, M.; Gianakaki, E.;
Giarrusso, S.; Giavitto, G.; Giebels, B.; Giro, E.; Giubilato, P.;
Glanzman, T.; Glicenstein, J. -F.; Gochna, M.; Golev, V.; Gómez
Berisso, M.; González, A.; González, F.; Grañena, F.; Graciani,
R.; Granot, J.; Gredig, R.; Green, A.; Greenshaw, T.; Grimm, O.;
Grube, J.; Grudzińska, M.; Grygorczuk, J.; Guarino, V.; Guglielmi,
L.; Guilloux, F.; Gunji, S.; Gyuk, G.; Hadasch, D.; Haefner, D.;
Hagiwara, R.; Hahn, J.; Hallgren, A.; Hara, S.; Hardcastle, M. J.;
Hassan, T.; Haubold, T.; Hauser, M.; Hayashida, M.; Heller, R.; Henri,
G.; Hermann, G.; Herrero, A.; Hinton, J. A.; Hoffmann, D.; Hofmann,
W.; Hofverberg, P.; Horns, D.; Hrupec, D.; Huan, H.; Huber, B.; Huet,
J. -M.; Hughes, G.; Hultquist, K.; Humensky, T. B.; Huppert, J. -F.;
Ibarra, A.; Illa, J. M.; Ingjald, J.; Inoue, Y.; Inoue, S.; Ioka, K.;
Jablonski, C.; Jacholkowska, A.; Janiak, M.; Jean, P.; Jensen, H.;
Jogler, T.; Jung, I.; Kaaret, P.; Kabuki, S.; Kakuwa, J.; Kalkuhl,
C.; Kankanyan, R.; Kapala, M.; Karastergiou, A.; Karczewski, M.;
Karkar, S.; Karlsson, N.; Kasperek, J.; Katagiri, H.; Katarzyński, K.;
Kawanaka, N.; Kȩdziora, B.; Kendziorra, E.; Khélifi, B.; Kieda, D.;
Kifune, T.; Kihm, T.; Klepser, S.; Kluźniak, W.; Knapp, J.; Knappy,
A. R.; Kneiske, T.; Knödlseder, J.; Köck, F.; Kodani, K.; Kohri,
K.; Kokkotas, K.; Komin, N.; Konopelko, A.; Kosack, K.; Kossakowski,
R.; Kostka, P.; Kotuła, J.; Kowal, G.; Kozioł, J.; Krähenbühl,
T.; Krause, J.; Krawczynski, H.; Krennrich, F.; Kretzschmann, A.;
Kubo, H.; Kudryavtsev, V. A.; Kushida, J.; La Barbera, N.; La Parola,
V.; La Rosa, G.; López, A.; Lamanna, G.; Laporte, P.; Lavalley, C.;
Le Flour, T.; Le Padellec, A.; Lenain, J. -P.; Lessio, L.; Lieunard,
B.; Lindfors, E.; Liolios, A.; Lohse, T.; Lombardi, S.; Lopatin,
A.; Lorenz, E.; Lubiński, P.; Luz, O.; Lyard, E.; Maccarone, M. C.;
Maccarone, T.; Maier, G.; Majumdar, P.; Maltezos, S.; Małkiewicz,
P.; Mañá, C.; Manalaysay, A.; Maneva, G.; Mangano, A.; Manigot,
P.; Marín, J.; Mariotti, M.; Markoff, S.; Martínez, G.; Martínez,
M.; Mastichiadis, A.; Matsumoto, H.; Mattiazzo, S.; Mazin, D.; McComb,
T. J. L.; McCubbin, N.; McHardy, I.; Medina, C.; Melkumyan, D.; Mendes,
A.; Mertsch, P.; Meucci, M.; Michałowski, J.; Micolon, P.; Mineo,
T.; Mirabal, N.; Mirabel, F.; Miranda, J. M.; Mirzoyan, R.; Mizuno,
T.; Moal, B.; Moderski, R.; Molinari, E.; Monteiro, I.; Moralejo, A.;
Morello, C.; Mori, K.; Motta, G.; Mottez, F.; Moulin, E.; Mukherjee,
R.; Munar, P.; Muraishi, H.; Murase, K.; Murphy, A. Stj.; Nagataki,
S.; Naito, T.; Nakamori, T.; Nakayama, K.; Naumann, C.; Naumann, D.;
Nayman, P.; Nedbal, D.; Niedźwiecki, A.; Niemiec, J.; Nikolaidis,
A.; Nishijima, K.; Nolan, S. J.; Nowak, N.; O'Brien, P. T.; Ochoa,
I.; Ohira, Y.; Ohishi, M.; Ohka, H.; Okumura, A.; Olivetto, C.; Ong,
R. A.; Orito, R.; Orr, M.; Osborne, J. P.; Ostrowski, M.; Otero, L.;
Otte, A. N.; Ovcharov, E.; Oya, I.; Oziȩbło, A.; Paiano, S.; Pallota,
J.; Panazol, J. L.; Paneque, D.; Panter, M.; Paoletti, R.; Papyan,
G.; Paredes, J. M.; Pareschi, G.; Parsons, R. D.; Paz Arribas, M.;
Pedaletti, G.; Pepato, A.; Persic, M.; Petrucci, P. O.; Peyaud,
B.; Piechocki, W.; Pita, S.; Pivato, G.; Płatos, Ł.; Platzer,
R.; Pogosyan, L.; Pohl, M.; Pojmański, G.; Ponz, J. D.; Potter,
W.; Prandini, E.; Preece, R.; Prokoph, H.; Pühlhofer, G.; Punch,
M.; Quel, E.; Quirrenbach, A.; Rajda, P.; Rando, R.; Rataj, M.;
Raue, M.; Reimann, C.; Reimann, O.; Reimer, A.; Reimer, O.; Renaud,
M.; Renner, S.; Reymond, J. -M.; Rhode, W.; Ribó, M.; Ribordy,
M.; Rico, J.; Rieger, F.; Ringegni, P.; Ripken, J.; Ristori, P.;
Rivoire, S.; Rob, L.; Rodriguez, S.; Roeser, U.; Romano, P.; Romero,
G. E.; Rosier-Lees, S.; Rovero, A. C.; Roy, F.; Royer, S.; Rudak, B.;
Rulten, C. B.; Ruppel, J.; Russo, F.; Ryde, F.; Sacco, B.; Saggion, A.;
Sahakian, V.; Saito, K.; Saito, T.; Sakaki, N.; Salazar, E.; Salini,
A.; Sánchez, F.; Sánchez Conde, M. Á.; Santangelo, A.; Santos,
E. M.; Sanuy, A.; Sapozhnikov, L.; Sarkar, S.; Scalzotto, V.; Scapin,
V.; Scarcioffolo, M.; Schanz, T.; Schlenstedt, S.; Schlickeiser, R.;
Schmidt, T.; Schmoll, J.; Schroedter, M.; Schultz, C.; Schultze, J.;
Schulz, A.; Schwanke, U.; Schwarzburg, S.; Schweizer, T.; Seiradakis,
J.; Selmane, S.; Seweryn, K.; Shayduk, M.; Shellard, R. C.; Shibata,
T.; Sikora, M.; Silk, J.; Sillanpää, A.; Sitarek, J.; Skole, C.;
Smith, N.; Sobczyńska, D.; Sofo Haro, M.; Sol, H.; Spanier, F.; Spiga,
D.; Spyrou, S.; Stamatescu, V.; Stamerra, A.; Starling, R. L. C.;
Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Steiner, S.; Stergioulas,
N.; Sternberger, R.; Stinzing, F.; Stodulski, M.; Straumann, U.;
Suárez, A.; Suchenek, M.; Sugawara, R.; Sulanke, K. H.; Sun, S.;
Supanitsky, A. D.; Sutcliffe, P.; Szanecki, M.; Szepieniec, T.;
Szostek, A.; Szymkowiak, A.; Tagliaferri, G.; Tajima, H.; Takahashi,
H.; Takahashi, K.; Takalo, L.; Takami, H.; Talbot, R. G.; Tam, P. H.;
Tanaka, M.; Tanimori, T.; Tavani, M.; Tavernet, J. -P.; Tchernin, C.;
Tejedor, L. A.; Telezhinsky, I.; Temnikov, P.; Tenzer, C.; Terada,
Y.; Terrier, R.; Teshima, M.; Testa, V.; Tibaldo, L.; Tibolla, O.;
Tluczykont, M.; Todero Peixoto, C. J.; Tokanai, F.; Tokarz, M.; Toma,
K.; Torres, D. F.; Tosti, G.; Totani, T.; Toussenel, F.; Vallania,
P.; Vallejo, G.; van der Walt, J.; van Eldik, C.; Vandenbroucke, J.;
Vankov, H.; Vasileiadis, G.; Vassiliev, V. V.; Vegas, I.; Venter, L.;
Vercellone, S.; Veyssiere, C.; Vialle, J. P.; Videla, M.; Vincent,
P.; Vink, J.; Vlahakis, N.; Vlahos, L.; Vogler, P.; Vollhardt, A.;
Volpe, F.; von Gunten, H. P.; Vorobiov, S.; Wagner, S.; Wagner,
R. M.; Wagner, B.; Wakely, S. P.; Walter, P.; Walter, R.; Warwick,
R.; Wawer, P.; Wawrzaszek, R.; Webb, N.; Wegner, P.; Weinstein, A.;
Weitzel, Q.; Welsing, R.; Wetteskind, H.; White, R.; Wierzcholska,
A.; Wilkinson, M. I.; Williams, D. A.; Winde, M.; Wischnewski, R.;
Wiśniewski, Ł.; Wolczko, A.; Wood, M.; Xiong, Q.; Yamamoto, T.;
Yamaoka, K.; Yamazaki, R.; Yanagita, S.; Yoffo, B.; Yonetani, M.;
Yoshida, A.; Yoshida, T.; Yoshikoshi, T.; Zabalza, V.; Zagdański,
A.; Zajczyk, A.; Zdziarski, A.; Zech, A.; Ziȩtara, K.; Ziółkowski,
P.; Zitelli, V.; Zychowski, P.
2011ExA....32..193A Altcode: 2011ExA...tmp..121A; 2010arXiv1008.3703C
Ground-based gamma-ray astronomy has had a major breakthrough with
the impressive results obtained using systems of imaging atmospheric
Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge
potential in astrophysics, particle physics and cosmology. CTA is
an international initiative to build the next generation instrument,
with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV
range and the extension to energies well below 100 GeV and above 100
TeV. CTA will consist of two arrays (one in the north, one in the south)
for full sky coverage and will be operated as open observatory. The
design of CTA is based on currently available technology. This document
reports on the status and presents the major design concepts of CTA.
---------------------------------------------------------
Title: Recent Advances in Understanding Particle Acceleration
Processes in Solar Flares
Authors: Zharkova, V. V.; Arzner, K.; Benz, A. O.; Browning, P.;
Dauphin, C.; Emslie, A. G.; Fletcher, L.; Kontar, E. P.; Mann, G.;
Onofri, M.; Petrosian, V.; Turkmani, R.; Vilmer, N.; Vlahos, L.
2011SSRv..159..357Z Altcode: 2011SSRv..tmp..156Z; 2011SSRv..tmp..249Z; 2011SSRv..tmp..232Z;
2011arXiv1110.2359Z; 2011SSRv..tmp..278Z
We review basic theoretical concepts in particle acceleration,
with particular emphasis on processes likely to occur in regions of
magnetic reconnection. Several new developments are discussed, including
detailed studies of reconnection in three-dimensional magnetic field
configurations (e.g., current sheets, collapsing traps, separatrix
regions) and stochastic acceleration in a turbulent environment. Fluid,
test-particle, and particle-in-cell approaches are used and results
compared. While these studies show considerable promise in accounting
for the various observational manifestations of solar flares, they
are limited by a number of factors, mostly relating to available
computational power. Not the least of these issues is the need to
explicitly incorporate the electrodynamic feedback of the accelerated
particles themselves on the environment in which they are accelerated. A
brief prognosis for future advancement is offered.
---------------------------------------------------------
Title: Simulating flaring events in complex active regions driven
by observed magnetograms
Authors: Dimitropoulou, M.; Isliker, H.; Vlahos, L.; Georgoulis, M. K.
2011A&A...529A.101D Altcode: 2011arXiv1102.2352D
Context. We interpret solar flares as events originating in active
regions that have reached the self organized critical state, by using
a refined cellular automaton model with initial conditions derived
from observations. <BR /> Aims: We investigate whether the system,
with its imposed physical elements, reaches a self organized critical
state and whether well-known statistical properties of flares,
such as scaling laws observed in the distribution functions of
characteristic parameters, are reproduced after this state has been
reached. <BR /> Methods: To investigate whether the distribution
functions of total energy, peak energy and event duration follow
the expected scaling laws, we first applied a nonlinear force-free
extrapolation that reconstructs the three-dimensional magnetic
fields from two-dimensional vector magnetograms. We then locate
magnetic discontinuities exceeding a threshold in the Laplacian of the
magnetic field. These discontinuities are relaxed in local diffusion
events, implemented in the form of cellular automaton evolution
rules. Subsequent loading and relaxation steps lead the system to
self organized criticality, after which the statistical properties
of the simulated events are examined. Physical requirements, such
as the divergence-free condition for the magnetic field vector, are
approximately imposed on all elements of the model. <BR /> Results:
Our results show that self organized criticality is indeed reached
when applying specific loading and relaxation rules. Power-law indices
obtained from the distribution functions of the modeled flaring events
are in good agreement with observations. Single power laws (peak and
total flare energy) are obtained, as are power laws with exponential
cutoff and double power laws (flare duration). The results are also
compared with observational X-ray data from the GOES satellite for our
active-region sample. <BR /> Conclusions: We conclude that well-known
statistical properties of flares are reproduced after the system
has reached self organized criticality. A significant enhancement
of our refined cellular automaton model is that it commences the
simulation from observed vector magnetograms, thus facilitating
energy calculation in physical units. The model described in this
study remains consistent with fundamental physical requirements,
and imposes physically meaningful driving and redistribution rules.
---------------------------------------------------------
Title: Simulating Flaring Events via an Intelligent Cellular Automata
Mechanism
Authors: Dimitropoulou, M.; Vlahos, L.; Isliker, H.; Georgoulis, M.
2010ASPC..424...28D Altcode:
We simulate flaring events through a Cellular Automaton (CA) model,
in which, for the first time, we use observed vector magnetograms as
initial conditions. After non-linear force free extrapolation of the
magnetic field from the vector magnetograms, we identify magnetic
discontinuities, using two alternative criteria: (1) the average
magnetic field gradient, or (2) the normalized magnetic field curl
(i.e. the current). Magnetic discontinuities are identified at the
grid-sites where the magnetic field gradient or curl exceeds a specified
threshold. We then relax the magnetic discontinuities according to
the rules of Lu and Hamilton (1991) or Lu et al. (1993), i.e. we
redistribute the magnetic field locally so that the discontinuities
disappear. In order to simulate the flaring events, we consider
several alternative scenarios with regard to: (1) The threshold
above which magnetic discontinuities are identified (applying low,
high, and height-dependent threshold values); (2) The driving process
that occasionally causes new discontinuities (at randomly chosen grid
sites, magnetic field increments are added that are perpendicular (or
may-be also parallel) to the existing magnetic field). We address the
question whether the coronal active region magnetic fields can indeed
be considered to be in the state of self-organized criticality (SOC).
---------------------------------------------------------
Title: Local re-acceleration and a modified thick target model of
solar flare electrons
Authors: Brown, J. C.; Turkmani, R.; Kontar, E. P.; MacKinnon, A. L.;
Vlahos, L.
2009A&A...508..993B Altcode: 2009arXiv0909.4243B
Context: The collisional thick target model (CTTM) of solar hard
X-ray (HXR) bursts has become an almost “standard model” of
flare impulsive phase energy transport and radiation. However, it
faces various problems in the light of recent data, particularly the
high electron beam density and anisotropy it involves.<BR /> Aims: We
consider how photon yield per electron can be increased, and hence fast
electron beam intensity requirements reduced, by local re-acceleration
of fast electrons throughout the HXR source itself, after injection.<BR
/> Methods: We show parametrically that, if net re-acceleration rates
due to e.g. waves or local current sheet electric (E) fields are a
significant fraction of collisional loss rates, electron lifetimes, and
hence the net radiative HXR output per electron can be substantially
increased over the CTTM values. In this local re-acceleration thick
target model (LRTTM) fast electron number requirements and anisotropy
are thus reduced. One specific possible scenario involving such
re-acceleration is discussed, viz, a current sheet cascade (CSC) in a
randomly stressed magnetic loop.<BR /> Results: Combined MHD and test
particle simulations show that local E fields in CSCs can efficiently
accelerate electrons in the corona and and re-accelerate them after
injection into the chromosphere. In this HXR source scenario, rapid
synchronisation and variability of impulsive footpoint emissions can
still occur since primary electron acceleration is in the high Alfvén
speed corona with fast re-acceleration in chromospheric CSCs. It is
also consistent with the energy-dependent time-of-flight delays in
HXR features.<BR /> Conclusions: Including electron re-acceleration in
the HXR source allows an LRTTM modification of the CTTM in which beam
density and anisotropy are much reduced, and alleviates theoretical
problems with the CTTM, while making it more compatible with radio and
interplanetary electron numbers. The LRTTM is, however, different in
some respects such as spatial distribution of atmospheric heating by
fast electrons.
---------------------------------------------------------
Title: The correlation of fractal structures in the photospheric
and the coronal magnetic field
Authors: Dimitropoulou, M.; Georgoulis, M.; Isliker, H.; Vlahos, L.;
Anastasiadis, A.; Strintzi, D.; Moussas, X.
2009A&A...505.1245D Altcode: 2009arXiv0908.3950D
Context: This work examines the relation between the fractal properties
of the photospheric magnetic patterns and those of the coronal
magnetic fields in solar active regions. <BR />Aims: We investigate
whether there is any correlation between the fractal dimensions of
the photospheric structures and the magnetic discontinuities formed in
the corona. <BR />Methods: To investigate the connection between the
photospheric and coronal complexity, we used a nonlinear force-free
extrapolation method that reconstructs the 3d magnetic fields using 2d
observed vector magnetograms as boundary conditions. We then located
the magnetic discontinuities, which are considered as spatial proxies
of reconnection-related instabilities. These discontinuities form
well-defined volumes, called here unstable volumes. We calculated
the fractal dimensions of these unstable volumes and compared them
to the fractal dimensions of the boundary vector magnetograms. <BR
/>Results: Our results show no correlation between the fractal
dimensions of the observed 2d photospheric structures and the
extrapolated unstable volumes in the corona, when nonlinear force-free
extrapolation is used. This result is independent of efforts to
(1) bring the photospheric magnetic fields closer to a nonlinear
force-free equilibrium and (2) omit the lower part of the modeled
magnetic field volume that is almost completely filled by unstable
volumes. A significant correlation between the fractal dimensions of
the photospheric and coronal magnetic features is only observed at the
zero level (lower limit) of approximation of a current-free (potential)
magnetic field extrapolation. <BR />Conclusions: We conclude that
the complicated transition from photospheric non-force-free fields
to coronal force-free ones hampers any direct correlation between
the fractal dimensions of the 2d photospheric patterns and their
3d counterparts in the corona at the nonlinear force-free limit,
which can be considered as a second level of approximation in this
study. Correspondingly, in the zero and first levels of approximation,
namely, the potential and linear force-free extrapolation, respectively,
we reveal a significant correlation between the fractal dimensions of
the photospheric and coronal structures, which can be attributed to the
lack of electric currents or to their purely field-aligned orientation.
---------------------------------------------------------
Title: The Solar Flare: A Strongly Turbulent Particle Accelerator
Authors: Vlahos, L.; Krucker, S.; Cargill, P.
2009LNP...778..157V Altcode:
The topics of explosive magnetic energy release on a large scale
(a solar flare) and particle acceleration during such an event are
rarely discussed together in the same article. Many discussions of
magnetohydrodynamic (MHD) mod- eling of solar flares and/or CMEs
have appeared (see [143] and references therein) and usually address
large-scale destabilization of the coronal mag- netic field. Particle
acceleration in solar flares has also been discussed exten- sively
[74, 164, 116, 166, 87, 168, 95, 122, 35] with the main emphasis being
on the actual mechanisms for acceleration (e.g., shocks, turbulence,
DC electric fields) rather than the global magnetic context in which
the acceleration takes place.
---------------------------------------------------------
Title: Solar and Stellar Active Regions
Authors: Vlahos, Loukas
2009ASSP....8..423V Altcode: 2009chas.book..423V
No abstract at ADS
---------------------------------------------------------
Title: Turbulence in Space Plasmas by Peter Cargill, Loukas
Vlahos. Lecture Notes in Physics, Vol. 778. Berlin: Springer, 2009.
Authors: Cargill, Peter; Vlahos, Loukas
2009LNP...778.....C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Hard X-ray emission from the solar corona
Authors: Krucker, S.; Battaglia, M.; Cargill, P. J.; Fletcher, L.;
Hudson, H. S.; MacKinnon, A. L.; Masuda, S.; Sui, L.; Tomczak, M.;
Veronig, A. L.; Vlahos, L.; White, S. M.
2008A&ARv..16..155K Altcode: 2008A&ARv.tmp....8K
This review surveys hard X-ray emissions of non-thermal electrons in the
solar corona. These electrons originate in flares and flare-related
processes. Hard X-ray emission is the most direct diagnostic of
electron presence in the corona, and such observations provide
quantitative determinations of the total energy in the non-thermal
electrons. The most intense flare emissions are generally observed
from the chromosphere at footpoints of magnetic loops. Over the years,
however, many observations of hard X-ray and even γ-ray emission
directly from the corona have also been reported. These coronal sources
are of particular interest as they occur closest to where the electron
acceleration is thought to occur. Prior to the actual direct imaging
observations, disk occultation was usually required to study coronal
sources, resulting in limited physical information. Now RHESSI has
given us a systematic view of coronal sources that combines high
spatial and spectral resolution with broad energy coverage and high
sensitivity. Despite the low density and hence low bremsstrahlung
efficiency of the corona, we now detect coronal hard X-ray emissions
from sources in all phases of solar flares. Because the physical
conditions in such sources may differ substantially from those of
the usual “footpoint” emission regions, we take the opportunity
to revisit the physics of hard X-radiation and relevant theories of
particle acceleration.
---------------------------------------------------------
Title: Imprints of cosmic strings on the cosmological gravitational
wave background
Authors: Kleidis, K.; Papadopoulos, D. B.; Verdaguer, E.; Vlahos, L.
2008PhRvD..78b4027K Altcode: 2008arXiv0806.2999K
The equation which governs the temporal evolution of a gravitational
wave (GW) in curved space-time can be treated as the Schrödinger
equation for a particle moving in the presence of an effective
potential. When GWs propagate in an expanding universe with constant
effective potential, there is a critical value (k<SUB>c</SUB>) of the
comoving wave number which discriminates the metric perturbations into
oscillating (k>k<SUB>c</SUB>) and nonoscillating (k<k<SUB>c</SUB>)
modes. As a consequence, if the nonoscillatory modes are outside the
horizon they do not freeze out. The effective potential is reduced
to a nonvanishing constant in a cosmological model which is driven
by a two-component fluid, consisting of radiation (dominant) and
cosmic strings (subdominant). It is known that the cosmological
evolution gradually results in the scaling of a cosmic-string
network and, therefore, after some time (Δτ) the Universe becomes
radiation dominated. The evolution of the nonoscillatory GW modes
during Δτ (while they were outside the horizon), results in the
distortion of the GW power spectrum from what it is anticipated in
a pure radiation model, at present-time frequencies in the range
10<SUP>-16</SUP>Hz<f≲10<SUP>5</SUP>Hz.
---------------------------------------------------------
Title: Solar and Stellar Active Regions:Cosmic laboratories for the
study of Complexity
Authors: Vlahos, Loukas
2008arXiv0803.3158V Altcode:
Solar active regions are driven dissipative dynamical systems. The
turbulent convection zone forces new magnetic flux tubes to rise
above the photosphere and shuffles the magnetic fields which are
already above the photosphere. The driven 3D active region responds
to the driver with the formation of Thin Current Sheets in all scales
and releases impulsively energy, when special thresholds are met,
on the form of nano-, micro-, flares and large scale coronal mass
ejections. It has been documented that active regions form self
similar structures with area Probability Distribution Functions
(PDF's) following power laws and with fractal dimensions ranging from
$1.2-1.7$. The energy release on the other hand follows a specific
energy distribution law $f(E_T)\sim E_T^{-a}$, where $a \sim 1.6-1.8$
and $E_T$ is the total energy released. A possible explanation for the
statistical properties of the magnetogrms and the energy release by
the active region is that the magnetic field formation follows rules
analogous to \textbf{percolating models}, and the 3D magnetic fields
above the photosphere reach a \textbf{Self Organized Critical (SOC)
state}. The implications of these findings on the acceleration of
energetic particles during impulsive phenomena will briefly be outlined.
---------------------------------------------------------
Title: Dynamo Effects in Magnetized Ideal Plasma Cosmologies
Authors: Kleidis, Kostas; Kuiroukidis, Apostolos; Papadopoulos,
Demetrios; Vlahos, Loukas
2008IJMPA..23.1697K Altcode: 2007arXiv0712.4239K
The excitation of cosmological perturbations in an anisotropic
cosmological model and in the presence of a homogeneous magnetic
field has been studied, using the ideal magnetohydrodynamic
(MHD) equations. In this case, the system of partial differential
equations which governs the evolution of the magnetized cosmological
perturbations can be solved analytically. Our results verify that
fast-magnetosonic modes propagating normal to the magnetic field,
are excited. But, what is most important, is that, at late times, the
magnetic-induction contrast (δB/B) grows, resulting in the enhancement
of the ambient magnetic field. This process can be particularly favored
by condensations, formed within the plasma fluid due to gravitational
instabilities.
---------------------------------------------------------
Title: Gravitomagnetic Instabilities in Anisotropically Expanding
Fluids
Authors: Kleidis, Kostas; Kuiroukidis, Apostolos; Papadopoulos,
Demetrios B.; Vlahos, Loukas
2008IJMPA..23.4467K Altcode: 2008arXiv0806.4362K
Gravitational instabilities in a magnetized Friedman-Robertson-Walker
(FRW) universe, in which the magnetic field was assumed to be too
weak to destroy the isotropy of the model, are known and have been
studied in the past. Accordingly, it became evident that the external
magnetic field disfavors the perturbations' growth, suppressing the
corresponding rate by an amount proportional to its strength. However,
the spatial isotropy of the FRW universe is not compatible with
the presence of large-scale magnetic fields. Therefore, in this
paper we use the general-relativistic version of the (linearized)
perturbed magnetohydrodynamic equations with and without resistivity,
to discuss a generalized Jeans criterion and the potential formation of
density condensations within a class of homogeneous and anisotropically
expanding, self-gravitating, magnetized fluids in curved space-time. We
find that, for a wide variety of anisotropic cosmological models,
gravitomagnetic instabilities can lead to subhorizontal, magnetized
condensations. In the nonresistive case, the power spectrum of the
unstable cosmological perturbations suggests that most of the power is
concentrated on large scales (small k), very close to the horizon. On
the other hand, in a resistive medium, the critical wave-numbers so
obtained, exhibit a delicate dependence on resistivity, resulting in
the reduction of the corresponding Jeans lengths to smaller scales
(well bellow the horizon) than the nonresistive ones, while increasing
the range of cosmological models which admit such an instability.
---------------------------------------------------------
Title: Magnetohydrodynamics and Plasma Cosmology
Authors: Kleidis, Kostas; Kuiroukidis, Apostolos; Papadopoulos,
Demetrios; Vlahos, Loukas
2007IJTP...46.2283K Altcode: 2005gr.qc....12131K; 2007IJTP..tmp..132K; 2007IJTP..tmp..208K
We study the linear magnetohydrodynamic (MHD) equations, both in the
Newtonian and the general-relativistic limit, as regards a viscous
magnetized fluid of finite conductivity and discuss instability
criteria. In addition, we explore the excitation of cosmological
perturbations in anisotropic spacetimes, in the presence of an ambient
magnetic field. Acoustic, electromagnetic (e/m) and fast-magnetosonic
modes, propagating normal to the magnetic field, can be excited,
resulting in several implications of cosmological significance.
---------------------------------------------------------
Title: Summary of Joint Discussion 1
Authors: Vlahos, Loukas
2007HiA....14..104V Altcode:
We review the main ideas discussed during the meeting and propose
methods for a new generation of space accelerators
---------------------------------------------------------
Title: Excitation of MHD waves in magnetized anisotropic cosmologies
Authors: Kuiroukidis, A.; Kleidis, K.; Papadopoulos, D. B.; Vlahos, L.
2007A&A...471..409K Altcode: 2007arXiv0705.2194K
The excitation of cosmological perturbations in an anisotropic
cosmological model and in the presence of a homogeneous magnetic
field was studied, using the resistive magnetohydrodynamic (MHD)
equations. We have shown that fast-magnetosonic modes, propagating
normal to the magnetic field, grow exponentially and saturate at high
values, due to the resistivity. We also demonstrate that Jeans-like
instabilities can be enhanced inside a resistive fluid and that the
formation of condensations influence the growing magnetosonic waves.
---------------------------------------------------------
Title: High energy particle transport in stochastic magnetic fields
in the solar corona
Authors: Gkioulidou, M.; Zimbardo, G.; Pommois, P.; Veltri, P.;
Vlahos, L.
2007A&A...462.1113G Altcode:
Aims:We study energetic particle transport in the solar corona in the
presence of magnetic fluctuations by analyzing the motion of protons
injected at the center of a model coronal loop. <BR />Methods: We
set up a numerical realization of magnetic turbulence, in which the
magnetic fluctuations are represented by a Fourier expansion with
random phases. We perform test particle simulations by varying the
turbulence correlation length λ, the turbulence level, and the proton
energy. Coulomb collisions are neglected. <BR />Results: For large λ,
the ratio ρ/λ (with ρ the Larmor radius) is small, and the magnetic
moment is conserved. In this case, a fraction of the injected protons,
which grow with the fluctuation level, are trapped at the top of the
magnetic loop, near the injection region, by magnetic mirroring due to
the magnetic fluctuations. The rest of the protons propagate freely
along B, corresponding to nearly ballistic transport. Decreasing λ,
that is, increasing the ratio ρ/λ, the magnetic moment is no longer
well conserved, and pitch angle diffusion progressively sets in. Pitch
angle diffusion leads to a decrease in the trapped population and
progressively changes proton transport from ballistic to superdiffusive,
and finally, for small λ, to diffusive. <BR />Conclusions: .Particle
mirroring by magnetic turbulence makes for compact trapping regions. The
particle dynamics inside the magnetic loop is non-Gaussian and the
statistical description of transport properties requires the use of
such ideas as the Lévy random walk.
---------------------------------------------------------
Title: Magnetic Complexity, Fragmentation, Particle Acceleration
and Radio Emission from the Sun
Authors: Vlahos, Loukas
2007LNP...725...15V Altcode:
The most popular flare model used to explain the energy release,
particle acceleration and radio emission is based on the following
assumptions: (1) The formation of a current sheet above a magnetic loop,
(2) The stochastic acceleration of particles in the current sheet at
the helmet of the loop, (3) the transport and trapping of particles
inside the flaring loop. We review the observational consequences of the
above model and try to generalize by putting forward a new suggestion,
namely assuming that a complex active region driven by the photospheric
motions forms naturally a large number of stochastic current sheets that
accelerate particles, which in turn can be trapped or move along complex
field line structures. The emphasis will be placed on the efficiency and
the observational tests of the different models proposed for a flare.
---------------------------------------------------------
Title: Particle Acceleration in a Three-Dimensional Model of
Reconnecting Coronal Magnetic Fields
Authors: Cargill, Peter J.; Vlahos, Loukas; Turkmani, Rim; Galsgaard,
Klaus; Isliker, Heinz
2007sdeh.book..249C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Interaction of gravitational waves with strongly magnetized
plasmas
Authors: Isliker, Heinz; Sandberg, Ingmar; Vlahos, Loukas
2006PhRvD..74j4009I Altcode: 2006astro.ph..3828I
We study the interaction of a gravitational wave (GW) with a plasma
that is strongly magnetized. The GW is considered a small disturbance,
and the plasma is modeled by the general relativistic analogue of the
induction equation of ideal MHD and the single fluid equations. The
equations are specified to two different cases, first to Cartesian
coordinates and a constant background magnetic fields, and second to
spherical coordinates together with a background magnetic field that
decays with the inverse radial distance. The equations are derived
without neglecting any of the nonlinear interaction terms, and the
nonlinear equations are integrated numerically. We find that for
strong magnetic fields of the order of 10<SUP>15</SUP>G the GW excites
electromagnetic plasma waves very close to the magnetosonic mode. The
magnetic and electric field oscillations have very high amplitude, and a
large amount of energy is absorbed from the GW by the electromagnetic
oscillations, of the order of 10<SUP>23</SUP>erg/cm<SUP>3</SUP>
in the case presented here, which, when assuming a relatively
small volume in a star’s magnetosphere as an interaction region,
can yield a total energy of at least 10<SUP>41</SUP>erg and may be
up to 10<SUP>43</SUP>erg. The absorbed energy is proportional to
B<SUB>0</SUB><SUP>2</SUP>, with B<SUB>0</SUB> the background magnetic
field. The energizing of the plasma takes place on fast time scales
of the order of milliseconds. Our results imply that the GW-plasma
interaction is an efficient and important mechanism in magnetar
atmospheres, most prominently close to the star, and, under very
favorable conditions though, it might even be the primary energizing
mechanism behind giant flares.
---------------------------------------------------------
Title: Gyrokinetic electron acceleration in the force-free corona
with anomalous resistivity
Authors: Arzner, K.; Vlahos, L.
2006A&A...454..957A Altcode: 2006astro.ph..4161A
Aims.We numerically explore electron acceleration and coronal heating
by dissipative electric fields.<BR /> Methods: .Electrons are traced
in linear force-free magnetic fields extrapolated from SOHO/MDI
magnetograms, endowed with anomalous resistivity (η) in localized
dissipation regions where the magnetic twist ∇ × hat{{b}} exceeds a
given threshold. Associated with η > 0 is a parallel electric field
{E} = η {j} that can accelerate runaway electrons. In order to gain
observational predictions, we inject electrons inside the dissipation
regions and follow them for several seconds in real time.<BR /> Results:
.Precipitating electrons that leave the simulation system at height
z = 0 are associated with hard X rays, and electrons that escape at
height z ∼ 3× 10<SUP>4</SUP> km are associated with normal-drifting
type IIIs at the local plasma frequency. A third, trapped population
is related to gyrosynchrotron emission. Time profiles and spectra
of all three emissions are calculated, and their dependence on the
geometric model parameters and on η is explored. It is found that
precipitation generally precedes escape by fractions of a second and
that the electrons perform many visits to the dissipation regions
before leaving the simulation system. The electrons impacting z =
0 reach higher energies than the escaping ones, and non-Maxwellian
tails are observed at energies above the largest potential drop across a
single dissipation region. Impact maps at z = 0 show the tendency of the
electrons to arrive at the borders of sunspots of one polarity.<BR />
Conclusions: .Although the magnetograms used here belong to non-flaring
times, so that the simulations refer to nanoflares and "quiescent"
coronal heating, it is conjectured that the same process, on a larger
scale, is responsible for solar flares.
---------------------------------------------------------
Title: High Energy Particle Transport in Stochastic Magnetic Fields
in Solar Coronal Loops
Authors: Gkioulidou, M.; Zimbardo, G.; Pammois, P.; Veltri, P.;
Vlahos, L.
2006ESASP.617E.152G Altcode: 2006soho...17E.152G
No abstract at ADS
---------------------------------------------------------
Title: Particle Acceleration in a Three-Dimensional Model of
Reconnecting Coronal Magnetic Fields
Authors: Cargill, Peter J.; Vlahos, Loukas; Turkmani, Rim; Galsgaard,
Klaus; Isliker, Heinz
2006SSRv..124..249C Altcode: 2006SSRv..tmp..111C
Particle acceleration in large-scale turbulent coronal magnetic fields
is considered. Using test particle calculations, it is shown that
both cellular automata and three dimensional MHD models lead to the
production of relativistic particles on sub-second timescales with
power law distribution functions. In distinction with the monolithic
current sheet models for solar flares, particles gain energy by multiple
interactions with many current sheets. Difficulties that need to be
addressed, such as feedback between particle acceleration and MHD,
are discussed.
---------------------------------------------------------
Title: Particle acceleration in stochastic current sheets in stressed
coronal active regions
Authors: Turkmani, R.; Cargill, P. J.; Galsgaard, K.; Vlahos, L.;
Isliker, H.
2006A&A...449..749T Altcode:
Aims.To perform numerical experiments of particle acceleration in the
complex magnetic and electric field environment of the stressed solar
corona.Methods.The magnetic and electric fields are obtained from a
3-D MHD experiment that resembles a coronal loop with photospheric
regions at both footpoints. Photospheric footpoint motion leads to
the formation of a hierarchy of stochastic current sheets. Particles
(protons and electrons) are traced within these current sheets
starting from a thermal distribution using a relativistic test particle
code.Results.In the corona the particles are subject to acceleration
as well as deceleration, and a considerable portion of them leave the
domain having received a net energy gain. Particles are accelerated to
high energies in a very short time (both species can reach energies
up to 100 GeV within 5 × 10<SUP>-2</SUP> s for electrons and 5
× 10<SUP>-1</SUP> s for protons). The final energy distribution
shows that while one quarter of the particles retain their thermal
distribution, the rest have been accelerated, forming a two-part power
law. Accelerated particles are either trapped within electric field
regions of opposite polarities, or escape the domain mainly through
the footpoints. The particle dynamics are followed in detail and it
is shown how this dynamic affects the time evolution of the system
and the energy distribution. The scaling of these results with time
and length scale is examined and the Bremstrahlung signature of X-ray
photons resulting from escaping particles hitting the chromosphere is
calculated and found to have a main power law part with an index γ =
- 1.8, steeper than observed. Possible resolutions of this discrepency
are discussed.
---------------------------------------------------------
Title: Acceleration of low energy charged particles by gravitational
waves
Authors: Voyatzis, G.; Vlahos, L.; Ichtiaroglou, S.; Papadopoulos, D.
2006PhLA..352..261V Altcode: 2005astro.ph.12192V
The acceleration of charged particles in the presence of a magnetic
field and gravitational waves is under consideration. It is shown
that the weak gravitational waves can cause the acceleration of low
energy particles under appropriate conditions. Such conditions may
be satisfied close to the source of the gravitational waves if the
magnetized plasma is in a turbulent state.
---------------------------------------------------------
Title: Stochastic Acceleration in Turbulent Electric Fields Generated
by 3D Reconnection
Authors: Onofri, Marco; Isliker, Heinz; Vlahos, Loukas
2006PhRvL..96o1102O Altcode: 2006astro.ph..4192O
Electron and proton acceleration in three-dimensional electric and
magnetic fields is studied through test particle simulations. The fields
are obtained by a three-dimensional magnetohydrodynamic simulation
of magnetic reconnection in slab geometry. The nonlinear evolution
of the system is characterized by the growth of many unstable modes
and the initial current sheet is fragmented with formation of small
scale structures. We inject at random points inside the evolving
current sheet a Maxwellian distribution of particles. In a relatively
short time (less than a millisecond) the particles develop a power-law
tail. The acceleration is extremely efficient and the electrons absorb
a large percentage of the available energy in a small fraction of the
characteristic time of the MHD simulation, suggesting that resistive MHD
codes are unable to represent the full extent of particle acceleration.
---------------------------------------------------------
Title: The Effect of Coherent Structures on Stochastic Acceleration
in MHD Turbulence
Authors: Arzner, Kaspar; Knaepen, Bernard; Carati, Daniele; Denewet,
Nicolas; Vlahos, Loukas
2006ApJ...637..322A Altcode: 2005astro.ph..9717A
We investigate the influence of coherent structures on particle
acceleration in the strongly turbulent solar corona. By randomizing
the Fourier phases of a pseudospectral simulation of isotropic
magnetohydrodynamic (MHD) turbulence (Re~300) and tracing collisionless
test protons in both the exact-MHD and phase-randomized fields, it is
found that the phase correlations enhance the acceleration efficiency
during the first adiabatic stage of the acceleration process. The
underlying physical mechanism is identified as the dynamical MHD
alignment of the magnetic field with the electric current, which
favors parallel (resistive) electric fields responsible for initial
injection. Conversely, the alignment of the magnetic field with the
bulk velocity weakens the acceleration by convective electric fields
-uXb at a nonadiabatic stage of the acceleration process. We point out
that nonphysical parallel electric fields in random-phase turbulence
proxies lead to artificial acceleration and that the dynamical MHD
alignment can be taken into account on the level of the joint two-point
function of the magnetic and electric fields and is therefore amenable
to Fokker-Planck descriptions of stochastic acceleration.
---------------------------------------------------------
Title: a Model of Quiet Time Particle Acceleration in Interplanetary
Space
Authors: Lepreti, F.; Isliker, H.; Vlahos, L.; Petraki, K.
2005ESASP.600E.130L Altcode: 2005ESPM...11..130L; 2005dysu.confE.130L
No abstract at ADS
---------------------------------------------------------
Title: AFS dynamics in a short-lived active region
Authors: Zuccarello, F.; Battiato, V.; Contarino, L.; Romano, P.;
Spadaro, D.; Vlahos, L.
2005A&A...442..661Z Altcode:
In the framework of the study on active region emergence, we report the
results obtained from the analysis of the short-lived (7 days) active
region NOAA 10407. The data used were acquired during an observational
campaign carried out with the THEMIS telescope in IPM mode in July 2003,
coordinated with other ground- and space-based instruments (INAF-OACT,
DOT, BBSO, MDI/SOHO, EIT/SOHO, TRACE). We determined the morphological
and magnetic evolution of NOAA 10407, as well as the velocity fields
associated with its magnetic structures. Within the limits imposed by
the spatial and temporal resolution of the images analyzed, the first
evidence of the active region formation is initially observed in the
transition region and lower corona, and later on (i.e. after about 7
h) in the inner layers, as found in a previous analysis concerning a
long-lived, recurrent active region. The results also indicate that
the AFS formed in the active region shows typical upward motion at
the AFS's tops and downward motion at the footpoints. The velocity
values relevant to the upward motions decrease over the evolution
of the region, similarly to the case of the recurrent active region,
while we notice an increasing trend in the downflow velocity during
the early phases of the time interval analyzed by THEMIS. On the other
hand, the AFS preceding legs show a higher downflow than the following
ones, a result in contrast with that found in the long-lived active
region. The chromospheric area overhanging the sunspot umbra shows an
upward motion of ∼ 2 km s<SUP>-1</SUP>, while that above the pores
shows a downward motion of ~4 km s<SUP>-1</SUP>.
---------------------------------------------------------
Title: Galaxy Formation and Cosmic-Ray Acceleration in a Magnetized
Universe
Authors: Vlahos, Loukas; Tsagas, Christos G.; Papadopoulos, Demetrios
2005ApJ...629L...9V Altcode: 2005astro.ph..6742V
We study the linear magnetohydrodynamic behavior of a Newtonian
cosmology with a viscous magnetized fluid of finite conductivity and
generalize the Jeans instability criterion. The presence of the field
favors the anisotropic collapse of the fluid, which in turn leads
to further magnetic amplification and to enhanced current-sheet
formation in the plane normal to the ambient magnetic field. When
the currents exceed a certain threshold, the resulting electrostatic
turbulence can dramatically amplify the resistivity of the medium
(anomalous resistivity). This could trigger strong electric fields and
subsequently the acceleration of ultra-high-energy cosmic rays during
the formation of protogalactic structures.
---------------------------------------------------------
Title: Quiet time particle acceleration in interplanetary space
Authors: Lepreti, F.; Isliker, H.; Petraki, K.; Vlahos, L.
2005A&A...432.1049L Altcode: 2004astro.ph.12214L
We propose a model for the acceleration of charged particles in
interplanetary space that appear during quiet time periods, that is, not
associated with solar activity events like intense flares or coronal
mass ejections. The interaction of charged particles with modeled
turbulent electromagnetic fields, which mimic the fields observed in the
interplanetary medium, is studied. The turbulence is modeled by means
of a dynamical system, the Gledzer-Ohkitani-Yamada (GOY) shell model,
which describes the gross features of the Navier-Stokes equations. The
GOY model is used to build a 3D velocity field, which in turn is used
to numerically solve the ideal magneto-hydrodynamic (MHD) induction
equation, while the electric field is calculated from the ideal Ohm's
law. Particle acceleration in such an environment is investigated by
test particle simulations, and the resulting energy distributions are
discussed and compared to observations of suprathermal electrons and
ions during quiet periods in interplanetary space.
---------------------------------------------------------
Title: Statistical Properties of Dissipative MHD Accelerators
Authors: Arzner, Kaspar; Vlahos, Loukas; Knaepen, Bernard; Denewet,
Nicolas
2005astro.ph..3147A Altcode:
We use exact orbit integration to investigate particle acceleration in
a Gauss field proxy of magnetohydrodynamic (MHD) turbulence. Regions
where the electric current exceeds a critical threshold are declared
to be `dissipative' and endowed with super-Dreicer electric field
${\bf E}_\Omega = \eta {\bf j}$. In this environment, test particles
(electrons) are traced and their acceleration to relativistic energies
is studied. As a main result we find that acceleration mostly takes
place within the dissipation regions, and that the momentum increments
have heavy (non-Gaussian) tails, while the waiting times between
the dissipation regions are approximately exponentially distributed
with intensity proportional to the particle velocity. No correlation
between the momentum increment and the momentum itself is found. Our
numerical results suggest an acceleration scenario with ballistic
transport between independent `black box' accelerators.
---------------------------------------------------------
Title: Particle Acceleration in Stressed Coronal Magnetic Fields
Authors: Turkmani, R.; Vlahos, L.; Galsgaard, K.; Cargill, P. J.;
Isliker, H.
2005ApJ...620L..59T Altcode:
This Letter presents an analysis of particle acceleration in a
model of the complex magnetic field environment in the flaring solar
corona. A slender flux tube, initially in hydrodynamic equilibrium,
is stressed by random photospheric motions. A three-dimensional
MHD code is used to follow the stochastic development of transient
current sheets. These processes generate a highly fragmented electric
field, through which particles are tracked using a relativistic test
particle code. It is shown that both ions and electrons are accelerated
readily to relativistic energies in times of order 10<SUP>-2</SUP>
s for electrons and 10<SUP>-1</SUP> s for protons forming power-law
distributions in energy.
---------------------------------------------------------
Title: Electron acceleration and radiation in evolving complex
active regions
Authors: Anastasiadis, A.; Gontikakis, C.; Vilmer, N.; Vlahos, L.
2004A&A...422..323A Altcode:
We present a model for the acceleration and radiation of solar
energetic particles (electrons) in evolving complex active regions. The
spatio - temporal evolution of active regions is calculated using a
cellular automaton model, based on self-organized criticality. The
acceleration of electrons is due to the presence of randomly placed,
localized electric fields produced by the energy release process,
simulated by the cellular automaton model. We calculate the resulting
kinetic energy distributions of the particles and their emitted X-ray
radiation spectra using the thick target approximation, and we perform a
parametric study with respect to number of electric fields present and
thermal temperature of the injected distribution. Finally, comparing
our results with the existing observations, we find that they are in
a good agreement with the observed X-ray spectra in the energy range
100-1000 keV.
---------------------------------------------------------
Title: On the distribution of magnetic energy storage in solar
active regions
Authors: Fragos, T.; Rantsiou, E.; Vlahos, L.
2004A&A...420..719F Altcode:
A two-dimensional probabilistic Cellular Automaton is used to model
the appearance of active regions at the solar surface. We assume that
two main competing processes control the magnetic field evolution
at the solar surface (1) the magnetic field is locally enhanced by
the flux emergence and/or the coalescence of emerged magnetic flux
and (2) it is diminished by flux cancellation or diffusion. The flux
emergence follows a basic percolation rule; it is more probable at the
points were magnetic flux already exists. The magnetic field is also
enhanced when magnetic fields of the same polarity collide. The flux
cancellation is due either to the gradual diffusion of the magnetic
field, when it is isolated, or to the partial release of energy when
opposite magnetic field lines collide. The percolation model proposed
in this article is capable of reproducing the statistical properties
of the evolving active regions. The evolving simulated magnetograms,
derived from our model, are used to estimate the 3-D magnetic fields
above the photosphere using constant α force-free extrapolation
techniques. Based on the above analysis we are able to estimate a
variety of observed statistical characteristics, e.g. the size and flux
distribution of the magnetic fields at the solar surface, the fractal
dimension of the magnetic structures formed at the photosphere, the
energy release frequency distribution, the waiting time distribution
of the sporadic energy releases and the statistical properties of the
steep horizontal magnetic field gradients in the extrapolated coronal
magnetic field. Our main conclusion is that the photospheric driver
plays a crucial role in the observed flare statistics, and the solar
magnetograms, when interpreted properly, carry important statistical
information for the solar coronal activity (coronal heating, flares,
CME etc.).
---------------------------------------------------------
Title: Particle Acceleration in an Evolving Network of Unstable
Current Sheets
Authors: Vlahos, Loukas; Isliker, Heinz; Lepreti, Fabio
2004ApJ...608..540V Altcode: 2004astro.ph..2645V
We study the acceleration of electrons and protons interacting with
localized, multiple, small-scale dissipation regions inside an evolving,
turbulent active region. The dissipation regions are unstable current
sheets (UCSs), and in their ensemble they form a complex, fractal,
evolving network of acceleration centers. Acceleration and energy
dissipation are thus assumed to be fragmented. A large-scale magnetic
topology provides the connectivity between the UCSs and in this way
determines the degree of possible multiple acceleration. The particles
travel along the magnetic field freely without losing or gaining energy
until they reach a UCS. In a UCS, a variety of acceleration mechanisms
are active, with the end result that the particles depart with a new
momentum. The stochastic acceleration process is represented in the
form of continuous-time random walk, which allows one to estimate the
evolution of the energy distribution of the particles. It is found
that under certain conditions, electrons are heated and accelerated to
energies above 1 MeV in much less than 1 s. Hard X-ray and microwave
spectra are calculated from the electrons' energy distributions, and
they are found to be compatible with the observations. Ions (protons)
are also heated and accelerated, reaching energies up to 10 MeV almost
simultaneously with the electrons. The diffusion of the particles inside
the active region is extremely fast (anomalous superdiffusion). Although
our approach does not provide insight into the details of the specific
acceleration mechanisms involved, its benefits are that it relates
acceleration to the energy release, it well describes the stochastic
nature of the acceleration process, and it can incorporate the flaring
large-scale magnetic topology, potentially even its temporal evolution.
---------------------------------------------------------
Title: Particle Acceleration in Multiple Dissipation Regions
Authors: Arzner, Kaspar; Vlahos, Loukas
2004ApJ...605L..69A Altcode: 2004astro.ph..2605A
The sharp magnetic discontinuities that naturally appear in solar
magnetic flux tubes driven by turbulent photospheric motions
are associated with intense currents. Parker proposed that
these currents can become unstable to a variety of microscopic
processes, with the net result of dramatically enhanced resistivity
and heating (nano-flares). The electric fields associated
with such “hot spots” are also expected to enhance particle
acceleration. We test this hypothesis by exact relativistic orbit
simulations in strong random phase magnetohydrodynamic turbulence
that is forming localized super-Dreicer Ohm electric fields
(10<SUP>2</SUP><=E<SUB>Ω</SUB>/E<SUB>D</SUB><=10<SUP>5</SUP>)
occurring in 2%-15% of the volume. It is found that these fields
indeed yield a large amplification of acceleration of electrons and
ions and can effectively overcome the injection problem. We suggest in
this article that nanoflare heating will be associated with sporadic
particle acceleration.
---------------------------------------------------------
Title: On the Self-Similarity of Unstable Magnetic Discontinuities
in Solar Active Regions
Authors: Vlahos, Loukas; Georgoulis, Manolis K.
2004ApJ...603L..61V Altcode:
We investigate the statistical properties of possible magnetic
discontinuities in two solar active regions over the course
of several hours. We use linear force-free extrapolations to
calculate the three-dimensional magnetic structure in the active
regions. Magnetic discontinuities are identified using various selection
criteria. Independently of the selection criterion, we identify large
numbers of magnetic discontinuities whose free magnetic energies
and volumes obey well-formed power-law distribution functions. The
power-law indices for the free energies are in the range [-1.6,
-1.35], in remarkable agreement with the power-law indices found in the
occurrence frequencies of solar flare energies. This agreement and the
strong self-similarity of the volumes that are likely to host flares
suggest that the observed statistics of flares may be the natural
outcome of a preexisting spatial self-organization accompanying the
energy fragmentation in solar active regions. We propose a dynamical
picture of flare triggering consistent with recent observations by
reconciling our results with the concepts of percolation theory and
self-organized criticality. These concepts rely on self-organization,
which is expected from the fully turbulent state of the magnetic fields
in the solar atmosphere.
---------------------------------------------------------
Title: Impulsive Electron Acceleration by Gravitational Waves
Authors: Vlahos, Loukas; Voyatzis, George; Papadopoulos, Demetrios
2004ApJ...604..297V Altcode: 2003astro.ph.12151V
We investigate the nonlinear interaction of a strong gravitational
wave with the plasma during the collapse of a massive magnetized
star and subsequent formation of a black hole or during the merging
of neutron star binaries (the central engine). We found that under
certain conditions this coupling may result in an efficient energy-space
diffusion of particles. We suggest that the atmosphere created around
the central engine is filled with three-dimensional magnetic neutral
sheets (magnetic nulls). We demonstrate that the passage of strong
pulses of gravitational waves through the magnetic neutral sheets
accelerates electrons to very high energies. Superposition of many
such short-lived accelerators, embedded inside a turbulent plasma,
may be the source of the observed impulsive short-lived bursts. We
conclude that in several astrophysical events, gravitational pulses
may accelerate the tail of the ambient plasma to very high energies
and become the driver for many types of astrophysical bursts.
---------------------------------------------------------
Title: Energetic Particle Acceleration and Radiation in Evolving
Complex Active Regions
Authors: Anastasiadis, A.; Gontikakis, C.; Vilmer, N.; Vlahos, L.
2004hell.conf...71A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Are Gamma Ray Bursts Driven by Gravitational Waves?
Authors: Vlahos, L.; Voyatzis, G.; Papadopoulos, D.
2004BaltA..13..324V Altcode: 2004OAst...13..324V
We investigate the non-linear interaction of a strong gravitational wave
with the plasma during the collapse of a massive magnetized star to form
a black hole, or during the merging of neutron star binaries. We find
that under certain conditions this coupling may result in an efficient
energy space diffusion of particles. We suggest that the atmosphere
created around the central engine is filled with 3-D magnetic neutral
sheets (magnetic nulls). The passage of strong pulses of gravitational
waves through the magnetic neutral sheets accelerates electrons to
very high energies. We conclude that in several astrophysical events
the gravitational pulses may accelerate the tail of the ambient
plasma to very high energies and become the driver for many types of
astrophysical bursts.
---------------------------------------------------------
Title: Energy Release and Particle Acceleration in Complex Active
Regions
Authors: Vlahos, L.
2004cosp...35.1994V Altcode: 2004cosp.meet.1994V
Photospheric fluid flows and magnetic fields, magnetic energy
release and particle acceleration have been treated so far as separate
issues. In the widely used model the impulsive energy release (flares)
is related to the 3D reconnection in current sheet(s), which are
adjusted to simple magnetic topologies (magnetic loops). MHD turbulence
generated from the reconnecting sheet fill the adjusted loop(s) and
accelerate particles. We will review the strong and weak points of
this scenario and attempt to generalized it, for complex and possibly
more realistic magnetic topologies generated by the extrapolation of
observed photospheric magnetic fields.
---------------------------------------------------------
Title: Particle acceleration and radiation in an evolving active
region based on a Cellular Automaton (CA) model
Authors: Anastasiadis, A.; Gontikakis, C.; Vilmer, N.; Vlahos, L.
2002ESASP.506..265A Altcode: 2002svco.conf..265A; 2002ESPM...10..265A
We present a model for the acceleration and radiation of solar energetic
particles (electrons) in an evolving active region. The spatio-temporal
evolution of the active region is calculated using a Cellular Automaton
(CA) model for the energy release process. The acceleration of particles
is due to the presence of randomly placed, localized electric fields. We
calculate the resulting kinetic energy distributions of the particles
and the emitted radiation by performing a parametric study with respect
to the trapping time of the injected distribution.
---------------------------------------------------------
Title: The extended cellular automaton (X-CA) model for lolar flares
Authors: Isliker, H.; Anastasiadis, A.; Vlahos, L.
2002ESASP.506..641I Altcode: 2002svco.conf..641I; 2002ESPM...10..641I
We have developed a new type of cellular automaton (CA) model, the
extended CA (X-CA), for the study of solar flares. The X-CA model
is consistent with the MHD approach, in contrast to the previously
proposed CA models (classical CAs), it consistently yields all the
relevant physical variables, and it successfully reproduces the
observed distributions of total energy, peak flux, and duration of
solar flares. We present and discuss the relevant plasma processes
and set-up which are implemented by the X-CA model in the framework
of a commonly accepted solar flare scenario.
---------------------------------------------------------
Title: Acceleration and radiation model of solar energetic particles
in an evolving active region
Authors: Anastasiadis, A.; Gontikakis, C.; Vilmer, N.; Vlahos, L.
2002ESASP.505..337A Altcode: 2002solm.conf..337A; 2002IAUCo.188..337A
We present a model for the acceleration and radiation of solar energetic
particles (electrons) in an evolving active region. The spatio-temporal
evolution of the active region is calculated using a Cellular Automaton
(CA) model for the energy release process. The acceleration of particles
is due to the presence of randomly placed, localized electric fields. We
calculate the resulting kinetic energy distributions of the particles
by performing a parametric study with respect to the trapping time
of the injected distribution. Our results show a power law or a power
law with an exponential tail behavior for the resulting kinetic energy
distribution, depending on the maximum trapping time of the injected
particles in the acceleration volume. Finally we calculate the emitted
radiation spectrum from the resulting energy distributions.
---------------------------------------------------------
Title: Statistical properties of the evolution of solar magnetic
fields
Authors: Vlahos, Loukas
2002ESASP.505..105V Altcode: 2002solm.conf..105V; 2002IAUCo.188..105V
We are making an attempt to associate the formation and evolution
of active regions with the heating and flaring of the plasmas in the
solar atmosphere above the active region. The working hypothesis in
our review is that "active regions are open dynamical systems away
from equilibrium, driven by the turbulent convection zone". New
magnetic loops emerge from the convection zone and are subject to
surface diffusion (random motion), which leads to cancellation of
magnetic energy when they collide with magnetic structures of opposite
polarity. In the course of their evolution from birth to disappearance,
active regions reach quickly the stage of Self-Organized Criticality
(SOC), heat the corona by driving nano-flares, micro-flares and
flares. We believe that the statistical properties of the active
regions at the photosphere (size distribution, fractal dimension
etc.) are correlated with the statistical properties of all aspects
of solar activity (Ellerman Bombs, Bright Points, flares, particle
acceleration, etc.). Surprisingly, all these phenomena share one common
characteristic, they are self-similar and their statistical behaviour
follows well defined power laws. This last point reinforces our belief
that the solar atmosphere is coupled, through the magnetic field,
with the convection zone, which drives all the observed activity at
the photosphere, chromosphere, corona and interplanetary space.
---------------------------------------------------------
Title: Statistical Properties of the Energy Release in Emerging and
Evolving Active Regions
Authors: Vlahos, Loukas; Fragos, Tassos; Isliker, Heinz; Georgoulis,
Manolis
2002ApJ...575L..87V Altcode: 2002astro.ph..7340V
The formation and evolution of active regions are inherently complex
phenomena. Magnetic fields generated at the base of the convection zone
follow a chaotic evolution before reaching the solar surface. In this
article, we use a two-dimensional probabilistic cellular automaton
to model the statistical properties of the magnetic patterns formed
on the solar surface and to estimate the magnetic energy released in
the interaction of opposite polarities. We assume that newly emerged
magnetic flux tubes stimulate the emergence of new magnetic flux in
their neighborhood. The flux tubes move randomly on the surface of the
Sun, and they cancel and release their magnetic energy when they collide
with magnetic flux of opposite polarity, or diffuse into the “empty”
photosphere. We assume that cancellation of magnetic flux in collisions
causes “flares” and determine the released energy as the difference in
the square of the magnetic field flux (E~B<SUP>2</SUP>). The statistics
of the simulated flares follow a power-law distribution in energy,
f(E)~E<SUP>-a</SUP>, where a=2.2+/-0.1. The size distribution function
of the simulated active regions exhibits a power-law behavior with index
k~1.93+/-0.08, and the fractal dimension of the magnetized areas on
the simulated solar surface is close to D<SUB>F</SUB>~1.42+/-0.12. Both
quantities, D<SUB>F</SUB> and k, are inside the range of the observed
values.
---------------------------------------------------------
Title: Waves and instabilities in an anisotropic universe
Authors: Papadopoulos, D.; Vlahos, L.; Esposito, F. P.
2002A&A...382....1P Altcode: 2001astro.ph.10455P
The excitation of low frequency plasma waves in an expanding anisotropic
cosmological model that contains a magnetic field frozen into the matter
and pointing in the longitudinal direction is discussed. Using the exact
equations governing finite-amplitude wave propagation in hydromagnetic
media within the framework of the general theory of relativity, we
show that a spectrum of magnetized sound waves will be excited and
form large-scale “damped oscillations” in the expanding universe. The
characteristic frequency of the excited waves is slightly shifted away
from the sound frequency and the shift depends on the strength of the
primordial magnetic field. This magnetic field dependent shift may
have an effect on the acoustic peaks of the CMB.
---------------------------------------------------------
Title: MHD consistent cellular automata (CA) models. II. Applications
to solar flares
Authors: Isliker, H.; Anastasiadis, A.; Vlahos, L.
2001A&A...377.1068I Altcode: 2001astro.ph..8365I
In Isliker et al. (\cite{Isliker00b}), an extended cellular automaton
(X-CA) model for solar flares was introduced. In this model, the
interpretation of the model's grid-variable is specified, and the
magnetic field, the current, and an approximation to the electric field
are yielded, all in a way that is consistent with Maxwell's and the
MHD equations. The model also reproduces the observed distributions of
total energy, peak-flux, and durations. Here, we reveal which relevant
plasma physical processes are implemented by the X-CA model and in what
form, and what global physical set-up is assumed by this model when it
is in its natural state (self-organized criticality, SOC). The basic
results are: (1) On large-scales, all variables show characteristic
quasi-symmetries: the current has everywhere a preferential direction,
the magnetic field exhibits a quasi-cylindrical symmetry. (2) The
global magnetic topology forms either (i) closed magnetic field lines
around and along a more or less straight neutral line for the model in
its standard form, or (ii) an arcade of field lines above the bottom
plane and centered along a neutral line, if the model is slightly
modified. (3) In case of the magnetic topology (ii), loading can
be interpreted as if there were a plasma which flows predominantly
upwards, whereas in case of the magnetic topology (i), as if there
were a plasma flow expanding from the neutral line. (4) The small-scale
physics in the bursting phase represent localized diffusive processes,
which are triggered when a quantity which is an approximately linear
function of the current exceeds a threshold. (5) The interplay of
loading and bursting in the X-CA model can be interpreted as follows:
the local diffusivity usually has a value which is effectively zero,
and it turns locally to an anomalous value if the mentioned threshold
is exceeded, whereby diffusion dominates the quiet evolution (loading),
until the critical quantity falls below the threshold again. (6) Flares
(avalanches) are accompanied by the appearance of localized, intense
electric fields. A typical example of the spatio-temporal evolution of
the electric field during a flare is presented. (7) In a variant on
the X-CA model, the magnitude of the current is used directly in the
instability criterion, instead of the approximately linear function
of it. First results indicate that the SOC state persists and is only
slightly modified: distributions of the released energy are still
power-laws with slopes comparable to the ones of the non-modified X-CA
model, and the large scale structures, a characteristic of the SOC
state, remain unchanged. (8) The current-dissipation during flares is
spatially fragmented into a large number of dissipative current-surfaces
of varying sizes, which are spread over a considerably large volume,
and which do not exhibit any kind of simple spatial organization as
a whole. These current-surfaces do not grow in the course of time,
they are very short-lived, but they multiply, giving rise to new
dissipative current-surfaces which are spread further around. They show
thus a highly dynamic temporal evolution.\ It follows that the X-CA
model represents an implementation of the flare scenario of Parker
(\cite{Parker93}) in a rather complete way, comprising aspects from
small scale physics to the global physical set-up, making though some
characteristic simplifications which are unavoidable in the frame-work
of a CA.
---------------------------------------------------------
Title: Fast magnetosonic waves driven by gravitational waves
Authors: Papadopoulos, D.; Stergioulas, N.; Vlahos, L.; Kuijpers, J.
2001A&A...377..701P Altcode: 2001astro.ph..7043P
The propagation of a gravitational wave (GW) through a magnetized
plasma is considered. In particular, we study the excitation of
fast magnetosonic waves (MSW) by a gravitational wave, using the
linearized general-relativistic hydromagnetic equations. We derive the
dispersion relation for the plasma, treating the gravitational wave
as a perturbation in a Minkowski background space-time. We show that
the presence of gravitational waves will drive magnetosonic waves in
the plasma and discuss the potential astrophysical implications.
---------------------------------------------------------
Title: The study of solar flares with the extended cellular automaton
(X-CA) model
Authors: Isliker, H.; Anastasiadis, A.; Vlahos, L.
2001hell.confE..39I Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A cellular automaton model for the magnetic activity in
accretion discs
Authors: Pavlidou, V.; Kuijpers, J.; Vlahos, L.; Isliker, H.
2001A&A...372..326P Altcode:
In this paper we attempt, for the first time, to simulate the magnetic
activity of an accretion disc using a probabilistic cellular automaton
model. Our model is based on three free parameters, the probabilities of
spontaneous and stimulated generation of magnetic flux above the surface
of the disc (S<SUB>0</SUB>, and, respectively, P), and the probability
of diffusive disappearance of flux below the surface (D). The model
describes a changing collection of flux tubes which stick out of the
disc and are anchored inside the disc at their foot-points. Magnetic
flux tubes transfer angular momentum outwards at a rate which is
analytically estimated for each single loop. Our model monitors the
dynamic evolution of both the distribution of magnetic loops and the
mass transfer which results from angular momentum transport due to
this distribution. The energy release due to magnetic flaring is also
recorded as a function of time and exhibits temporal fluctuations with
power spectra that depend on the assumed emission-profile of single
flaring loops: (i) for instantaneous emission, the power-spectra
are flat at low frequencies and turn over at high frequencies to a
power-law with index -0.3; (ii) for emission-profiles in the form
of one-sided exponentials, the power-spectra exhibit clear power-law
behaviour with index -1.7. Fluctuations with a power law index between
-1 and -1.7 are observed in many systems undergoing accretion. We found
that our approach allows steady accretion in a disc by the action
of coronal magnetic flux tubes alone. If we express the effective
viscosity caused by coronal loops in the usual Shakura-Sunyaev alpha
parameter of viscosity, we find values which are in good agreement
with observed values.
---------------------------------------------------------
Title: MHD consistent cellular automata (CA) models. I. Basic features
Authors: Isliker, H.; Anastasiadis, A.; Vlahos, L.
2000A&A...363.1134I Altcode: 2001astro.ph..6111I
A set-up is introduced which can be superimposed onto the existing
solar flare cellular automata (CA) models, and which specifies the
interpretation of the model's variables. It extends the CA models,
yielding the magnetic field, the current, and an approximation to the
electric field, in a way that is consistent with Maxwell's and the MHD
equations. Applications to several solar flare CA models during their
natural state (self-organized criticality (SOC)) show, among others,
that (1) the magnetic field exhibits characteristic large-scale
organization over the entire modeled volume; (2) the magnitude of
the current seems spatially dis-organized, with no obvious tendency
towards large-scale structures or even local organization; (3) bursts
occur at sites with increased current, and after a burst the current
is relaxed; (4) by estimating the energy released in individual bursts
with the use of the current as Ohmic dissipation, it turns out that
the power-law distributions of the released energy persist. The CA
models, extended with the set-up, can thus be considered as models for
energy-release through current-dissipation. The concepts of power-law
loading and anisotropic events (bursts) in CA models are generalized
to 3-D vector-field models, and their effect on the magnetic field
topology is demonstrated.
---------------------------------------------------------
Title: Particle-Acceleration and Radiation in the Turbulent Flow of
a Jet
Authors: Manolakou, Konstantina; Anastasiadis, Anastasios; Vlahos,
Loukas
1999ptep.proc..333M Altcode:
We present a numerical model for electron acceleration and radiation
inside the body of an extragalactic jet. We model the jet environment
as a turbulent medium generating non-linear structures (eddies and/or
shocks) through a cascading process. These structures act like in-situ
accelerators for the electrons that are initially injected from the
central engine. Two types of acceleration processes are considered:
second order Fermi-acceleration and shock-drift acceleration,
depending on the velocity of the turbulent eddies encountered. We
study the modulation of the energy distribution of electrons in such an
environment, by incorporating synchrotron radiation losses in the time
intervals between successive interactions of the particles with the
turbulent structures. By performing a parametric study with respect
to the level of turbulent activity and the time intervals between
interactions, we calculate the temporal evolution of the cut-off
frequency of the synchrotron radiation spectrum of the particles and
discuss our results in connection with recent observations.
---------------------------------------------------------
Title: Flare Physics in Accretion Discs
Authors: Pavlidou, V.; Kuijpers, J.; Vlahos, L.; Isliker, H.
1999ESASP.448..859P Altcode: 1999mfsp.conf..859P; 1999ESPM....9..859P
No abstract at ADS
---------------------------------------------------------
Title: Particle-acceleration and radiation in the turbulent flow of
a jet
Authors: Manolakou, K.; Anastasiadis, A.; Vlahos, L.
1999A&A...345..653M Altcode:
We present a numerical model for electron acceleration and radiation
inside the body of an extragalactic jet. We model the jet environment
as a turbulent medium generating non-linear structures (eddies and/or
shocks) through a cascading process. These structures act like in-situ
accelerators for the electrons that are initially injected from the
central engine. Two types of acceleration processes are considered:
second order Fermi-acceleration and shock-drift acceleration,
depending on the velocity of the turbulent eddies encountered. We
study the modulation of the energy distribution of electrons in such an
environment, by incorporating synchrotron radiation losses in the time
intervals between successive interactions of the particles with the
turbulent structures. By performing a parametric study with respect
to the level of turbulent activity and the time intervals between
interactions, we calculate the temporal evolution of the cut-off
frequency of the synchrotron radiation spectrum of the particles and
discuss our results in connection with recent observations.
---------------------------------------------------------
Title: Derivation of Solar Flare Cellular Automata Models from a
Subset of the Magnetohydrodynamic Equations
Authors: Vassiliadis, D.; Anastasiadis, A.; Georgoulis, M.; Vlahos, L.
1998ApJ...509L..53V Altcode:
Cellular automata (CA) models account for the power-law distributions
found for solar flare hard X-ray observations, but their physics
has been unclear. We examine four of these models and show that
their criteria and magnetic field distribution rules can be derived
by discretizing the MHD diffusion equation as obtained from a
simplified Ohm's law. Identifying the discrete MHD with the CA
models leads to an expression for the resistivity as a function
of the current on the flux tube boundary, as may be expected from
current-driven instabilities. Anisotropic CA models correspond to a
nonlinear resistivity η(J), while isotropic ones are associated with
hyperresistivity η(▽<SUP>2</SUP>J). The discrete equations satisfy
the necessary conditions for self-organized criticality (Lu): there
is local conservation of a field (magnetic flux), while the nonlinear
resistivity provides a rapid dissipation and relaxation mechanism. The
approach justifies many features of the CA models that were originally
based on intuition.
---------------------------------------------------------
Title: Variability of the occurrence frequency of solar flares and
the statistical flare
Authors: Georgoulis, Manolis K.; Vlahos, Loukas
1998A&A...336..721G Altcode:
Self-Organised Criticality (SOC), embedded in cellular automata
models, has been so far viewed as an attractive phenomenological
approach for studying the statistical behaviour of flaring activity
in solar active regions. Well-known statistical properties of flares,
like the robust scaling laws seen in the distribution functions of
characteristic parameters of the events, as well as correlations linking
those parameters, are successfully reproduced by SOC models. Recent
observations, however, challenge the flexibility of SOC, as they
reveal a variation of the flaring power-law indices over short-time
activity periods. The initial SOC models, based on a small-amplitude,
constant external driver and isotropic instability criteria, appear
inefficient to predict variable power-law indices. In this paper we
introduce a SOC-type numerical model, with a number of modifications of
the original SOC concept. We show that scaling laws and correlations
between the events' characteristic parameters survive under the
action of a highly variable driver. A variable driver initiates
a variability in the resulting power-law indices. We reproduce
qualitatively and quantitatively the statistics of flaring activity
during the 154-day periodicity. Moreover, small-scale, anisotropic
instability criteria imply the existence of a soft population of
events, with statistical properties analogous to those attributed to
the hypothetical nanoflares. We show that numerous small-scale events
could be the dominant energy release mechanism in cases of quiescent
coronal activity.
---------------------------------------------------------
Title: A stochastic model for solar type III bursts
Authors: Isliker, H.; Vlahos, L.; Benz, A. O.; Raoult, A.
1998A&A...336..371I Altcode:
A stochastic model for type III bursts is introduced, discussed,
and compared to observations. The active region is assumed to be
inhomogeneous, with a large number of emerging magnetic fibers. At
their bases, random energy release events take place, in the course of
which electrons are accelerated, travel along the fibers and eventually
undergo the bump-on-tail instability. In the non-linear regime, the
formed Langmuir waves induce strong turbulence in the ambient plasma,
with secondary electrostatic waves appearing. Wave-wave scattering
finally leads to the emission of transverse electro-magnetic waves at
the fundamental and the harmonic of the local plasma-frequency. The
superposition of the emissions from all the fibers yields a model
spectrogram for type III bursts (flux as a function of frequency
and time). Peak-flux distributions of the model are compared to the
ones of five observations of type III bursts. It turns out that,
in a statistical sense, the model is largely compatible with the
observations: the majority of the observations can be considered
generated by a process which corresponds with the presented model. The
details of the different sub-processes constituting the model play no
decisive role concerning the statistical properties of the generated
spectrograms, to describe them approximately by randomizing the unknown
elements is sufficient. Therewith, the correspondence of the model
with the data is not unique. Likewise, intrinsic shortness of observed
type III events does not allow a strict enough discrimination between
different possible sub-processes of the model through statistical
tests. With that, the conclusion is that the observations are compatible
with a model which assumes (i) a randomly structured active region,
(ii) a flare-particle acceleration-process which is fragmented into a
large number of sub-processes, (iii) a distribution of the accelerated
particles which is a random fraction of the ambient density and of
power-law form with random index, and (iv) the fragmentary acceleration
events to occur randomly in time, i.e. the temporal structure of
type III events to be random, without any correlations between the
individual bursts.
---------------------------------------------------------
Title: Solar flare cellular automata interpreted as discretized
MHD equations
Authors: Isliker, H.; Anastasiadis, A.; Vassiliadis, D.; Vlahos, L.
1998A&A...335.1085I Altcode:
We show that the Cellular Automaton (CA) model for Solar flares of Lu
and Hamilton (1991) can be understood as the solution to a particular
partial differential equation (PDE), which describes diffusion in
a localized region in space if a certain instability threshold is
met, together with a slowly acting source term. This equation is
then compared to the induction equation of MHD, the equation which
governs the energy release process in solar flares. The similarities
and differences are discussed. We make some suggestions how improved
Cellular Automaton models might be constructed on the basis of MHD,
and how physical units can be introduced in the existing respective
Cellular Automaton models. The introduced formalism of recovering
equations from Cellular Automata models is rather general and can be
applied to other situations as well.
---------------------------------------------------------
Title: Competition Model for the Formation and Evolution of Active
Regions
Authors: Mylonas, N.; Vlahos, L.; Kluiving, R.
1998ASPC..155...19M Altcode: 1998sasp.conf...19M
No abstract at ADS
---------------------------------------------------------
Title: Formation of Active Regions: Observations and Theory (Invited
review)
Authors: Vlahos, L.
1998ASPC..155....3V Altcode: 1998sasp.conf....3V
No abstract at ADS
---------------------------------------------------------
Title: Fundamental-Harmonic emission in a fibrous jet
Authors: Delouis, J. M.; Raoult, A.; Vlahos, L.
1998cee..workE..34D Altcode:
We propose a type III emission model in the middle corona including
both fundamental and harmonic radiation from a fibrous medium. We state
that emitted fundamental and harmonic radiation have the intrinsic
polarization corresponding to coronal field conditions, i.e.,close
to 100% for fundamental radiation and close to 0% for harmonic
radiation. The polarisation ratio of the resulting radiation is then
due to the proportion of fundamental emission over total emission. This
allows a new interpretation for spacial and spectral polarization
properties of type III emission. It also gives a new explanation
for Fundamental-Harmonic pairs of type III bursts. The Fundamental
component and the Harmonic component appear as a mix of fundamental
and harmonic radiation in different proportions. In this frame, most
of abnomalous observational properties of Fondamental-Harmonic pairs
(altitudes, frequency ratio, polarization) find a straightforward
explanation. The model fits the polarisation diagrams established by
the statistical study of (Dulk and Suzuki, 1990). This model is also
in agrement with recent interplanetary stereo observations (Hoang
et al.,1998) which show that type III radiation is emitted at both
fundamental and harmonic modes.
---------------------------------------------------------
Title: Electron Acceleration by Random DC Electric Fields
Authors: Anastasiadis, Anastasios; Vlahos, Loukas; Georgoulis,
Manolis K.
1997ApJ...489..367A Altcode:
We present a global model for the acceleration of electrons in the
framework of the statistical flare model of Vlahos et al. In this model,
solar flares are the result of an internal self-organized critical
(SOC) process in a complex, evolving, and highly inhomogeneous active
region. The acceleration of electrons is due to localized DC electric
fields closely related to the energy-release process in the active
region. Our numerical results for the kinetic energy distribution of
accelerated electrons show a power-law or an exponential-law behavior,
depending on the maximum trapping time of the energetic particles
inside the acceleration volume.
---------------------------------------------------------
Title: Variability of the Occurrence Frequency of Solar Flares and
the Statistical Flare
Authors: Georgoulis, M. K.; Vlahos, L.
1997jena.confE..39G Altcode:
Self-Organized Criticality (SOC) embedded in cellular automata
models has been so far acknowledged as an adequate qualitative way
of studying the statistical behaviour of flaring activity in solar
active regions. These models are able of producing robust power
laws featuring the frequency distributions of the events obtained,
which are closely consistent with observations of flares, as well
as much steeper power-law cut-offs, which may indicate the existence
of the presently unobserved nanoflares. SOC models are based on the
substantial concept that active regions are driven dissipative nonlinear
dynamical systems. The role of the external driver is attributed to the
feedback of magnetic flux that is injected to the system through the
photospheric boundary and to the random shuffling of the footpoints
of coronal loops taking place on the upper photosphere. In previous
numerical studies, the driver used was an infinitesimal perturbation
acting on localized magnetic topologies due to which avalanche-type
instabilities were triggered. Furthermore, the resulting power-law
indices were unique. Recent observations, however, have shown that
the scaling indices of flares' frequency distributions are not kept
constant during certain phases of the solar activity, such as the
154-day periodicity. To tackle this problem we investigate the role of
the driver used, by introducing a highly variable driving mechanism. We
show that the variability of the driver induces a respective variability
in the resulting power-law indices. The variability of the indices
can be well represented by a linear dependence between them and
the driver's scaling index for both "nanoflaring" and "flaring"
activity. Furthermore, a first attempt of connecting the driver with
certain statistical properties of active regions is introduced. The
results stand closely in favor of the observations of flaring activity
during the 154-day periodicity.
---------------------------------------------------------
Title: Solar and Heliospheric Plasma Physics
Authors: Simnett, George M.; Alissandrakis, Constantine E.; Vlahos,
Loukas
1997LNP...489.....S Altcode: 1997shpp.conf.....S
This volume brings together theoretical ideas on the plasma physics of
both hot and dense plasmas in the solar atmosphere and similar physics
applied to the tenuous and cooler plasmas found in the heliosphere. It
is complemented by recent observations. Helioseismology covers the
solar interior and the neutrino problem. Solar and stellar activity
cycles are addressed. The dynamics of magnetic flux tubes in the solar
atmosphere and material flows through the chromosphere into the upper
atmosphere are comprehensively reviewed. Energy release processes and
the production of energetic particles are important to understanding
events in the solar atmosphere and to the dynamics of the tenuous
heliosphere. A glimpse of the future is offered by concluding chapters
on new ground-based and space instrumentation.
---------------------------------------------------------
Title: Energy Release in the Solar Corona
Authors: Bastian, Timothy S.; Vlahos, Loukas
1997LNP...483...68B Altcode: 1997cprs.conf...68B
Energy release in the solar corona drives a wide variety of phenomena,
including flares, filament/prominence eruptions, coronal mass ejections,
solar particle events, as well as coronal heating and the solar
wind. The basic physics of these phenomena and their relationship
to each other remains a vigorous area of inquiry. The Working Group
on Energy Release at Mont Evray directed its attention to recent
observational and theoretical developments relevant to flares and
coronal heating. Particular attention was given to the "fragmentation"
of energy release in solar flares and its interpretation; to the
statistics of the flare phenomenon and whether they can be understood in
terms of "driven dissipative systems"; to quasisteady energy release
and the problem of coronal heating; and to recent observations of
flares and related phenomena.
---------------------------------------------------------
Title: Coronal Heating by Nanoflares and the Variability of the
Occurence Frequency in Solar Flares
Authors: Georgoulis, Manolis K.; Vlahos, Loukas
1996ApJ...469L.135G Altcode:
It has been proposed that flares in the solar corona may well be
a result of an internal self-organized critical (SOC) process in
active regions. We have developed a cellular automaton SOC model
that simulates flaring activity extending over an active sub-flaring
background. In the resulting frequency distributions we obtain two
distinct power laws. That of the weaker events is shorter and much
steeper (power law with index ~=-3.26) than that of the intermediate
and large events (power law with index ~=-1.73). The flatter power law
is in close agreement with observations of flares. Weaker events are
responsible for ~=90% of the total magnetic energy released, indicating
a possible connection of nanoflares with coronal heating. Moreover,
certain mechanisms cause the variability of the resulting indices
and may provide answers to the problem of the variability of flares'
occurrence frequency during the solar cycle.
---------------------------------------------------------
Title: Cellular automaton models of solar flare occurence.
Authors: MacKinnon, A. L.; MacPherson, K. P.; Vlahos, L.
1996A&A...310L...9M Altcode:
We describe a class of stochastic cellular automaton models for the
occurence of the solar flares. "Flaring elements" of a deliberately
unspecified nature are supposed to interact. A 1-D version of the
model, capable of analytical description, conflicts in detail with
the observations but indicates the quantitative success of such a
picture. Minimal a priori assumptions are involved. The qualitative
importance of such a model lies in the arbitrary means of communication
between flaring elements.
---------------------------------------------------------
Title: Competetion Model for the Evolution of solar active Regions
Authors: Mylonas, N.; Kluiving, R.; Vlahos, L.; Gergoulis, M.
1996hell.conf...46M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Are Flares the Result of a self-organisation Process in
active Regions?
Authors: Georgoulis, M. K.; Vlahos, L.; Kluiving, R.
1996hell.conf...52G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Acceleration and Transport of energetic Particles inside
an evolving active Region
Authors: Anastasiadis, A.; Vlahos, L.
1996hell.conf...59A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Global Models for the Active Sun and the Statistics of Flares
Authors: Vlahos, L.
1996ASPC...93..355V Altcode: 1996ress.conf..355V
No abstract at ADS
---------------------------------------------------------
Title: Stochastic particle Acceleration in a strongly turbulent Flow
of a Jet
Authors: Manolakou, C.; Anastasiadis, A.; Vlahos, L.
1996hell.conf..445M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The statistical flare.
Authors: Vlahos, L.; Georgoulis, M.; Kluiving, R.; Paschos, P.
1995A&A...299..897V Altcode:
Solar and stellar flares are interpreted so far as an instability
of a large scale magnetic neutral sheet. In this article, however,
we assume that the active region is highly inhomogeneous: a large
number of magnetic loops are simultaneously present interacting
and randomly forming discontinuities in many independent points in
space. These magnetic discontinuities release energy and force weaker
discontinuities in their neighbourhood to release energy as well. This
complex dynamical system releases constantly energy in the form of small
and large scale explosions. Clustering of many discontinuities in the
same area has the effect of larger scale explosions (flares). This
type of flare with spatiotemporal fragmentation and clustering in
small and large scale structures will be called here the statistical
flare. The statistical flare is simulated using avalanche models
originally introduced by Bak et al. (1988). Avalanche models applied
so far to solar flares (Lu & Hamilton 1991) were isotropic (the
field was distributed equally to the closest neighbours of an unstable
point). These models simulate relatively large events (microflares and
flares). Here we introduce a more refined isotropic avalanche model
as well as an anisotropic avalanche model (energy is distributed only
among the unstable point and those neighbours that develop gradients
higher than a critical value). The anisotropic model simulates
better the smaller events (nanoflares): in contrast to the well-known
results of the isotropic model (a power law with index ~-1.8 in the
peak-luminosity distribution), the anisotropic model produces a much
steeper power law with index ~-3.5. Finally, we introduce a mixed model
(a combination of isotropic and anisotropic models) which gives rise
to two distinct power-law regions in the peak-luminosity distribution,
one with index ~-3.5 accounting for the small events, and one with index
~-1.8 accounting for large events. This last model therefore explains
coronal heating as well as flaring. The three models introduced in this
paper show length-scale invariant behaviour. Model-dependent memory
effects are detected in the peak-luminosity time series produced by
these models.
---------------------------------------------------------
Title: Beam fragmentation and type III bursts.
Authors: Vlahos, L.; Raoult, A.
1995A&A...296..844V Altcode:
We re-investigate the problem of electron beam propagation and the
formation of type III bursts, assuming that the corona is inhomogeneous
and the magnetic field is split in small independent fibers. We
start by injecting in each fiber a beam with random characteristics
(beam density, beam energy, etc.) and follow its non linear evolution
during propagation. We add the contribution of N independent beams in
each frequency and form the expected spectrum. We discuss the fine
structure of type III bursts, the decimetric spikes associated with
type III bursts and the formation of groups of type III bursts.
---------------------------------------------------------
Title: Particle acceleration in the heliosphere
Authors: Vlahos, L.
1995HiA....10..307V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Acceleration and Radiation from a Complex Active Region
Authors: Vlahos, L.
1995LNP...444..115V Altcode: 1995cmer.conf..115V
Active regions are treated in this review as a "paradigm" of a complex
dynamical system. Active regions are formed by magnetic fibers escaping
from the turbulent convection zone. Random movements of the feet of the
fibers in the photosphere and emergence of new magnetic flux from the
convection zone are responsible for the formation of neutral sheets
and magnetic discontinuities inside the active region, which are the
sites for magnetic dissipation. A simple model, based on the scenario
of self organised criticality, reproduces many of the known flare
characteristics. The same model is used to provide a large number of
nanoflares, which can heat the corona. We also show that this complex,
inhomogeneous active region, is an efficient accelerator and reproduce
the observed dm spikes and type III bursts.
---------------------------------------------------------
Title: Particle Acceleration in an Evolving Active Region by an
Ensemble of Shock Waves
Authors: Anastasiadis, Anastasios; Vlahos, Loukas
1994ApJ...428..819A Altcode:
We present a model for the acceleration and transport of energetic
particles (electrons and ions) inside an active region. We propose
that the agent for the acceleration is an ensemble of oblique shock
waves, generated inside an evolving and constantly changing active
region. The acceleration is based on the 'shock drift' mechanism, using
the adiabatic treatment. The high-energy particles are losing energy via
Coulomb collisions and radiation. We calculate the energy distribution
of the particles, their acceleration time, and their maximum energy
as a function of the number of shock waves present. The high-energy
particles are transported inside a chaotic magnetic field and are
reflected randomly when they meet a magnetic mirror point. Finally we
compare our numerical results with the observations.
---------------------------------------------------------
Title: Foreword
Authors: van den Oord, Bert; Kuijpers, Jan; Kuperus, Max; Benz, A. O.;
Brown, J. C.; Einaudi, G.; Kuperus, M.; Raadu, M. A.; Trottet, G.;
van den Oord, G. H. J.; Vlahos, L.; Zheleznyakov, V. V.; Wijburg,
Marion; Fletcher, Lyndsay; Volwerk, Martin
1994SSRv...68D..17V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Theory of fragmented energy release in the Sun
Authors: Vlahos, Loukas
1994SSRv...68...39V Altcode:
The magnetic energy released inside an active region is closely related
to its formation and evolution. Following the evolution of a collection
of flux tubes inside the convection zone and above the photosphere we
can show that many nonlinear structures (current sheets, shock waves,
double layers etc.) are formed. We propose in this review that coronal
heating, flares and particle acceleration are due to the interaction of
the plasma with these nonlinear structures. Approaching active regions
as a driven complex dynamical system we can show that several coherent
ensembles of the nonlinear structures will appear spontaneously. The
statistical analysis of these structures is a major problem in solar
physics. We can also show that many observed large scale structures
are the result of the convolution of non-observable fragmentation in
the energy release process.
---------------------------------------------------------
Title: Galactic Dynamics and N-Body Simulations
Authors: Contopoulos, G.; Spyrou, N. K.; Vlahos, L.
1994LNP...433.....C Altcode: 1994gdnb.conf.....C
This book provides an in-depth coverage of modern research on dynamical
systems. The first part discusses stellar dynamics, integrable systems,
the transition to chaos and instabilities in stellar dynamics as well
as the dynamics of spiral galaxies. Models are given and compared
with observations. The second part is devoted to the direct method
of N-body simulations, to gas dynamics simulations and to galaxy
formation. Special care is taken to give to a pedagogical presentation
of the material which makes this a unique text well suited for graduate
courses in astrophysics.
---------------------------------------------------------
Title: Filamentation of magnetic structures and particle acceleration
in solar and stellar flares
Authors: Vlahos, Loukas
1993AdSpR..13i.161V Altcode: 1993AdSpR..13..161V
We review models for the evolution and energy release of active
region magnetic fields. We propose that turbulent photospheric motions
will break the active region magnetic field in small fibers (current
carrying magnetic filaments) and we address the possibility that this
type of magnetic topology may become the host of thousands of neutral
sheets. We have subsequently analyzed the acceleration and transport
of energetic particles in such an environment. Standard techniques
such as stochastic or shock acceleration, E-field acceleration or
coherent acceleration are reviewed on the basis of a “statistical
flare” model, where many explosions are organised (self-organised
when they reach a critical stage or externally driven by emerging flux
or large scale photospheric flows around filaments) to create a flare
(micro-flare or large flare).
---------------------------------------------------------
Title: Particle acceleration by multiple shocks at the hot spots of
extragalatic radio sources
Authors: Anastasiadis, A.; Vlahos, L.
1993A&A...275..427A Altcode:
We present a model for the acceleration of energetic electrons by
an ensemble of oblique shock waves at the hot spots of extended
extragalactic radio sources. The energization of the electrons
is based on the "shock drift" acceleration mechanism, using the
adiabatic treatment, and electrons are subject to synchrotron losses
as they travel between the shock fronts. We calculate numerically the
energy distribution of electrons and the corresponding intensity of
the radiation produced. We compare our results with the analytical
solution of the Fokker-Planck equation. Our numerical and analytical
results agree well with the existing observations.
---------------------------------------------------------
Title: Transport Phenomena in Solar and Stellar Active Regions
Authors: Vlahos, L.
1993sdtp.conf..235V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High Energy Emission from Normal Stars
Authors: Vlahos, L.
1993LNP...418..129V Altcode: 1993ghea.conf..129V
Introduction Energy Flow and Particle Acceleration Basic Concepts
Spontaneous Emission Bremsstrahlung Emission Cyclotron and Synchrotron
Emission Collective Plasma Emission Plasma Radiation Electron Cyclotron
Maser Instability Observations Hard X-Ray Emission Radio Observations
Summary and Conclusions References
---------------------------------------------------------
Title: On the efficiency of electron cyclotron maser instability in
solar flares
Authors: MacKinnon, A.; Vlahos, L.; Vilmer, N.
1992A&A...256..613M Altcode:
We describe a simple model, designed to estimate the efficiency of
the electron cyclotron maser (ECM) instability inside a magnetic
trap. The emphasis in this model is on the energy loss associated
with the formation of the loss cone distribution, rather than on the
microscopic plasma physics. We find that the net radiation efficiency
is low. Repeated mirroring does not greatly enhance the intrinsic
efficiency, because of the energy lost from the corona in precipitating
electrons. In consequence, absorption of ECM radiation is unlikely to
be an important factor in understanding soft X-ray observations.
---------------------------------------------------------
Title: Particle acceleration inside a 'gas' of shock waves
Authors: Anastasiadis, A.; Vlahos, L.
1991A&A...245..271A Altcode:
A process by which shock waves are formed in jet flows or during
supernovae explosions is presented. Particular attention is given to
the short time scale evolution of N-shock wave-particle interaction. It
is found that most of the energy released by the 'thermal' explosions
will return to thermal energy via shock-shock interactions.
---------------------------------------------------------
Title: An injection model for type III/V bursts in solar flares
Authors: Raoult, A.; Mangeney, A.; Vlahos, L.
1990A&A...233..229R Altcode:
A possible interpretation of the injection of electrons and the
correlation of hard X-ray and type III/V radio emission is presented. A
possible model is also presented of the nonlinear excitation of ion
sound fluctations from type III beams and the streaming of low-energy
superthermal electrons inside a turbulent plasma. It is suggested that
the high-energy electron stream, which generates type III bursts and the
spiky X-ray component, excites intense plasma waves which nonlinearly
drive ion density fluctuations. These fluctuations enhance the collision
frequency of the streaming low-energy particles and force them to form
a positive slope. This allows the 30 keV hot plasma to excite plasma
waves in the same frequency range as type III bursts and to generate
type V emission.
---------------------------------------------------------
Title: Energetic Particles in Solar Flares: Observations Modeling
and Acceleration Processes (Extended Abstract)
Authors: Trottet, G.; Vlahos, L.
1990PDHO....7..184T Altcode: 1990dysu.conf..184T; 1990ESPM....6..184T
No abstract at ADS
---------------------------------------------------------
Title: Particle Acceleration in Solar Flares
Authors: Vlahos, Loukas
1989SoPh..121..431V Altcode: 1989IAUCo.104..431V
Particle acceleration during solar flares is a complex process where the
main `actors' (Direct (D.C.) or turbulent electric fields) are hidden
from us. It is easy to construct a successful particle accelertion
model if we are allowed to impose on the flaring region arbitrary
conditions (e.g., strength and scale length of the D.C. or turbulent
electric fields), but then we have not solved the acceleration problem;
we have simply re-defined it. We outline in this review three recent
observations which indicate that the following physical processes may
happen during solar flares: (1) Release of energy in a large number
of microflares; (2) short time-scales; (3) small length scales;
and (4) coherent radiation and acceleration sources. We propose
that these new findings force us to reformulate the acceleration
process inside a flaring active region assuming that a large number of
reconnection sites will burst almost simultaneously. All the well-known
acceleration mechanisms (electric fields, turbulent fields, shock waves,
etc.) reviewed briefly here, can be used in a statistical model where
each particle is gaining energy through its interaction with many
small reconnection sites.
---------------------------------------------------------
Title: Particle acceleration.
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.;
Alissandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.;
Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima,
H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.;
Trottet, G.; Tsuneta, S.; van Hoven, G.
1989epos.conf..127V Altcode:
Contents: 1. Introduction. 2. Phenomena associated with
mildly-relativistic electrons. 3. Phenomena associated with ions and
relativistic electrons in solar flares. 4. Theoretical studies of
particle acceleration. 5. Achievements - outstanding questions.
---------------------------------------------------------
Title: Particle acceleration and plasma heating at collisionless
shocks in solar flares.
Authors: Cargill, P. J.; Vlahos, L.
1989sasf.confP.325C Altcode: 1989IAUCo.104P.325C; 1988sasf.conf..325C
Recent observations suggest that the energy release in solar flares
may occur in many small bursts. If these bursts give rise to plasma
heating, a large number of collisionless shocks will be generated. These
shocks can individually heat plasma and accelerate particles, but the
interaction of particles with many shocks as well as of shocks with
each other can give rise to further heating and acceleration.
---------------------------------------------------------
Title: Dynamics of sub-relativistic electron beams in magnetic traps -
A model for solar N-bursts
Authors: Hillaris, A.; Alissandrakis, C. E.; Vlahos, L.
1988A&A...195..301H Altcode:
The dynamic evolution of mildly relativistic electrons (10 - 100 keV)
injected into a model magnetic trap is studied numerically, using
the drift approximation. Wave-particle interactions are neglected,
since the beam plasma system is shown to be non-linearly decoupled
in the range of parameters used in this study. The results from the
simulation are used to interpret certain observational characteristics
of the N-bursts observed by the Nançay radio spectrograph. N-bursts
are believed to be the first direct radio evidence for mirror effects
in solar magnetic loops.
---------------------------------------------------------
Title: Narrow-bandwidth radiation processes in space and astrophysical
plasmas: a review.
Authors: Vlahos, L.
1988imdk.conf..411V Altcode:
Energetic electrons "injected" or accelerated inside a dipole magnetic
field radiate broad band electromagnetic radiation due to their fast
gyration around the magnetic field (synchrotron emission). It is well
known that trapped particles form two classes of unstable velocity
distributions inside the magnetic trap: (1) a beam velocity distribution
and (2) a loss cone velocity distribution. The author reviews the plasma
radiation signatures from these two velocity distributions inside
strongly magnetised plasmas and shows that a highly polarised narrow
bandwidth signal should be expected from these magnetic traps. Such
narrow bandwidth emission is observed in all known magnetic traps
in space and astrophysical plasmas (e.g. Earth, Jupiter, solar and
stellar atmospheres, pulsars, etc).
---------------------------------------------------------
Title: Collisionless shock formation and the prompt acceleration of
solar flare ions
Authors: Cargill, P. J.; Goodrich, C. C.; Vlahos, L.
1988A&A...189..254C Altcode:
The formation mechanisms of collisionless shocks in solar flare plasmas
are investigated. The priamry flare energy release is assumed to
arise in the coronal portion of a flare loop as many small regions
or 'hot spots' where the plasma beta locally exceeds unity. One
dimensional hybrid numerical simulations show that the expansion of
these 'hot spots' in a direction either perpendicular or oblique to
the ambient magnetic field gives rise to collisionless shocks in a few
Omega(i), where Omega(i) is the local ion cyclotron frequency. For
solar parameters, this is less than 1 second. The local shocks are
then subsequently able to accelerate particles to 10 MeV in less
than 1 second by a combined drift-diffusive process. The formation
mechanism may also give rise to energetic ions of 100 keV in the
shock vicinity. The presence of these energetic ions is due either
to ion heating or ion beam instabilities and they may act as a seed
population for further acceleration. The prompt acceleration of ions
inferred from the Gamma Ray Spectrometer on the Solar Maximum Mission
can thus be explained by this mechanism.
---------------------------------------------------------
Title: Evolution of the Axial Electron Cyclotron Maser Instability,
with Applications to Solar Microwave Spikes
Authors: Vlahos, Loukas; Sprangle, Phillip
1987ApJ...322..463V Altcode:
The nonlinear evolution of cyclotron radiation from streaming and
gyrating electrons in an external magnetic field is analyzed. The
nonlinear dynamics of both the fields and the particles are treated
fully relativistically and self-consistently. The model includes
a background plasma and electrostatic effects. The analytical
and numerical results show that a substantial portion of the beam
particle energy can be converted to electromagnetic wave energy at
frequencies far above the electron cyclotron frequency. In general,
the excited radiation can propagate parallel to the magnetic field
and, hence, escape gyrothermal absorption at higher cyclotron
harmonics. The high-frequency Doppler-shifted cyclotron instability
can have saturation efficiencies far higher than those associated with
well-known instabilities of the electron cyclotron maser type. Although
the analysis is general, the possibility of using this model to explain
the intense radio emission observed from the sun is explored in detail.
---------------------------------------------------------
Title: Electron Cyclotron Harmonic Wave Acceleration
Authors: Karimabadi, H.; Menyuk, C. R.; Sprangle, P.; Vlahos, L.
1987ApJ...316..462K Altcode:
A nonlinear analysis of particle acceleration in a finite bandwidth,
obliquely propagating electromagnetic cyclotron wave is presented. It
has been suggested by Sprangle and Vlahos in 1983 that the narrow
bandwidth cyclotron radiation emitted by the unstable electron
distribution inside a flaring solar loop can accelerate electrons
outside the loop by the interaction of a monochromatic wave propagating
along the ambient magnetic field with the ambient electrons. It is
shown here that electrons gyrating and streaming along a uniform, static
magnetic field can be accelerated by interacting with the fundamental
or second harmonic of a monochromatic, obliquely propagating cyclotron
wave. It is also shown that the acceleration is virtually unchanged when
a wave with finite bandwidth is considered. This acceleration mechanism
can explain the observed high-energy electrons in type III bursts.
---------------------------------------------------------
Title: Electron Cyclotron Maser Emission from Solar Flares
Authors: Vlahos, Loukas
1987SoPh..111..155V Altcode:
Energetic electrons, with energies 10-100 keV, accelerated during
the impulsive phase of solar flares, sometimes encounter increasing
magnetic fields as they stream towards the chromosphere. A consequence
of the conservation of their magnetic moment is that the electrons with
large initial pitch angle will be reflected at different heights from
the atmosphere. Energetic electrons reflected below the transition
zone will lose most of their energy to collisions and will never
return to the corona. Thus, electrons reflected above the transition
zone form a loss-cone velocity distribution which can be unstable to
Electron Cyclotron Maser (ECM). The interaction of quasi-perpendicular
shocks with the ambient coronal plasma will form a `ring' or `hollow
beam' velocity distribution upstream of the shock. `Ring' velocity
distributions are also unstable to the ECM instability. A review of the
recent results on the theory of ECM will be presented. We will focus
our discussion on the questions: (a) What are the characteristics of
the linear growth rate of the ECM during solar flares? (b) How does
the ECM saturate and what is its efficiency? (c) How does the ECM
generated radiation modify the flare environment? Finally we will
review the outstanding questions in the theory of ECM and we will
relate the theoretical predictions to current observations.
---------------------------------------------------------
Title: Phenomena Associated with Ions and Relativistic Electrons
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.;
Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.;
Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima,
H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.;
Trottet, G.; Tsuneta, S.; van Hoven, G.
1986epos.conf.2.30V Altcode: 1986epos.confB..30V
No abstract at ADS
---------------------------------------------------------
Title: Modeling of ion acceleration through drift and diffusion at
interplanetary shocks
Authors: Decker, R. B.; Vlahos, L.
1986JGR....9113349D Altcode:
We describe a test particle simulation designed to study energetic
charged particle acceleration at oblique fast-mode shocks when magnetic
fluctuations exist upstream and downstream of the shock. The technique
consists of integrating along exact particle orbits in a system where
the angle θ<SUB>1</SUB> between the shock normal and mean upstream
magnetic field, the level of magnetic fluctuations, and the energy
of injected particles can assume a range of values. This allows us to
study time-dependent shock acceleration under conditions not amenable
to analytical techniques. To illustrate the capability of the numerical
mode, we consider proton acceleration under conditions appropriate for
interplanetary shocks near 1 AU, including large-amplitude transverse
magentic fluctuations derived from power spectra of both ambient and
shock associated MHD waves. <P />With all other parameters held fixed,
protons injected at θ<SUB>1</SUB>=0° and θ<SUB>1</SUB>=60° shocks
are accelerated from 10 keV to ~100 keV and ~1 MeV, repectively, within
300 gyroperiods by a combination of the shock drift and first-order
Fermi processes. The energy spectrum downstream of the 60° shock
can be fit with two power laws, with spectral exponent γ=1.7 from 10
keV to ~80 keV and γ=2.6 from ~ 80 keV to 800 keV. Results are also
presented for the situation where the variance and upstream extent of
the shock-associated waves at the 60° shock are reduced relative to
the values used at the 0° shock.
---------------------------------------------------------
Title: Mechanisms for Particle Accleration in Flares
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.;
Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.;
Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima,
H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.;
Trottet, G.; Tsuneta, S.; van Hoven, G.
1986epos.conf.2.42V Altcode: 1986epos.confB..42V
No abstract at ADS
---------------------------------------------------------
Title: Phenomena Associated with Mildly Relativistic Electrons
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.;
Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.;
Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima,
H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.;
Trottet, G.; Tsuneta, S.; van Hoven, G.
1986epos.conf..2.2V Altcode: 1986epos.confB...2V
No abstract at ADS
---------------------------------------------------------
Title: Numerical Studies of Particle Acceleration at Turbulent,
Oblique Shocks with an Application to Prompt Ion Acceleration during
Solar Flares
Authors: Decker, R. B.; Vlahos, L.
1986ApJ...306..710D Altcode:
In this paper we address the problem of charged particle acceleration
at oblique, fast-mode collisionless MHD shock waves when magnetic
turbulence exists in the regions upstream and downstream of the
shock. Specifically, we consider how the acceleration rate depends upon
the angle θ<SUB>1</SUB> between the shock normal and the mean upstream
magnetic field. To handle the general situation where θ<SUB>1</SUB>,
the turbulence level, the shock strength, and the energy of injected
particles can assume a range of values, we perform fully relativistic,
test particle simulations that involve integrating along particle
phase space orbits in the shock turbulence system. As an application
of the numerical code, we study proton acceleration at shocks
under conditions appropriate to the lower solar corona to simulate
prompt ion acceleration during solar flares. Particles undergo shock
acceleration through a combination of the shock drift and first-order
Fermi processes. For protons injected at 100 keV and left in the system
for 500 gyroperiods (∼ 7 ms in a 50 G magnetic field) we obtain the
following results: (1) the percentage of protons accelerated above
10 MeV within 7 ms increases with increasing θ<SUB>1</SUB>, from 0%
at θ<SUB>1</SUB> = 0° to a maximum of 9% at θ<SUB>1</SUB>= 60°
(2) the case θ<SUB>1</SUB> = 75° produces the largest, most rapid
energy gains, with ∼1% of the protons accelerated above 50 MeV;
(3) for 45° < θ<SUB>1</SUB> < 75° , a separate proton
population with energies between 100 keV and 10 MeV is produced
during a superfast acceleration phase lasting only ∼ 10 gyroperiods
(∼ 100 μs) after injection; (4) we compare the peak energy reached
at O = 0 and energy spectrum produced at θ<SUB>1</SUB> = 75° with
predictions from theoretical models, and find reasonable agreement,
although discrepancies do exist. We discuss the implications of the
numerical results as they pertain to time constraints and collisional
loss processes during shock acceleration in the solar corona.
---------------------------------------------------------
Title: Timescales for Shock Formation in Collisionless Plasmas
Authors: Cargill, P. J.; Goodrich, C. C.; Vlahos, L.
1986BAAS...18..710C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Nonlinear analysis of a relativistic beam-plasma cyclotron
instability
Authors: Sprangle, P.; Vlahos, L.
1986PhRvA..33.1261S Altcode:
A self-consistent set of nonlinear and relativistic wave-particle
equations are derived for a magnetized beam-plasma system interacting
with electromagnetic cyclotron waves. In particular, the high-frequency
cyclotron mode interacting with a streaming and gyrating electron
beam within a background plasma is considered in some detail. This
interaction mode may possibly find application as a high-power source
of coherent short-wavelength radiation for laboratory devices. The
background plasma, although passive, plays a central role in this
mechanism by modifying the dielectric properties in which the magnetized
electron beam propagates. For a particular choice of the transverse
beam velocity (i.e., the speed of light divided by the relativistic mass
factor), the interaction frequency equals the nonrelativistic electron
cyclotron frequency times the relativistic mass factor. For this choice
of transverse beam velocity the detrimental effects of a longitudinal
beam velocity spread is virtually removed. Power conversion efficiencies
in excess of 18 percent are both analytically calculated and obtained
through numerical simulations of the wave-particle equations. The
quality of the electron beam, degree of energy and pitch angle spread,
and its effect on the beam-plasma cyclotron instability is studied.
---------------------------------------------------------
Title: Particle acceleration.
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.; Murphy, R. J.;
Allisandrakis, C.; Bai, T.; Batchelor, D.; Benz, A. O.; Chupp, E.;
Ellison, D.; Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.; MacKinnon, A.; Nakajima,
H.; Pesses, M.; Pick, M.; Ryan, J.; Schwartz, R. A.; Smith, D. F.;
Trottet, G.; Tsuneta, S.; van Hoven, G.
1986NASCP2439....2V Altcode:
Contents: 1. Introduction. 2. Phenomena associated with
mildly-relativistic electrons: soft and hard X-ray source structure,
location and development, microwave source structure, location and
development, time structures and time delays in radio and hard X-rays,
microwave rich flares, decimetric - metric observations and comparison
with X-ray observations, discussion of models for X-ray and microwave
emission. 3. Phenomena associated with ions and relativistic electrons:
gamma-ray observations, neutron observations, implications of gamma-ray
and neutron observations, interplanetary charged-particle observations,
acceleration mechanisms. 4. Mechanisms for particle acceleration
in flares: particle acceleration in reconnecting magnetic fields,
electron acceleration along the magnetic field with sub-Dreicer electric
fields, lower hybrid waves, Fermi acceleration and MHD turbulence,
shock acceleration, acceleration of electrons by intense radio waves,
preferential acceleration of heavy ions. 5. Achievements - outstanding
questions.
---------------------------------------------------------
Title: Theoretical studies on rapid fluctuations in solar flares.
Authors: Vlahos, Loukas
1986NASCP2449..455V Altcode: 1986rfsf.nasa..455V
Rapid fluctuations in the emission of solar bursts may have many
different origins. In two separate studies (Vlahos, Sharma, and
Papadopulos, 1983, see Abstr. 34.073.209; Vlahos and Rowland, 1984,
see Abstr. 38.073.055) the conditions for rapid fluctuations in solar
flare driven emissions are analysed.
---------------------------------------------------------
Title: Energetic Ion Acceleration at Collisionless Shocks
Authors: Decker, R. B.; Vlahos, L.
1985ICRC....4..166D Altcode: 1985ICRC...19d.166D
An example is presented from a test particle simulation designed to
study ion acceleration at oblique turbulent shocks. For conditions
appropriate at interplanetary shocks near 1 AU, it is found that a
shock with theta<SUB>B</SUB> n = 60 deg is capable of producing an
energy spectrum extending from 10 keV to approx. 1 MeV in approx 1
hour. In this case total energy gains result primarily from several
separate episodes of shock drift acceleration, each of which occurs
when particles are scattered back to the shock by magnetic fluctuations
in the shock vicinity.
---------------------------------------------------------
Title: Prompt acceleration of ions by oblique turbulent shocks in
solar flares.
Authors: Decker, R. B.; Vlahos, L.
1985ICRC....4...10D Altcode: 1985ICRC...19d..10D
Solar flares often accelerate ions and electrons to relativistic
energies. The details of the acceleration process are not well
understood, but until recently the main trend was to divide the
acceleration process into two phases. During the first phase elctrons
and ions are heated and accelerated up to several hundreds of keV
simultaneously with the energy release. These mildly relativistic
electrons interact with the ambient plasma and magnetic fields
and generate hard X-ray and radio radiation. The second phase,
usually delayed from the first by several minutes, is responsible for
accelerating ions and electrons to relativistic energies. Relativistic
electrons and ions interact with the solar atmosphere or escape from
the Sun and generate gamma ray continuum, gamma ray line emission,
neutron emission or are detected in space by spacecraft. In several
flares the second phase is coincident with the start of a type 2 radio
burst that is believed to be the signature of a shock wave. Observations
from the Solar Maximum Mission spacecraft have shown, for the first
time, that several flares accelerate particles to all energies nearly
simultaneously. These results posed a new theoretical problem: How fast
are shocks and magnetohydrodynamic turbulence formed and how quickly
can they accelerate ions to 50 MeV in the lower corona? This problem
is discussed.
---------------------------------------------------------
Title: Electron cyclotron maser instability in the solar corona -
The role of superthermal tails
Authors: Vlahos, L.; Sharma, R. R.
1985ApJ...290..347V Altcode:
The effect of a superthermal component of electrons on the
loss-cone-driven electron cyclotron maser instability is analyzed. It
is found that for a superthermal tail with temperature about 10 KeV,
the first harmonic (X- and O-mode) is suppressed for n(t)/n(r) of about
1 (n/t/ and n/r/ are the densities of superthermal tail and loss-cone
electrons) and the second harmonic (X- and O-modes) is suppressed
for n(t)/n(r) less than about 0.1. A qualitative discussion on the
formation of superthermal tails is presented and it is suggested that
superthermal tails play an important role on the observed or available
power, at microwave frequencies, from the electron cyclotron maser
instability in the solar corona.
---------------------------------------------------------
Title: Return currents in solar flares - Collisionless effects
Authors: Rowland, H. L.; Vlahos, L.
1985A&A...142..219R Altcode:
If the primary, precipitating electrons in a solar flare are unstable to
beam plasma interactions, it is shown that strong Langmuir turbulence
can seriously modify the way in which a return current is carried
by the background plasma. In particular, the return (or reverse)
current will not be carried by the bulk of the electrons, but by a
small number of high velocity electrons. For beam/plasma densities
>10<SUP>-3</SUP>, this can reduce the effects of collisions on the
return current. For higher density beams where the return current could
be unstable to current driven instabilities, the effects of strong
turbulence anomalous resistivity is shown to prevent the appearance
of such instabilities. Again in this regime, how the return current
is carried is determined by the beam generated strong turbulence.
---------------------------------------------------------
Title: The coalescence instability in solar flares
Authors: Tajima, T.; Brunel, F.; Sakai, J. -I.; Vlahos, L.; Kundu,
M. R.
1985IAUS..107..197T Altcode:
The nonlinear coalescence instability of current carrying solar loops
can explain many of the characteristics of the solar flares such as
their impulsive nature, heating and high energy particle acceleration,
amplitude oscillations of electromagnetic and emission as well as the
characteristics of two-dimensional microwave images obtained during
a flare. The plasma compressibility leads to the explosive phase of
loop coalescence and its overshoot results in amplitude oscillations
in temperatures by adiabatic compression and decompression. It is
noted that the presence of strong electric fields and super-Alfvenic
flows during the course of the instability play an important role in
the production of nonthermal particles. A qualitative explanation on
the physical processes taking place during the nonlinear stages of
the instability is given.
---------------------------------------------------------
Title: Shock drift acceleration in the presence of waves
Authors: Decker, R. B.; Vlahos, L.
1985JGR....90...47D Altcode:
Charged particle acceleration via the shock drift mechanism at
quasi-perpendicular shocks has generally been analyzed by assuming
uniform, time-independent conditions at and near the shock. We present
results from a model designed to study how the shock drift mechanism
is modified when wave activity is included in the shock's upstream and
downstream vicinities. The technique involves numerically following
test particle trajectories in the wave-shock system for predefined
wave fields. In order to compare these results with those obtained
in the scatter-free (i.e., nonwave) case, we restricted particles
to a single shock encounter, which is here defined as the period
during which the particle remains within a gyrodiameter of the
shock. As a particular example, we injected ensembles of ions into a
system consisting of a quasi-perpendicular shock moving through the
interplanetary spectrum of ambient Alfvén waves. As compared with a
single encounter in the scatter-free limit, the inclusion of waves (1)
increases particle transmission through the shock, (2) produces broader
energy distributions for reflected and transmitted particles, with
high-energy tails at energies several times the maximum energy obtained
in the scatter-free case and (3) reduces anisotropies, particularly of
reflected particles, but does not eliminate them. Also, for the range
of energies studied, it was found that the approximate invariance of
the magnetic moment for particle interactions with quasi-perpendicular
shocks is no longer valid when waves are present.
---------------------------------------------------------
Title: Collisionless effects on beam-return current systems in
solar flares
Authors: Vlahos, L.; Rowland, H. L.
1985IAUS..107..521V Altcode:
A theoretical study of the beam-return current system (BRCS) in solar
flares shows that the precipitating electrons modify the way in which
the return current (RC) is carried by the background plasma. In
particular it is found that the RC is not carried by the bulk of
the electrons but by a small number of high-velocity electrons. For
beam/plasma densities exceeding approximately 0.001, this can reduce
the effects of collisions and heating by the RC. For higher-density
beams, where the RC could be unstable to current-driven instabilities,
the effects of strong turbulence anomalous resistivity prevent the
appearance of such instabilities. The main conclusion is that the
BRCS is interconnected, and that the beam-generated strong turbulence
determines how the RC is carried.
---------------------------------------------------------
Title: Electron precipitation in solar flares - Collisionless effects
Authors: Vlahos, L.; Rowland, H. L.
1984A&A...139..263V Altcode:
A large fraction of the electrons which are accelerated during the
impulsive phase of solar flares stream towards the chromosphere and
are unstable to the growth of plasma waves. The linear and non-linear
evolution of plasma waves as a function of time is analyzed with the
use of a set of rate equations that follow in time the nonlinearly
coupled system of plasma waves - ion fluctuations. As an outcome
of the fast transfer of wave energy from the beam to the ambient
plasma, non-thermal electron tails are formed which can stabilize the
anomalous Doppler resonance instability that is responsible for the
pitch angle scattering of the beam electrons. The authors estimate the
non-collisional losses of the precipitating electrons and discuss the
observational implications of their results.
---------------------------------------------------------
Title: Predictions of lithium interactions with earth's bow shock
in the presence of wave activity
Authors: Decker, R. B.; Lui, A. T. Y.; Vlahos, L.
1984JGR....89.7331D Altcode:
The results of a test-particle simulation studying the movement
of a lithium tracer ion injected upstream of the bow shock are
reported. Wave activity consists of parallel and antiparallel
propagating Alfven waves characterized by a frequency power spectrum
within a frequency or range of amplitudes defined separately in the
upstream and downstream regions. The results show that even a moderate
level of wave activity can substantially change the results obtained
in the absence of waves. Among the effects observed are: (1) increased
ion transmission; (2) both the average energy gain and spread about
the average are increased for transmitted and reflected particles;
(3) the average final pitch angle for transmitted particles tends to
90 deg, and the spread of reflected particles is reduced; and (4)
the spatial dispersion of the ions on the bow shock after a single
encounter is increased.
---------------------------------------------------------
Title: Comparative study of the loss cone-driven instabilities in
the low solar corona
Authors: Sharma, R. R.; Vlahos, L.
1984ApJ...280..405S Altcode:
A comparative study of the loss cone-driven instabilities in the
low solar corona is undertaken. The instabilities considered are the
electron cyclotron maser, the whistler, and the electrostatic upper
hybrid. It is shown that the first-harmonic extraordinary mode of the
electron cyclotron maser instability is the fastest growing mode for
strong magnetized plasma (the ratio of plasma frequency to cyclotron
frequency being less than 0.35). For values of the ratio between 0.35
and 1.0, the first-harmonic ordinary mode of the electron cyclotron
maser instability dominates the emission. For ratio values greater
than 1.0, no direct electromagnetic radiation is expected since
other instabilities, which do not escape directly, saturate the
electron cyclotron maser (the whistler or the electrostatic upper
hybrid waves). It is also shown that the second-harmonic electron
cyclotron maser emission never grows to an appreciable level. Thus, it
is suggested that the electron cyclotron maser instability can be the
explanation for the escape of the first harmonic from a flaring loop.
---------------------------------------------------------
Title: Dynamic Development of Run-Away Tails in Flares
Authors: Moghaddam-Taaheri, E.; Vlahos, L.; Rowland, H. L.;
Papadopoulos, K.
1984BAAS...16..536M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Particle Acceleration in Flares
Authors: Vlahos, L.
1984BAAS...16..511V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Electron Cyclotron Maser Instability: The Role of Superthermal
Tails
Authors: Sharma, R. R.; Vlahos, L.
1984BAAS...16..536S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Collisionless Effects on Beam/Return Current Systems in Flares
Authors: Rowland, H. L.; Vlahos, L.
1984BAAS...16R.544R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Flare Induced Stimulated Electron Cyclotron Radiation
Authors: Sprangle, P.; Vlahos, L.; Papadopoulos, K.
1984BAAS...16R.524S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Particle acceleration.
Authors: Rosner, R.; Chupp, E. L.; Gloeckler, G.; Gorney, D. J.;
Krimigis, S. M.; Mok, Y.; Ramaty, R.; Swift, D. W.; Vlahos, L.;
Zweibel, E. G.
1984NASRP1120....2R Altcode:
Contents: 1. Introduction. 2. Phenomenology: Solar flares. Acceleration
processes in the interplanetary medium. Magnetospheric and
ionospheric observations. Particle acceleration outside the solar
system. 3. Theoretical particle acceleration mechanisms: Adiabatic
compression, magnetic pumping, and diffusion. Acceleration in
direct electric fields. Stochastic acceleration. Shock particle
acceleration. Coherent wave acceleration. Injection. 4. The remaining
questions.
---------------------------------------------------------
Title: Stochastic three-wave interaction in flaring solar loops
Authors: Vlahos, L.; Sharma, R. R.; Papadopoulos, K.
1983ApJ...275..374V Altcode:
A model is proposed for the dynamic structure of high-frequency
microwave bursts. The dynamic component is attributed to beams of
precipitating electrons which generate electrostatic waves in the
upper hybrid branch. Coherent upconversion of the electrostatic
waves to electromagnetic waves produces an intrinsically stochastic
emission component which is superposed on the gyrosynchrotron continuum
generated by stably trapped electron fluxes. The role of the density and
temperature of the ambient plasma in the wave growth and the transition
of the three wave upconversion to stochastic, despite the stationarity
of the energy source, are discussed in detail. The model appears to
reproduce the observational features for reasonable parameters of the
solar flare plasma.
---------------------------------------------------------
Title: Electron cyclotron wave acceleration outside a flaring loop
Authors: Sprangle, P.; Vlahos, L.
1983ApJ...273L..95S Altcode:
A model for the secondary acceleration of electrons outside a flaring
loop is proposed. The results suggest that the narrow bandwidth
radiation emitted by the unstable electron distribution inside a
flaring loop can become the driver for secondary electron acceleration
outside the loop. It is shown that a system of electrons gyrating
about and streaming along an adiabatically spatially varying, static
magnetic field can be efficiently accelerated to high energies by an
electromagnetic wave propagating along and polarized transverse to
the static magnetic field. The predictions from our model appear to
be in general agreement with existing observations.
---------------------------------------------------------
Title: Solar microwave bursts — A review
Authors: Kundu, M. R.; Vlahos, L.
1982SSRv...32..405K Altcode:
We review the observational and theoretical results on the physics of
microwave bursts that occur in the solar atmosphere. We particularly
emphasize the advances made in burst physics over the last few
years with the great improvement in spatial and time resolution
especially with instruments like the NRAO three element interferometer,
Westerbork Synthesis Radio Telescope and more recently the Very Large
Array (VLA). We review the observations on pre-flare build-up of an
active region at centimeter wavelengths. In particular we discuss
the observations that in addition to the active region undergoing
brightness and polarization changes on time scales of the order
of an hour before a flare, there can be a change of the sense of
polarization of a component of the relevant active region situated
at the same location as the flare, implying the emergence of a flux
of reverse polarity at coronal levels. The intensity distribution
of cm-λ bursts is similar to that of soft X-ray and hard X-ray
bursts. Indeed, it appears that the flaring behavior of the Sun at cm
wavelengths is similar to that of some other cosmic transients such
as flare stars and X-ray bursters. We discuss three distinct phases
in the evolution of cm bursts, namely, impulsive phase, post-burst
phase, and gradual rise and fall. The radiation mechanism for the
impulsive phase of the microwave burst is gyrosynchrotron emission
from mildly relativistic electrons that are accelerated near the
energy release site and spiral in the strong magnetic field in the
low corona. The details of the velocity distribution function of the
energetic electrons and its time evolution are not known. We review
the spectral characteristics for two kinds of velocity distribution,
e.g., Maxwellian and Maxwellian with a power law tail for the energetic
electrons. In the post-burst phase the energetic electrons are gradually
thermalized. The thermal plasma released in the energy release region
as well as the expanded parts of the overheated upper chromosphere
may alter the emission mechanism. Thus, in the post-burst phase,
depending on the average density and temperature of the thermal plasma,
the emission mechanism may change from gyrosynchrotron to collisional
bremsstrahlung from a thermal plasma. The gradual rise and fall (GFR)
burst represents the heating of a flare plasma to temperatures of the
order of 10<SUP>6</SUP> K, in association with a flare or an X-ray
transient following a filament disruption. We discuss the flux density
spectra of centimeter bursts. The great majority of the bursts have a
single spectral maximum, commonly around 6 cm-λ The U-shaped signature
sometimes found in cm-dcm burst spectrum of large bursts is believed
to a be a reflection of only the fact that there are two different
sources of burst radiation, one for cm-λ and the other for dcm-λ,
with different electron energy distributions and different magnetic
fields. Observations of fine structures with temporal resolutionof 10
100 ms in the intensity profiles of cm-λ bursts are described. The
existence of such fine time structures imply brightness temperatures
in burst sources of order 10<SUP>15</SUP> K; their interpretation
in terms of gyrosynchrotron measuring or the coherent interaction
of upper hybrid waves excited by percipitating electron beams in
a flaring loop is discussed. High spatial resolution observations
(a few seconds of arc to ∼ 1″ arc) are discussed, with special
reference to the one- and two-dimensional maps of cm burst sources. The
dominance of one sense of circular polarization in some weak 6 cm
bursts and its interpretation in terms of energetic electrons confined
in an asymmetric magnetic loop is discussed. Two-dimensional snapshot
maps obtained with the VLA show that multi-peak impulsive 6 cm burst
phase radiation originates from several arcades of loops and that the
burst source often occupies a substantial portion of the flaring loop,
and is not confined strictly to the top of the loop. This phenomenon
is interpreted in terms of the trapping of energetic electrons due
to anomalous doppler resonance instability and the characteristic
scale length of the magnetic field variation along the loop. The VLA
observations also indicate that the onset of the impulsive phase of a
6 cm burst can be associated with the appearance of a new system of
loops. The presence of two loop systems with opposite polarities or
a quadrupole field configuration is reminiscent of flare models in
which a current sheet develops in the interface between two closed
loops. We provide an extensive review of the emission and absorption
processes in thermal and non-thermal velocity distributions. Unlike
the thermal plasma where absorption and emission are inter-related
through Kirchoff's law, the radiation emitted from a small population
of non-thermal electrons can be reabsorbed from the same electrons
(self-absorption) or from the background (thermal) electrons through
gyro-resonance absorption, and free-free absorption. We also suggest
that the non-thermal electrons can be unstable and these instabilities
can be the source of very high brightness temperature, fine structure
(∼ 10 ms) pulsations. Finally in the last part of this review we
present several microwave burst models-the magnetic trap model, the
two-component model, thermal model and the flaring loop model and give
a critical discussion of the strength and weakness of these models.
---------------------------------------------------------
Title: A Model for the Simultaneous Release of Hard X-ray and Type
III Bursts
Authors: Vlahos, L.; Sprangle, P.
1982BAAS...14..874V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The importance of plasma effects on electron-cyclotron
maser-emission from flaring loops
Authors: Sharma, R. R.; Vlahos, L.; Papadopoulos, K.
1982A&A...112..377S Altcode:
Electron cyclotron maser instability has been suggested as the cause
of the observed short (10-20 msec), intense (an approximate brightness
temperature of 10 to the 15th K) and up to 100% polarized microwave
solar emission. It is shown that plasma effects and thermal cyclotron
damping, ignored in previous theories, play an important role in
controlling the frequency range of the emission. The radio emission is
suppressed for ratios of the plasma frequency to the cyclotron frequency
smaller than 0.4. An examination of the cyclotron damping, reveals that
the maser action is suppressed unless a large fraction (i.e., over 10%)
of the accelerated electrons participates in the emission process.
---------------------------------------------------------
Title: Electron acceleration and radiation signatures in loop
coronal transients
Authors: Vlahos, L.; Gergely, T. E.; Papadopoulos, K.
1982ApJ...258..812V Altcode:
It is proposed that in loop coronal transients an erupting loop moves
away from the solar surface, with a velocity exceeding the local Alfven
speed, pushing against the overlying magnetic fields and driving a shock
in the front of the moving part of the loop. Lower hybrid waves are
excited at the shock front and propagate radially toward the center of
the loop with phase velocity along the magnetic field that exceeds the
thermal velocity. The lower hybrid waves stochastically accelerate the
tail of the electron distribution inside the loop. The manner in which
the accelerated electrons are trapped in the moving loop are discussed,
and their radiation signature is estimated. It is suggested that plasma
radiation can explain the power observed in stationary and moving type
IV bursts.
---------------------------------------------------------
Title: Radio imaging of solar flares using the very large array -
New insights into flare process
Authors: Kundu, M. R.; Schmahl, E. J.; Velusamy, T.; Vlahos, L.
1982A&A...108..188K Altcode:
An interpretation of VLA observations of microwave bursts is presented
in an attempt to distinguish between certain models of flares. The VLA
observations provide information about the pre-flare magnetic field
topology and the existence of mildly relativistic electrons accelerated
during flares. Examples are shown of changes in magnetic field topology
in the hour before flares. In one case, new bipolar loops appear to
emerge, which is an essential component of the model developed by
Heyvaerts et al. (1977). In another case, a quadrupole structure,
suggestive of two juxtaposed bipolar loops, appears to trigger the
flare. Because of the observed diversity of magnetic field topologies
in microwave bursts, it is believed that the magnetic energy must
be dissipated in more than one way. The VLA observations are clearly
providing means for sorting out the diverse flare models.
---------------------------------------------------------
Title: Limitation the upconversion of ion sound to langmuir
turbulence.
Authors: Vlahos, L.; Papadopoulos, K.
1982ApJ...252L..75V Altcode:
The weak turbulence theory of Tsytovich, Stenflo and Wilhelmsson
(1981) for evaluation of the nonlinear transfer of ion acoustic waves
to Langmuir waves is shown to be limited in its region of validity
to the level of ion acoustic waves. It is also demonstrated that,
in applying the upconversion of ion sound to Langmuir waves for
electron acceleration, nonlinear scattering should be self-consistently
included, with a suppression of the upconversion process resulting. The
impossibility of accelerating electrons by such a process for any
reasonable physical system is thereby reaffirmed.
---------------------------------------------------------
Title: Radiation signatures from a locally energized flaring loop
Authors: Emslie, A. G.; Vlahos, L.
1980ApJ...242..359E Altcode:
The radiation signatures from a locally energized solar flare loop
based on the physical properties of the energy release mechanisms
were consistent with hard X-ray, microwave, and EUV observations for
plausible source parameters. It was found that a suprathermal tail
of high energy electrons is produced by the primary energy release,
and that the number of energetic charged particles ejected into the
interplanetary medium in the model is consistent with observations. The
radiation signature model predicts that the intrinsic polarization of
the hard X-ray burst should increase over the photon energy range of
20 to 100 keV.
---------------------------------------------------------
Title: Microwave emission from flaring magnetic loops
Authors: Vlahos, L.
1980IAUS...86..173V Altcode:
Characteristics of the microwave emission from a flaring loop are
discussed under the assumptions that (a) the magnetic energy is released
into a small volume compared to the volume of the loop, and the rate at
which magnetic energy is transformed into plasma energy is faster than
the energy losses from the same volume; and (b) the bulk of the energy
released goes into the heating of the plasma and heats primarily the
electrons. A mechanism by which mildly relativistic electrons escape
from the flaring loop to the upper corona is proposed.
---------------------------------------------------------
Title: On the upconversion of ion-sound to Langmuir turbulence
Authors: Vlahos, L.; Papadopoulos, K.
1979ApJ...234L.217V Altcode:
Consideration is given to the upconversion of ion sound waves to
excited Langmuir waves in solar flares. It is shown that, due to
the process of anomalous high-frequency resistivity in which the
reabsorption of Langmuir waves in the presence of ion waves is enhanced,
the upconversion of ion sound waves to Langmuir waves is impossible
in the absence of suprathermal particles and when the electron drift
velocity is less than the electron thermal velocity.
---------------------------------------------------------
Title: Collective plasma effects associated with the continuous
injection model of solar flare particle streams.
Authors: Vlahos, L.; Papadopoulos, K.
1979ApJ...233..717V Altcode:
A modified continuous injection model for impulsive solar flares
that includes self-consistent plasma nonlinearities based on the
concept of marginal stability is presented. A quasi-stationary state
is established, composed of a hot truncated electron Maxwellian
distribution confined by acoustic turbulence on the top of the loop
and energetic electron beams precipitating in the chromosphere. It
is shown that the radiation properties of the model are in accordance
with observations.
---------------------------------------------------------
Title: An interpretation of the polarization structure of microwave
bursts.
Authors: Kundu, M. R.; Vlahos, L.
1979ApJ...232..595K Altcode:
High-spatial-resolution (a few seconds of arc) observations of
microwave bursts have demonstrated that only the impulsive phase of
the burst is polarized; one observes only one polarity in the burst
source if it is weak (Alissandrakis and Kundu) and both polarities if
it is intense (Enome et al.). These results are interpreted in terms
of an asymmetrical bipolar field structure of the loop in which the
energetic electrons responsible for the radiation are contained. The
role of unequal field strengths at the feet of the loop on the number of
electrons trapped and their pitch angle distribution are discussed in
a specific model. Computations of the polarized intensity originating
from each foot of the loop seem to be consistent with the observations
at present available.
---------------------------------------------------------
Title: Plasma properties and radiation signatures of current driven
active region loops on the Sun
Authors: Vlahos, L.
1979PhDT.........2V Altcode:
The average plasma density in the coronal part of a loop is higher than
in its surroundings but the ratio of the plasma kinetic pressure to
magnetic pressure is less than one. These loop-like magnetic field lines
may act as the energy transport lines from the internal layers of the
Sun's photosphere to the chromosphere and the corona where the energy
is stored and suddenly released or slowly dissipated. The photospheric
disturbances which are associated with steady currents along the
potential magnetic field lines were studied in order to identify the
radiation signatures of the current density and its profile as well as
the size of the loop in which the current flows. Three basic phenomena
in which the current supposedly plays an important role are examined:
the sudden release of energy in small loop-like structures (flares); the
heating of loops of different sizes by anomalous current dissipation;
and the sudden erosion of large scale loops (coronal transients). It
is concluded that (1) the current driven from the fluid motions in the
photosphere can, under certain conditions, trigger the tearing mode
instability in a finite volume at the top of a small loop which may
result in a sudden local heating and a transient electron acceleration;
(2) the heating of a loop by 'anomalous' dissipation of currents is
not feasible if the currents are driven from the photosphere and (3)
it appears that under certain conditions the current flowing along a
very large loop can force a loop upwards.
---------------------------------------------------------
Title: Plasma Properties and Radiation Signatures of Current Driven
Active Region Loops on the Sun.
Authors: Vlahos, Loukas
1979PhDT........33V Altcode:
Our present understanding of the various phenomena taking place in the
Sun's atmosphere has radically changed over the past few years. Recent
observations, primarily from Skylab, have confirmed the existence
of small scale structures which in turn have put severe constraints
on the homogeneous plain parallel models of the Sun's atmosphere
traditionally used to analyze the observations. It is now generally
accepted that the small scale magnetic fields are responsible for these
structures. Generally speaking, three types of regions can be identified
on the Sun depending on the dominant magnetic field structure, i.e. the
coronal holes, where the magnetic field lines are diffuse, irregular
and weak; and the active regions, which are characterized by strong
closed magnetic field structures. We usually identify as loops the
magnetic field structures connecting opposite magnetic polarities
in the photosphere. The average plasma density in the coronal part
of the loop is higher than in its surroundings but the ratio of the
plasma kinetic pressure to magnetic pressure is less than one. These
loop-like magnetic field lines may act as the energy transport lines
from the internal layers of the Sun's photosphere to the chromosphere
and the corona where the energy is stored and suddenly released or
slowly dissipated. We focus our studies at the photospheric disturbances
which are associated with steady currents along the potential magnetic
field lines. The current density and its profile as well as the size of
the loop in which the current flows have important radiation signatures
which we have tried to identify in our study. We examine three basic
phenomena in which the current supposedly plays an important role: The
sudden release of energy in small loop-like structures (flares), the
heating of loops of different sizes by anomalous current dissipation and
the sudden eruption of large scale loops (coronal transients). Our main
conclusions are the following:. (a) The current driven from the fluid
motions in the photosphere can, under certain conditions, trigger the
tearing mode instability in a finite volume at the top of a small loop
(length L > 10('9) cm). This may result in a sudden local heating and
a transient electron acceleration. We studied the dynamical evolution
of this "explosion" and analyzed its hard x-ray, EUV microwave and
meter wavelength signatures for the impulsive phase (e.g. t < 1-10
sec). We have also investigated the microwave and soft x-ray emission
of a typical flaring loop in the post-burst phase. (b) The heating of
a loop by "anomalous" dissipation of currents is not feasible if the
currents are driven from the photosphere. We showed that low frequency
current -driven instabilities cannot be excited in large steady loops
(L > 10('10) cm). Further, we showed that if the current-driven low
frequency instabilities are excited, several radiation signatures should
be associated with the loop that is heated. (c) It appears that under
certain conditions the current flowing along a very large loop (L >
10('11) cm) can force a loop upwards. We examined the interaction of
the erupting loops with the surrounding magnetic field. We found that
the loop could act as a piston driving and forming a magnetic shock
at the front edge of the loop, if the expansion velocity is larger
than the local Alfven velocity. Electrons are accelerated in the
wake of the shock (e.g. in the interior of the loop) and subsequently
trapped. We studied the dynamic evolution of the accelerated electrons
and their radio signatures. We found that many of the observed radio
bursts associated with coronal transients can easily be explained by
this model.
