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Author name code: pastor-yabar
ADS astronomy entries on 2022-09-14
author:"Pastor Yabar, Adur"
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Title: Quiet-Sun radiative losses: contribution to chromospheric
heating
Authors: Pastor Yabar, Adur; De la Cruz Rodriguez, Jaime
2022cosp...44.2517P Altcode:
Out-of-sunspots solar magnetism is known to host a plethora of
small-scale, highly dynamic, and fast evolving transient magnetic
events whose contribution to the energetic and mass balance of the solar
atmosphere remains to be clarified. A particularly intriguing property
of the solar atmosphere is that it is not in radiative equilibrium,
that is, the amount of energy escaping through radiation from higher
layers is larger than from lower layers. This is a clear indication that
there is a significant energy transport (other than radiation) needed to
explain at least the additional energy loss through radiation in upper
layers. Recently, it has been shown that this excess of energy loss
is not spatially homogeneous but its variability is extreme, namely,
though the average losses measured for the quiet-Sun match historical
values, the spatial analysis of these losses exhibit variations
in the orders of magnitude. One possible approach to shed light
into this problem is to analyze what kind of thermodynamic/magnetic
event (if any) is associated with these increased losses. To do so,
in this contribution we present the inversion of a quiet-Sun area
co-observed with photospheric and chromospheric polarimetry with CRISP
(FeI 6173{\AA} and CaII 8542{\AA}) and spectroscopy in CaII K with
CHROMIS and MgII h&k lines with IRIS. In order to properly handle
the disparate optical systems associated with the usage of different
wavelengths and facilities, we have employed a novel inversion strategy
that handles coupled inversions in NLTE. In this upgrade, different
optical distortions such as the point-spread-function of the telescope
or different spatial sampling at different datasets are considered by
means of linear transformations, not only in the forward modeling but
also during the inversion step. In doing so, it is possible to achieve
a much more accurate inference of the physical parameters. Here we
will show the physical parameter inferences as well as the radiative
losses associated and their possible source.
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Title: Polarimetric characterization of segmented mirrors
Authors: Pastor Yabar, A.; Asensio Ramos, A.; Manso Sainz, R.;
Collados, M.
2022ApOpt..61.4908P Altcode: 2022arXiv220514640P
We study the impact of the loss of axial symmetry around the optical
axis on the polarimetric properties of a telescope with segmented
primary mirror when each segment is present in a different aging
stage. The different oxidation stage of each segment as they are
substituted in time leads to non-negligible crosstalk terms. This
effect is wavelength dependent and it is mainly determined by the
properties of the reflecting material. For an aluminum coating, the
worst polarimetric behavior due to oxidation is found for the blue
part of the visible. Contrarily, dust -- as modeled in this work --
does not significantly change the polarimetric behavior of the optical
system . Depending on the telescope, there might be segment substitution
sequences that strongly attenuate this instrumental polarization.
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Title: Inference of electric currents in the solar photosphere
Authors: Pastor Yabar, A.; Borrero, J. M.; Quintero Noda, C.; Ruiz
Cobo, B.
2021A&A...656L..20P Altcode: 2021arXiv211204356P
Context. Despite their importance, routine and direct measurements
of electric currents, j, in the solar atmosphere have generally not
been possible. <BR /> Aims: We aim at demonstrating the capabilities
of a newly developed method for determining electric currents in
the solar photosphere. <BR /> Methods: We employ three-dimensional
radiative magneto-hydrodynamic (MHD) simulations to produce synthetic
Stokes profiles in several spectral lines with a spatial resolution
similar to what the newly operational 4-meter Daniel K. Inouye Solar
Telescope solar telescope should achieve. We apply a newly developed
inversion method of the polarized radiative transfer equation with
magneto-hydrostatic (MHS) constraints to infer the magnetic field
vector in the three-dimensional Cartesian domain, B(x, y, z), from the
synthetic Stokes profiles. We then apply Ampere's law to determine
the electric currents, j, from the inferred magnetic field, B(x, y,
z), and compare the results with the electric currents present in
the original MHD simulation. <BR /> Results: We show that the method
employed here is able to attain reasonable reliability (close to 50%
of the cases are within a factor of two, and this increases to 60%-70%
for pixels with B ≥ 300 G) in the inference of electric currents for
low atmospheric heights (optical depths at 500 nm τ<SUB>5</SUB>∈[1,
0.1]) regardless of whether a small or large number of spectral lines
are inverted. Above these photospheric layers, the method's accuracy
strongly deteriorates as magnetic fields become weaker and as the MHS
approximation becomes less accurate. We also find that the inferred
electric currents have a floor value that is related to low-magnetized
plasma, where the uncertainty in the magnetic field inference prevents
a sufficiently accurate determination of the spatial derivatives. <BR />
Conclusions: We present a method that allows the inference of the three
components of the electric current vector at deep atmospheric layers
(photospheric layers) from spectropolarimetric observations.
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Title: Improvement of the Helioseismic and Magnetic Imager (HMI)
Vector Magnetic Field Inversion Code
Authors: Griñón-Marín, Ana Belén; Pastor Yabar, Adur; Liu, Yang;
Hoeksema, J. Todd; Norton, Aimee
2021ApJ...923...84G Altcode: 2021arXiv210909131B; 2021arXiv210909131G
A spectral line inversion code, Very Fast Inversion of the Stokes Vector
(VFISV), has been used since 2010 May to infer the solar atmospheric
parameters from the spectropolarimetric observations taken by the
Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics
Observatory. The magnetic filling factor, the fraction of the surface
with a resolution element occupied by magnetic field, is set to have
a constant value of 1 in the current version of VFISV. This report
describes an improved inversion strategy for the spectropolarimetric
data observed with HMI for magnetic field strengths of intermediate
values in areas spatially not fully resolved. The VFISV inversion code
has been modified to enable inversion of the Stokes profiles with two
different components: one magnetic and one nonmagnetic. In this scheme,
both components share the atmospheric components except for the magnetic
field vector. In order to determine whether the new strategy is useful,
we evaluate the inferred parameters inverted with one magnetic component
(the original version of the HMI inversion) and with two components (the
improved version) using a Bayesian analysis. In pixels with intermediate
magnetic field strengths (e.g., plages), the new version provides
statistically significant values of filling fraction and magnetic
field vector. Not only does the fitting of the Stokes profile improve,
but also the inference of the magnetic parameters and line-of-sight
velocity are obtained uniquely. The new strategy is also proven to
be effective for mitigating the anomalous hemispheric bias in the
east-west magnetic field component in moderate field regions.
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Title: Long-term evolution of three light bridges developed on the
same sunspot
Authors: Griñón-Marín, A. B.; Pastor Yabar, A.; Centeno, R.;
Socas-Navarro, H.
2021A&A...647A.148G Altcode: 2021arXiv210204392B; 2021arXiv210204392G
One important feature of sunspots is the presence of light
bridges. These structures are elongated and bright (as compared
to the umbra) features that seem to be related to the formation
and evolution of sunspots. In this work, we studied the long-term
evolution and the stratification of different atmospheric parameters
of three light bridges formed in the same host sunspot by different
mechanisms. To accomplish this, we used data taken with the GREGOR
Infrared Spectrograph installed at the GREGOR telescope. These data
were inverted to infer the physical parameters of the atmosphere
where the observed spectral profiles were formed of the three light
bridges. We find that, in general, the behaviour of the three light
bridges is typical of this kind of structure with the magnetic
field strength, inclination, and temperature values between the
values at the umbra and the penumbra. We also find that they are of a
significantly non-magnetic character (particularly at the axis of the
light bridges) as it is deduced from the filling factor. In addition,
within the common behaviour of the physical properties of light bridges,
we observe that each one exhibits a particular behaviour. Another
interesting result is that the light bridge cools down, the magnetic
field decreases, and the magnetic field lines get more inclined higher
in the atmosphere. Finally, we studied the magnetic and non-magnetic
line-of-sight velocities of the light bridges. The former shows that
the magnetic component is at rest and, interestingly, its variation
with optical depth shows a bi-modal behaviour. For the line-of-sight
velocity of the non-magnetic component, we see that the core of the
light bridge is at rest or with shallow upflows and clear downflows
sinking through the edges.
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Title: Combining magneto-hydrostatic constraints with Stokes profiles
inversions. II. Application to Hinode/SP observations
Authors: Borrero, J. M.; Pastor Yabar, A.; Ruiz Cobo, B.
2021A&A...647A.190B Altcode: 2021arXiv210104394B
Context. Inversion techniques applied to the radiative transfer equation
for polarized light are capable of inferring the physical parameters in
the solar atmosphere (temperature T, magnetic field B, and line-of-sight
velocity v<SUB>los</SUB>) from observations of the Stokes vector
(i.e., spectropolarimetric observations) in spectral lines. Inferences
are usually performed in the (x, y, τ<SUB>c</SUB>) domain, where
τ<SUB>c</SUB> refers to the optical-depth scale. Generally, their
determination in the (x, y, z) volume is not possible due to the lack
of a reliable estimation of the gas pressure, particularly in regions
of the solar surface harboring strong magnetic fields. <BR /> Aims:
We aim to develop a new inversion code capable of reliably inferring
the physical parameters in the (x, y, z) domain. <BR /> Methods: We
combine, in a self-consistent way, an inverse solver for the radiative
transfer equation (Firtez-DZ) with a solver for the magneto-hydrostatic
equilibrium, which derives realistic values of the gas pressure
by taking the magnetic pressure and tension into account. <BR />
Results: We test the correct behavior of the newly developed code with
spectropolarimetric observations of two sunspots recorded with the
spectropolarimeter (SP) instrument on board the Hinode spacecraft,
and we show how the physical parameters are inferred in the (x, y,
z) domain, with the Wilson depression of the sunspots arising as a
natural consequence of the force balance. In particular, our approach
significantly improves upon previous determinations that were based
on semiempirical models. <BR /> Conclusions: Our results open the door
for the possibility of calculating reliable electric currents in three
dimensions, j(x, y, z), in the solar photosphere. Further consistency
checks would include a comparison with other methods that have recently
been proposed and which achieve similar goals.
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Title: Inference of the chromospheric magnetic field configuration
of solar plage using the Ca II 8542 Å line
Authors: Pietrow, A. G. M.; Kiselman, D.; de la Cruz Rodríguez, J.;
Díaz Baso, C. J.; Pastor Yabar, A.; Yadav, R.
2020A&A...644A..43P Altcode: 2020arXiv200614486P
Context. It has so far proven impossible to reproduce all aspects of
the solar plage chromosphere in quasi-realistic numerical models. The
magnetic field configuration in the lower atmosphere is one of the
few free parameters in such simulations. The literature only offers
proxy-based estimates of the field strength, as it is difficult to
obtain observational constraints in this region. Sufficiently sensitive
spectro-polarimetric measurements require a high signal-to-noise
ratio, spectral resolution, and cadence, which are at the limit
of current capabilities. <BR /> Aims: We use critically sampled
spectro-polarimetric observations of the Ca II 8542 Å line obtained
with the CRISP instrument of the Swedish 1-m Solar Telescope to study
the strength and inclination of the chromospheric magnetic field of
a plage region. This will provide direct physics-based estimates of
these values, which could aid modelers to put constraints on plage
models. <BR /> Methods: We increased the signal-to-noise ratio of the
data by applying several methods including deep learning and PCA. We
estimated the noise level to be 1 × 10<SUP>-3</SUP> I<SUB>c</SUB>. We
then used STiC, a non-local thermodynamic equilibrium inversion
code to infer the atmospheric structure and magnetic field pixel by
pixel. <BR /> Results: We are able to infer the magnetic field strength
and inclination for a plage region and for fibrils in the surrounding
canopy. In the plage we report an absolute field strength of |B| = 440
± 90 G, with an inclination of 10° ±16° with respect to the local
vertical. This value for |B| is roughly double of what was reported
previously, while the inclination matches previous studies done in
the photosphere. In the fibrillar region we found |B| = 300 ± 50 G,
with an inclination of 50° ±13°.
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Title: The dynamics of a solar arch filament system from the
chromosphere to the photosphere
Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.;
Diercke, A.; Collados, M.; Gömöry, P.; Zhong, S.; Hou, Y.; Denker, C.
2020sea..confE.199G Altcode:
We study the dynamics of plasma along the legs of an arch filament
system (AFS) from the chromosphere to the photosphere, observed with
high-cadence spectroscopic data from two ground-based solar telescopes:
the GREGOR telescope (Tenerife) using the GREGOR Infrared Spectrograph
in the He I 10830 Å range and the Swedish Solar Telescope (La Palma)
using the CRisp Imaging Spectro-Polarimeter to observe the Ca II 8542
Å and Fe I 6173 Å spectral lines. The temporal evolution of the
draining of the plasma was followed along the legs of a single arch
filament from the chromosphere to the photosphere. The average Doppler
velocities inferred at the upper chromosphere from the He I 10830 Å
triplet reach velocities up to 20-24 km s<SUP>-1</SUP>, and in the lower
chromosphere and upper photosphere the Doppler velocities reach up to
11 km s<SUP>-1</SUP> and 1.5 km s<SUP>-1</SUP> in the case of the Ca II
8542 Å and Si I 10827 Å spectral lines, respectively. The evolution
of the Doppler velocities at different layers of the solar atmosphere
(chromosphere and upper photosphere) shows that they follow the same
line-of-sight (LOS) velocity patern, which confirms the observational
evidence that the plasma drains toward the photosphere as proposed in
models of AFSs. The observations and the nonlinear force-free field
(NLFFF) extrapolations demonstrate that the magnetic field loops of
the AFS rise with time.
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Title: Discovery of long-period magnetic field oscillations and
motions in isolated sunspots
Authors: Griñón-Marín, A. B.; Pastor Yabar, A.; Socas-Navarro,
H.; Centeno, R.
2020A&A...635A..64G Altcode: 2020arXiv200106030G
We analyse the temporal evolution of the inclination component of
the magnetic field vector for the penumbral area of 25 isolated
sunspots. Compared to previous works, the use of data from the
HMI instrument aboard the SDO observatory facilitates the study
of a very long time series (≈1 week) with a good spatial and
temporal resolution. We used the wavelet technique and we found some
filamentary-shaped events with large wavelet power. Their distribution
of periods is broad, ranging from the lower limit for this study of 48
min up to 63 h. An interesting property of these events is that they
do not appear homogeneously all around the penumbra but they seem to
concentrate at particular locations. The cross-comparison of these
wavelet maps with AIA data shows that the regions where these events
appear are visually related to the coronal loops that connect the outer
penumbra to one or more neighbouring opposite polarity flux patches.
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Title: Photospheric magnetic topology of a north polar region
Authors: Pastor Yabar, A.; Martínez González, M. J.; Collados, M.
2020A&A...635A.210P Altcode: 2020arXiv200304267P
<BR /> Aims: We aim to characterise the magnetism of a large fraction
of the north polar region close to a maximum of activity, when the
polar regions are reversing their dominant polarity. <BR /> Methods:
We make use of full spectropolarimetric data from the CRisp Imaging
Spectro-Polarimeter installed at the Swedish Solar Telescope. The data
consist of a photospheric spectral line, which is used to infer the
various physical parameters of different quiet Sun regions by means
of the solution of the radiative transfer equation. We focus our
analysis on the properties found for the north polar region and their
comparison to the same analysis applied to data taken at disc centre
and low-latitude quiet Sun regions for reference. We also analyse
the spatial distribution of magnetic structures throughout the north
polar region. <BR /> Results: We find that the physical properties
of the polar region (line-of-sight velocity, magnetic flux, magnetic
inclination and magnetic azimuth) are compatible with those found
for the quiet Sun at disc centre and are similar to the ones found
at low latitudes close to the limb. Specifically, the polar region
magnetism presents no specific features. The structures for which
the transformation from a line-of-sight to a local reference frame
was possible harbour large magnetic fluxes (>10<SUP>17</SUP> Mx)
and are in polarity imbalance with a dominant positive polarity, the
largest ones (>10<SUP>19</SUP> Mx) being located below 73° latitude.
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Title: Tracking Downflows from the Chromosphere to the Photosphere
in a Solar Arch Filament System
Authors: González Manrique, Sergio Javier; Kuckein, Christoph;
Pastor Yabar, Adur; Diercke, Andrea; Collados, Manuel; Gömöry,
Peter; Zhong, Sihui; Hou, Yijun; Denker, Carsten
2020ApJ...890...82G Altcode: 2020arXiv200107078G
We study the dynamics of plasma along the legs of an arch filament
system (AFS) from the chromosphere to the photosphere, observed with
high-cadence spectroscopic data from two ground-based solar telescopes:
the GREGOR telescope (Tenerife) using the GREGOR Infrared Spectrograph
in the He I 10830 Å range and the Swedish Solar Telescope (La Palma)
using the CRisp Imaging Spectro-Polarimeter to observe the Ca II 8542
Å and Fe I 6173 Å spectral lines. The temporal evolution of the
draining of the plasma was followed along the legs of a single arch
filament from the chromosphere to the photosphere. The average Doppler
velocities inferred at the upper chromosphere from the He I 10830 Å
triplet reach velocities up to 20-24 km s<SUP>-1</SUP>, and in the lower
chromosphere and upper photosphere the Doppler velocities reach up to
11 km s<SUP>-1</SUP> and 1.5 km s<SUP>-1</SUP> in the case of the Ca II
8542 Å and Si I 10827 Å spectral lines, respectively. The evolution
of the Doppler velocities at different layers of the solar atmosphere
(chromosphere and upper photosphere) shows that they follow the same
line-of-sight (LOS) velocity pattern, which confirms the observational
evidence that the plasma drains toward the photosphere as proposed
in models of AFSs. The Doppler velocity maps inferred from the lower
photospheric Ca I 10839 Å or Fe I 6173 Å spectral lines do not
show the same LOS velocity pattern. Thus, there is no evidence that
the plasma reaches the lower photosphere. The observations and the
nonlinear force-free field (NLFFF) extrapolations demonstrate that
the magnetic field loops of the AFS rise with time. We found flow
asymmetries at different footpoints of the AFS. The NLFFF values of
the magnetic field strength help us to explain these flow asymmetries.
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Title: Combining magnetohydrostatic constraints with Stokes profiles
inversions. I. Role of boundary conditions
Authors: Borrero, J. M.; Pastor Yabar, A.; Rempel, M.; Ruiz Cobo, B.
2019A&A...632A.111B Altcode:
Context. Inversion codes for the polarized radiative transfer
equation, when applied to spectropolarimetric observations (i.e.,
Stokes vector) in spectral lines, can be used to infer the temperature
T, line-of-sight velocity v<SUB>los</SUB>, and magnetic field B as
a function of the continuum optical-depth τ<SUB>c</SUB>. However,
they do not directly provide the gas pressure P<SUB>g</SUB> or density
ρ. In order to obtain these latter parameters, inversion codes rely
instead on the assumption of hydrostatic equilibrium (HE) in addition
to the equation of state (EOS). Unfortunately, the assumption of HE is
rather unrealistic across magnetic field lines, causing estimations
of P<SUB>g</SUB> and ρ to be unreliable. This is because the role
of the Lorentz force, among other factors, is neglected. Unreliable
gas pressure and density also translate into an inaccurate conversion
from optical depth τ<SUB>c</SUB> to geometrical height z. <BR /> Aims:
We aim at improving the determination of the gas pressure and density
via the application of magnetohydrostatic (MHS) equilibrium instead of
HE. <BR /> Methods: We develop a method to solve the momentum equation
under MHS equilibrium (i.e., taking the Lorentz force into account)
in three dimensions. The method is based on the iterative solution of
a Poisson-like equation. Considering the gas pressure P<SUB>g</SUB>
and density ρ from three-dimensional magnetohydrodynamic (MHD)
simulations of sunspots as a benchmark, we compare the results from the
application of HE and MHS equilibrium using boundary conditions with
different degrees of realism. Employing boundary conditions that can
be applied to actual observations, we find that HE retrieves the gas
pressure and density with an error smaller than one order of magnitude
(compared to the MHD values) in only about 47% of the grid points in
the three-dimensional domain. Moreover, the inferred values are within
a factor of two of the MHD values in only about 23% of the domain. This
translates into an error of about 160 - 200 km in the determination of
the z - τ<SUB>c</SUB> conversion (i.e., Wilson depression). On the
other hand, the application of MHS equilibrium with similar boundary
conditions allows determination of P<SUB>g</SUB> and ρ with an error
smaller than an order of magnitude in 84% of the domain. The inferred
values are within a factor of two in more than 55% of the domain. In
this latter case, the z - τ<SUB>c</SUB> conversion is obtained with an
accuracy of 30 - 70 km. Inaccuracies are due in equal part to deviations
from MHS equilibrium and to inaccuracies in the boundary conditions. <BR
/> Results: Compared to HE, our new method, based on MHS equilibrium,
significantly improves the reliability in the determination of the
density, gas pressure, and conversion between geometrical height z and
continuum optical depth τ<SUB>c</SUB>. This method could be used in
conjunction with the inversion of the radiative transfer equation for
polarized light in order to determine the thermodynamic, kinematic,
and magnetic parameters of the solar atmosphere.
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Title: Combining magneto-hydrostatic constraints with Stokes profiles
inversions
Authors: Borrero, J. M.; Pastor Yabar, A.; Rempel, M.; Ruiz Cobo, B.
2019arXiv191014131B Altcode:
Inversion codes for the polarized radiative transfer equation can
be used to infer the temperature $T$, line-of-sight velocity $v_{\rm
los}$, and magnetic field $\rm{\bf B}$ as a function of the continuum
optical-depth $\tau_{\rm c}$. However, they do not directly provide
the gas pressure $P_{\rm g}$ or density $\rho$. In order to obtain
these latter parameters, inversion codes rely instead on the assumption
of hydrostatic equilibrium (HE) in addition to the equation of state
(EOS). Unfortunately, the assumption of HE is rather unrealistic across
magnetic field lines. This is because the role of the Lorentz force,
among other factors, is neglected. This translates into an inaccurate
conversion from optical depth $\tau_{\rm c}$ to geometrical height
$z$. We aim at improving this conversion via the application of
magneto-hydrostatic (MHS) equilibrium instead of HE. We develop a
method to solve the momentum equation under MHS equilibrium (i.e.,
taking the Lorentz force into account) in three dimensions. The method
is based on the solution of a Poisson-like equation. Considering the
gas pressure $P_{\rm g}$ and density $\rho$ from three-dimensional
magneto-hydrodynamic (MHD) simulations of sunspots as a benchmark, we
compare the results from the application of HE and MHS equilibrium. We
find that HE retrieves the gas pressure and density within an order
of magnitude of the MHD values in only about 47 \% of the domain. This
translates into an error of about $160-200$ km in the determination of
the $z-\tau_{\rm c}$ conversion. On the other hand, the application of
MHS equilibrium allows determination of $P_{\rm g}$ and $\rho$ within
an order of magnitude in 84 \% of the domain. In this latter case, the
$z-\tau_{\rm c}$ conversion is obtained with an accuracy of $30-70$ km.
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Title: FIRTEZ-dz. A forward and inverse solver of the polarized
radiative transfer equation under Zeeman regime in geometrical scale
Authors: Pastor Yabar, A.; Borrero, J. M.; Ruiz Cobo, B.
2019A&A...629A..24P Altcode: 2019arXiv190808075P
We present a numerical code that solves the forward and inverse problem
of the polarized radiative transfer equation in geometrical scale under
the Zeeman regime. The code is fully parallelized, making it able to
easily handle large observational and simulated datasets. We checked
the reliability of the forward and inverse modules through different
examples. In particular, we show that even when properly inferring
various physical parameters (temperature, magnetic field components,
and line-of-sight velocity) in optical depth, their reliability in
height-scale depends on the accuracy with which the gas-pressure or
density are known. The code is made publicly available as a tool
to solve the radiative transfer equation and perform the inverse
solution treating each pixel independently. An important feature of
this code, that will be exploited in the future, is that working
in geometrical-scale allows for the direct calculation of spatial
derivatives, which are usually required in order to estimate the gas
pressure and/or density via the momentum equation in a three-dimensional
volume, in particular the three-dimensional Lorenz force.
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Title: Photospheric Magnetic Fields of the Trailing Sunspots in
Active Region NOAA 12396
Authors: Verma, M.; Balthasar, H.; Denker, C.; Böhm, F.; Fischer,
C. E.; Kuckein, C.; González Manrique, S. J.; Sobotka, M.; Bello
González, N.; Diercke, A.; Berkefeld, T.; Collados, M.; Feller, A.;
Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar,
A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K.; Volkmer,
R.; von der Lühe, O.; Waldmann, T.
2019ASPC..526..291V Altcode: 2018arXiv180507752V
The solar magnetic field is responsible for all aspects of solar
activity. Sunspots are the main manifestation of the ensuing solar
activity. Combining high-resolution and synoptic observations has
the ambition to provide a comprehensive description of the sunspot
growth and decay processes. Active region NOAA 12396 emerged on 2015
August 3 and was observed three days later with the 1.5-meter GREGOR
solar telescope on 2015 August 6. High-resolution spectropolarimetric
data from the GREGOR Infrared Spectrograph (GRIS) are obtained in the
photospheric lines Si I λ1082.7 nm and Ca I λ1083.9 nm, together
with the chromospheric He I λ1083.0 nm triplet. These near-infrared
spectropolarimetric observations were complemented by synoptic
line-of-sight magnetograms and continuum images of the Helioseismic
and Magnetic Imager (HMI) and EUV images of the Atmospheric Imaging
Assembly (AIA) on board the Solar Dynamics Observatory (SDO).
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Title: Real-time, multiframe, blind deconvolution of solar images
Authors: Asensio Ramos, A.; de la Cruz Rodríguez, J.; Pastor Yabar, A.
2018A&A...620A..73A Altcode: 2018arXiv180607150A
The quality of images of the Sun obtained from the ground are
severely limited by the perturbing effect of the Earth's turbulent
atmosphere. The post-facto correction of the images to compensate
for the presence of the atmosphere require the combination of
high-order adaptive optics techniques, fast measurements to freeze
the turbulent atmosphere, and very time-consuming blind deconvolution
algorithms. Under mild seeing conditions, blind deconvolution algorithms
can produce images of astonishing quality. They can be very competitive
with those obtained from space, with the huge advantage of the
flexibility of the instrumentation thanks to the direct access to the
telescope. In this contribution we make use of deep learning techniques
to significantly accelerate the blind deconvolution process and produce
corrected images at a peak rate of ∼100 images per second. We present
two different architectures that produce excellent image corrections
with noise suppression while maintaining the photometric properties of
the images. As a consequence, polarimetric signals can be obtained with
standard polarimetric modulation without any significant artifact. With
the expected improvements in computer hardware and algorithms, we
anticipate that on-site real-time correction of solar images will be
possible in the near future.
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Title: Magnetic topology of the north solar pole
Authors: Pastor Yabar, A.; Martínez González, M. J.; Collados, M.
2018A&A...616A..46P Altcode: 2018arXiv180409075P; 2018A&A...616A..46Y
The magnetism at the poles is similar to that of the quiet Sun in the
sense that no active regions are present there. However, the polar quiet
Sun is somewhat different from that at the activity belt as it has a
global polarity that is clearly modulated by the solar cycle. We study
the polar magnetism near an activity maximum when these regions change
their polarity, from which it is expected that its magnetism should be
less affected by the global field. To fully characterise the magnetic
field vector, we use deep full Stokes polarimetric observations of the
15 648.5 and 15 652.8 Å FeI lines. We observe the north pole as well as
a quiet region at disc centre to compare their field distributions. In
order to calibrate the projection effects, we observe an additional
quiet region at the east limb. We find that the two limb datasets share
similar magnetic field vector distributions. This means that close to a
maximum, the poles look like typical limb, quiet-Sun regions. However,
the magnetic field distributions at the limbs are different from the
distribution inferred at disc centre. At the limbs, we infer a new
population of magnetic fields with relatively strong intensities (
600-800 G), inclined by 30° with respect to the line of sight, and
with an azimuth aligned with the solar disc radial direction. This
line-of-sight orientation interpreted as a single magnetic field gives
rise to non-vertical fields in the local reference frame and aligned
towards disc centre. This peculiar topology is very unlikely for such
strong fields according to theoretical considerations. We propose
that this new population at the limbs is due to the observation of
unresolved magnetic loops as seen close to the limb. These loops have
typical granular sizes as measured in the disc centre. At the limbs,
where the spatial resolution decreases, we observe them spatially
unresolved, which explains the new population of magnetic fields that is
inferred. This is the first (indirect) evidence of small-scale magnetic
loops outside the disc centre and would imply that these small-scale
structures are ubiquitous on the entire solar surface. This result has
profound implications for the energetics not only of the photosphere,
but also of the outer layers since these loops have been reported to
reach the chromosphere and the low corona.
---------------------------------------------------------
Title: Dissecting the long-term emission behaviour of the BL Lac
object Mrk 421
Authors: Carnerero, M. I.; Raiteri, C. M.; Villata, M.; Acosta-Pulido,
J. A.; Larionov, V. M.; Smith, P. S.; D'Ammando, F.; Agudo, I.;
Arévalo, M. J.; Bachev, R.; Barnes, J.; Boeva, S.; Bozhilov, V.;
Carosati, D.; Casadio, C.; Chen, W. P.; Damljanovic, G.; Eswaraiah,
E.; Forné, E.; Gantchev, G.; Gómez, J. L.; González-Morales,
P. A.; Griñón-Marín, A. B.; Grishina, T. S.; Holden, M.; Ibryamov,
S.; Joner, M. D.; Jordan, B.; Jorstad, S. G.; Joshi, M.; Kopatskaya,
E. N.; Koptelova, E.; Kurtanidze, O. M.; Kurtanidze, S. O.; Larionova,
E. G.; Larionova, L. V.; Latev, G.; Lázaro, C.; Ligustri, R.; Lin,
H. C.; Marscher, A. P.; Martínez-Lombilla, C.; McBreen, B.; Mihov,
B.; Molina, S. N.; Moody, J. W.; Morozova, D. A.; Nikolashvili, M. G.;
Nilsson, K.; Ovcharov, E.; Pace, C.; Panwar, N.; Pastor Yabar, A.;
Pearson, R. L.; Pinna, F.; Protasio, C.; Rizzi, N.; Redondo-Lorenzo,
F. J.; Rodríguez-Coira, G.; Ros, J. A.; Sadun, A. C.; Savchenko,
S. S.; Semkov, E.; Slavcheva-Mihova, L.; Smith, N.; Strigachev, A.;
Troitskaya, Yu. V.; Troitsky, I. S.; Vasilyev, A. A.; Vince, O.
2017MNRAS.472.3789C Altcode: 2017arXiv170902237C
We report on long-term multiwavelength monitoring of blazar Mrk 421
by the GLAST-AGILE Support Program of the Whole Earth Blazar Telescope
(GASP-WEBT) collaboration and Steward Observatory, and by the Swift and
Fermi satellites. We study the source behaviour in the period 2007-2015,
characterized by several extreme flares. The ratio between the optical,
X-ray and γ-ray fluxes is very variable. The γ-ray flux variations
show a fair correlation with the optical ones starting from 2012. We
analyse spectropolarimetric data and find wavelength-dependence of
the polarization degree (P), which is compatible with the presence of
the host galaxy, and no wavelength dependence of the electric vector
polarization angle (EVPA). Optical polarimetry shows a lack of simple
correlation between P and flux and wide rotations of the EVPA. We build
broad-band spectral energy distributions with simultaneous near-infrared
and optical data from the GASP-WEBT and ultraviolet and X-ray data
from the Swift satellite. They show strong variability in both flux
and X-ray spectral shape and suggest a shift of the synchrotron peak
up to a factor of ∼50 in frequency. The interpretation of the flux
and spectral variability is compatible with jet models including at
least two emitting regions that can change their orientation with
respect to the line of sight.
---------------------------------------------------------
Title: Flows along arch filaments observed in the GRIS `very fast
spectroscopic mode'
Authors: González Manrique, S. J.; Denker, C.; Kuckein, C.; Pastor
Yabar, A.; Collados, M.; Verma, M.; Balthasar, H.; Diercke, A.;
Fischer, C. E.; Gömöry, P.; Bello González, N.; Schlichenmaier,
R.; Cubas Armas, M.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann,
A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Schmidt, D.; Schmidt,
W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude,
J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2017IAUS..327...28G Altcode: 2017arXiv170102206G
A new generation of solar instruments provides improved spectral,
spatial, and temporal resolution, thus facilitating a better
understanding of dynamic processes on the Sun. High-resolution
observations often reveal multiple-component spectral line profiles,
e.g., in the near-infrared He i 10830 Å triplet, which provides
information about the chromospheric velocity and magnetic fine
structure. We observed an emerging flux region, including two small
pores and an arch filament system, on 2015 April 17 with the `very
fast spectroscopic mode' of the GREGOR Infrared Spectrograph (GRIS)
situated at the 1.5-meter GREGOR solar telescope at Observatorio del
Teide, Tenerife, Spain. We discuss this method of obtaining fast (one
per minute) spectral scans of the solar surface and its potential to
follow dynamic processes on the Sun. We demonstrate the performance
of the `very fast spectroscopic mode' by tracking chromospheric
high-velocity features in the arch filament system.
---------------------------------------------------------
Title: Multiwavelength observations of a VHE gamma-ray flare from
PKS 1510-089 in 2015
Authors: Ahnen, M. L.; Ansoldi, S.; Antonelli, L. A.; Arcaro, C.;
Babić, A.; Banerjee, B.; Bangale, P.; Barres de Almeida, U.; Barrio,
J. A.; Bednarek, W.; Bernardini, E.; Berti, A.; Biasuzzi, B.; Biland,
A.; Blanch, O.; Bonnefoy, S.; Bonnoli, G.; Borracci, F.; Bretz,
T.; Carosi, R.; Carosi, A.; Chatterjee, A.; Colin, P.; Colombo, E.;
Contreras, J. L.; Cortina, J.; Covino, S.; Cumani, P.; Da Vela, P.;
Dazzi, F.; De Angelis, A.; De Lotto, B.; de Oña Wilhelmi, E.; Di
Pierro, F.; Doert, M.; Domínguez, A.; Dominis Prester, D.; Dorner,
D.; Doro, M.; Einecke, S.; Eisenacher Glawion, D.; Elsaesser, D.;
Engelkemeier, M.; Fallah Ramazani, V.; Fernández-Barral, A.; Fidalgo,
D.; Fonseca, M. V.; Font, L.; Fruck, C.; Galindo, D.; García López,
R. J.; Garczarczyk, M.; Gaug, M.; Giammaria, P.; Godinović, N.;
Gora, D.; Guberman, D.; Hadasch, D.; Hahn, A.; Hassan, T.; Hayashida,
M.; Herrera, J.; Hose, J.; Hrupec, D.; Hughes, G.; Ishio, K.; Konno,
Y.; Kubo, H.; Kushida, J.; Kuveždić, D.; Lelas, D.; Lindfors, E.;
Lombardi, S.; Longo, F.; López, M.; Majumdar, P.; Makariev, M.;
Maneva, G.; Manganaro, M.; Mannheim, K.; Maraschi, L.; Mariotti,
M.; Martínez, M.; Mazin, D.; Menzel, U.; Mirzoyan, R.; Moralejo,
A.; Moretti, E.; Nakajima, D.; Neustroev, V.; Niedzwiecki, A.; Nievas
Rosillo, M.; Nilsson, K.; Nishijima, K.; Noda, K.; Nogués, L.; Paiano,
S.; Palacio, J.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes,
J. M.; Paredes-Fortuny, X.; Pedaletti, G.; Peresano, M.; Perri, L.;
Persic, M.; Poutanen, J.; Prada Moroni, P. G.; Prandini, E.; Puljak,
I.; Garcia, J. R.; Reichardt, I.; Rhode, W.; Ribó, M.; Rico, J.;
Saito, T.; Satalecka, K.; Schroeder, S.; Schweizer, T.; Shore, S. N.;
Sillanpää, A.; Sitarek, J.; Šnidarić, I.; Sobczynska, D.; Stamerra,
A.; Strzys, M.; Surić, T.; Takalo, L.; Tavecchio, F.; Temnikov, P.;
Terzić, T.; Tescaro, D.; Teshima, M.; Torres, D. F.; Torres-Albà,
N.; Toyama, T.; Treves, A.; Vanzo, G.; Vazquez Acosta, M.; Vovk, I.;
Ward, J. E.; Will, M.; Wu, M. H.; Zarić, D.; Desiante, R.; Becerra
González, J.; D'Ammando, F.; Larsson, S.; Raiteri, C. M.; Reinthal,
R.; Lähteenmäki, A.; Järvelä, E.; Tornikoski, M.; Ramakrishnan,
V.; Jorstad, S. G.; Marscher, A. P.; Bala, V.; MacDonald, N. R.;
Kaur, N.; Sameer; Baliyan, K.; Acosta-Pulido, J. A.; Lazaro, C.;
Martínez-Lombilla, C.; Grinon-Marin, A. B.; Pastor Yabar, A.;
Protasio, C.; Carnerero, M. I.; Jermak, H.; Steele, I. A.; Larionov,
V. M.; Borman, G. A.; Grishina, T. S.
2017A&A...603A..29A Altcode: 2016arXiv161009416M
Context. PKS 1510-089 is one of only a few flat spectrum radio quasars
detected in the very-high-energy (VHE, > 100 GeV) gamma-ray band. <BR
/> Aims: We study the broadband spectral and temporal properties of the
PKS 1510-089 emission during a high gamma-ray state. <BR /> Methods:
We performed VHE gamma-ray observations of PKS 1510-089 with the Major
Atmospheric Gamma Imaging Cherenkov (MAGIC) telescopes during a long,
high gamma-ray state in May 2015. In order to perform broadband modeling
of the source, we have also gathered contemporaneous multiwavelength
data in radio, IR, optical photometry and polarization, UV, X-ray,
and GeV gamma-ray ranges. We construct a broadband spectral energy
distribution (SED) in two periods, selected according to VHE gamma-ray
state. <BR /> Results: PKS 1510-089 was detected by MAGIC during a
few day-long observations performed in the middle of a long, high
optical and gamma-ray state, showing for the first time a significant
VHE gamma-ray variability. Similarly to the optical and gamma-ray
high state of the source detected in 2012, it was accompanied by a
rotation of the optical polarization angle and the emission of a new jet
component observed in radio. However, owing to large uncertainty on the
knot separation time, the association with the VHE gamma-ray emission
cannot be firmly established. The spectral shape in the VHE band during
the flare is similar to those obtained during previous measurements
of the source. The observed flux variability sets constraints for the
first time on the size of the region from which VHE gamma rays are
emitted. We model the broadband SED in the framework of the external
Compton scenario and discuss the possible emission site in view of
multiwavelength data and alternative emission models.
---------------------------------------------------------
Title: Synchrotron emission from the blazar PG 1553+113. An analysis
of its flux and polarization variability
Authors: Raiteri, C. M.; Nicastro, F.; Stamerra, A.; Villata,
M.; Larionov, V. M.; Blinov, D.; Acosta-Pulido, J. A.; Arévalo,
M. J.; Arkharov, A. A.; Bachev, R.; Borman, G. A.; Carnerero, M. I.;
Carosati, D.; Cecconi, M.; Chen, W. -P.; Damljanovic, G.; Di Paola,
A.; Ehgamberdiev, Sh. A.; Frasca, A.; Giroletti, M.; González-Morales,
P. A.; Griñon-Marín, A. B.; Grishina, T. S.; Huang, P. -C.; Ibryamov,
S.; Klimanov, S. A.; Kopatskaya, E. N.; Kurtanidze, O. M.; Kurtanidze,
S. O.; Lähteenmäki, A.; Larionova, E. G.; Larionova, L. V.;
Lázaro, C.; Leto, G.; Liodakis, I.; Martínez-Lombilla, C.; Mihov,
B.; Mirzaqulov, D. O.; Mokrushina, A. A.; Moody, J. W.; Morozova,
D. A.; Nazarov, S. V.; Nikolashvili, M. G.; Ohlert, J. M.; Panopoulou,
G. V.; Pastor Yabar, A.; Pinna, F.; Protasio, C.; Rizzi, N.; Sadun,
A. C.; Savchenko, S. S.; Semkov, E.; Sigua, L. A.; Slavcheva-Mihova,
L.; Strigachev, A.; Tornikoski, M.; Troitskaya, Yu. V.; Troitsky,
I. S.; Vasilyev, A. A.; Vera, R. J. C.; Vince, O.; Zanmar Sanchez, R.
2017MNRAS.466.3762R Altcode: 2016MNRAS.tmp.1569R; 2016arXiv161207000R
In 2015 July 29-September 1, the satellite XMM-Newton pointed at the
BL Lac object PG 1553+133 six times, collecting data for 218 h. During
one of these epochs, simultaneous observations by the Swift satellite
were requested to compare the results of the X-ray and optical-UV
instruments. Optical, near-infrared and radio monitoring was carried out
by the Whole Earth Blazar Telescope (WEBT) collaboration for the whole
observing season. We here present the results of the analysis of all
these data, together with an investigation of the source photometric
and polarimetric behaviour over the last 3 yr. The 2015 EPIC spectra
show slight curvature and the corresponding light curves display fast
X-ray variability with a time-scale of the order of 1 h. In contrast
to previous results, during the brightest X-ray states detected in 2015
the simple log-parabolic model that best fits the XMM-Newton data also
reproduces reasonably well the whole synchrotron bump, suggesting a
peak in the near-UV band. We found evidence of a wide rotation of
the polarization angle in 2014, when the polarization degree was
variable, but the flux remained almost constant. This is difficult
to interpret with deterministic jet emission models, while it can be
easily reproduced by assuming some turbulence of the magnetic field.
---------------------------------------------------------
Title: How to infer the Sun's global magnetic field using the
Hanle effect
Authors: Vieu, T.; Martínez González, M. J.; Pastor Yabar, A.;
Asensio Ramos, A.
2017MNRAS.465.4414V Altcode:
We present a different approach to determine the characteristics
of the global magnetic field of the Sun based on the study of the
Hanle signals. The Hanle effect of a stellar dipole produces a surface
asymmetric pattern of linear polarization that depends on the strength
and geometry of this global field. Moreover, if the dipole is misaligned
with respect to the rotation, the Hanle signals are modulated following
the rotational period. We explore the possibility to retrieve those
characteristics by comparing the computed theoretical signatures with
actual observations. We show that this is possible, in the case of the
Sr I line of the Sun, provided that the polarimetric sensitivity is of
the order or below 10<SUP>-5</SUP>-10<SUP>-6</SUP>. The inference can
be done either using the maps of resolved signals, in particular the
spread of values obtained along different directions on the stellar
disc, or using the disc-integrated signals.
---------------------------------------------------------
Title: Filamentary Oscillations in the Penumbra of Sunspots
Authors: Griñon, Ana Bélen; Pastor Yabar, A.; Socas-Navarro, H.;
Centeno, R.
2017psio.confE.111G Altcode: 2017psio.confE.111A
No abstract at ADS
---------------------------------------------------------
Title: Where are the solar magnetic poles?
Authors: Pastor Yabar, Adur
2017psio.confE..14P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Deep probing of the photospheric sunspot penumbra: no evidence
of field-free gaps
Authors: Borrero, J. M.; Asensio Ramos, A.; Collados, M.;
Schlichenmaier, R.; Balthasar, H.; Franz, M.; Rezaei, R.; Kiess, C.;
Orozco Suárez, D.; Pastor Yabar, A.; Berkefeld, T.; von der Lühe,
O.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Soltau, D.; Volkmer, R.;
Waldmann, T.; Denker, C.; Hofmann, A.; Staude, J.; Strassmeier, K. G.;
Feller, A.; Lagg, A.; Solanki, S. K.; Sobotka, M.; Nicklas, H.
2016A&A...596A...2B Altcode: 2016arXiv160708165B
Context. Some models for the topology of the magnetic field in
sunspot penumbrae predict regions free of magnetic fields or with
only dynamically weak fields in the deep photosphere. <BR /> Aims:
We aim to confirm or refute the existence of weak-field regions in
the deepest photospheric layers of the penumbra. <BR /> Methods:
We investigated the magnetic field at log τ<SUB>5</SUB> = 0 is
by inverting spectropolarimetric data of two different sunspots
located very close to disk center with a spatial resolution of
approximately 0.4-0.45”. The data have been recorded using the GRIS
instrument attached to the 1.5-m solar telescope GREGOR at the El
Teide observatory. The data include three Fe I lines around 1565 nm,
whose sensitivity to the magnetic field peaks half a pressure scale
height deeper than the sensitivity of the widely used Fe I spectral
line pair at 630 nm. Before the inversion, the data were corrected
for the effects of scattered light using a deconvolution method with
several point spread functions. <BR /> Results: At log τ<SUB>5</SUB>
= 0 we find no evidence of regions with dynamically weak (B<
500 Gauss) magnetic fields in sunspot penumbrae. This result is much
more reliable than previous investigations made on Fe I lines at 630
nm. Moreover, the result is independent of the number of nodes employed
in the inversion, is independent of the point spread function used to
deconvolve the data, and does not depend on the amount of stray light
(I.e., wide-angle scattered light) considered.
---------------------------------------------------------
Title: Spectropolarimetric observations of an arch filament system
with the GREGOR solar telescope
Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.;
Kuckein, C.; Kavka, J.; Kučera, A.; Schwartz, P.; Vašková, R.;
Berkefeld, T.; Collados Vera, M.; Denker, C.; Feller, A.; Hofmann,
A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.;
Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1050B Altcode: 2016arXiv160901514B
Arch filament systems occur in active sunspot groups, where a fibril
structure connects areas of opposite magnetic polarity, in contrast to
active region filaments that follow the polarity inversion line. We
used the GREGOR Infrared Spectrograph (GRIS) to obtain the full
Stokes vector in the spectral lines Si I λ1082.7 nm, He I λ1083.0
nm, and Ca I λ1083.9 nm. We focus on the near-infrared calcium line
to investigate the photospheric magnetic field and velocities, and
use the line core intensities and velocities of the helium line to
study the chromospheric plasma. The individual fibrils of the arch
filament system connect the sunspot with patches of magnetic polarity
opposite to that of the spot. These patches do not necessarily coincide
with pores, where the magnetic field is strongest. Instead, areas are
preferred not far from the polarity inversion line. These areas exhibit
photospheric downflows of moderate velocity, but significantly higher
downflows of up to 30 km s<SUP>-1</SUP> in the chromospheric helium
line. Our findings can be explained with new emerging flux where the
matter flows downward along the field lines of rising flux tubes,
in agreement with earlier results.
---------------------------------------------------------
Title: Magnetic fields of opposite polarity in sunspot penumbrae
Authors: Franz, M.; Collados, M.; Bethge, C.; Schlichenmaier, R.;
Borrero, J. M.; Schmidt, W.; Lagg, A.; Solanki, S. K.; Berkefeld,
T.; Kiess, C.; Rezaei, R.; Schmidt, D.; Sigwarth, M.; Soltau, D.;
Volkmer, R.; von der Luhe, O.; Waldmann, T.; Orozco, D.; Pastor Yabar,
A.; Denker, C.; Balthasar, H.; Staude, J.; Hofmann, A.; Strassmeier,
K.; Feller, A.; Nicklas, H.; Kneer, F.; Sobotka, M.
2016A&A...596A...4F Altcode: 2016arXiv160800513F
Context. A significant part of the penumbral magnetic field returns
below the surface in the very deep photosphere. For lines in the
visible, a large portion of this return field can only be detected
indirectly by studying its imprints on strongly asymmetric and
three-lobed Stokes V profiles. Infrared lines probe a narrow layer
in the very deep photosphere, providing the possibility of directly
measuring the orientation of magnetic fields close to the solar
surface. <BR /> Aims: We study the topology of the penumbral magnetic
field in the lower photosphere, focusing on regions where it returns
below the surface. <BR /> Methods: We analyzed 71 spectropolarimetric
datasets from Hinode and from the GREGOR infrared spectrograph. We
inferred the quality and polarimetric accuracy of the infrared data
after applying several reduction steps. Techniques of spectral
inversion and forward synthesis were used to test the detection
algorithm. We compared the morphology and the fractional penumbral
area covered by reversed-polarity and three-lobed Stokes V profiles for
sunspots at disk center. We determined the amount of reversed-polarity
and three-lobed Stokes V profiles in visible and infrared data of
sunspots at various heliocentric angles. From the results, we computed
center-to-limb variation curves, which were interpreted in the context
of existing penumbral models. <BR /> Results: Observations in visible
and near-infrared spectral lines yield a significant difference in the
penumbral area covered by magnetic fields of opposite polarity. In
the infrared, the number of reversed-polarity Stokes V profiles is
smaller by a factor of two than in the visible. For three-lobed Stokes
V profiles the numbers differ by up to an order of magnitude.
---------------------------------------------------------
Title: Horizontal flow fields in and around a small active region. The
transition period between flux emergence and decay
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González
Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke,
A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor
Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert,
M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016A&A...596A...3V Altcode: 2016arXiv160507462V
Context. The solar magnetic field is responsible for all aspects
of solar activity. Thus, emergence of magnetic flux at the surface
is the first manifestation of the ensuing solar activity. <BR />
Aims: Combining high-resolution and synoptic observations aims to
provide a comprehensive description of flux emergence at photospheric
level and of the growth process that eventually leads to a mature
active region. <BR /> Methods: The small active region NOAA 12118
emerged on 2014 July 17 and was observed one day later with the 1.5-m
GREGOR solar telescope on 2014 July 18. High-resolution time-series
of blue continuum and G-band images acquired in the blue imaging
channel (BIC) of the GREGOR Fabry-Pérot Interferometer (GFPI) were
complemented by synoptic line-of-sight magnetograms and continuum
images obtained with the Helioseismic and Magnetic Imager (HMI) onboard
the Solar Dynamics Observatory (SDO). Horizontal proper motions and
horizontal plasma velocities were computed with local correlation
tracking (LCT) and the differential affine velocity estimator (DAVE),
respectively. Morphological image processing was employed to measure
the photometric and magnetic area, magnetic flux, and the separation
profile of the emerging flux region during its evolution. <BR />
Results: The computed growth rates for photometric area, magnetic
area, and magnetic flux are about twice as high as the respective
decay rates. The space-time diagram using HMI magnetograms of five days
provides a comprehensive view of growth and decay. It traces a leaf-like
structure, which is determined by the initial separation of the two
polarities, a rapid expansion phase, a time when the spread stalls,
and a period when the region slowly shrinks again. The separation
rate of 0.26 km s<SUP>-1</SUP> is highest in the initial stage, and
it decreases when the separation comes to a halt. Horizontal plasma
velocities computed at four evolutionary stages indicate a changing
pattern of inflows. In LCT maps we find persistent flow patterns such
as outward motions in the outer part of the two major pores, a diverging
feature near the trailing pore marking the site of upwelling plasma and
flux emergence, and low velocities in the interior of dark pores. We
detected many elongated rapidly expanding granules between the two
major polarities, with dimensions twice as large as the normal granules.
---------------------------------------------------------
Title: Upper chromospheric magnetic field of a sunspot penumbra:
observations of fine structure
Authors: Joshi, J.; Lagg, A.; Solanki, S. K.; Feller, A.; Collados,
M.; Orozco Suárez, D.; Schlichenmaier, R.; Franz, M.; Balthasar,
H.; Denker, C.; Berkefeld, T.; Hofmann, A.; Kiess, C.; Nicklas, H.;
Pastor Yabar, A.; Rezaei, R.; Schmidt, D.; Schmidt, W.; Sobotka, M.;
Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe,
O.; Waldmann, T.
2016A&A...596A...8J Altcode: 2016arXiv160801988J
<BR /> Aims: The fine-structure of the magnetic field in a sunspot
penumbra in the upper chromosphere is to be explored and compared
to that in the photosphere. <BR /> Methods: Spectropolarimetric
observations with high spatial resolution were recorded with the 1.5-m
GREGOR telescope using the GREGOR Infrared Spectrograph (GRIS). The
observed spectral domain includes the upper chromospheric Hei triplet
at 10 830 Å and the photospheric Sii 10 827.1 Å and Cai 10 833.4 Å
spectral lines. The upper chromospheric magnetic field is obtained
by inverting the Hei triplet assuming a Milne-Eddington-type model
atmosphere. A height-dependent inversion was applied to the Sii 10
827.1 Å and Cai 10 833.4 Å lines to obtain the photospheric magnetic
field. <BR /> Results: We find that the inclination of the magnetic
field varies in the azimuthal direction in the photosphere and in the
upper chromosphere. The chromospheric variations coincide remarkably
well with the variations in the inclination of the photospheric field
and resemble the well-known spine and interspine structure in the
photospheric layers of penumbrae. The typical peak-to-peak variations
in the inclination of the magnetic field in the upper chromosphere
are found to be 10°-15°, which is roughly half the variation in
the photosphere. In contrast, the magnetic field strength of the
observed penumbra does not vary on small spatial scales in the upper
chromosphere. <BR /> Conclusions: Thanks to the high spatial resolution
of the observations that is possible with the GREGOR telescope at 1.08
microns, we find that the prominent small-scale fluctuations in the
magnetic field inclination, which are a salient part of the property
of sunspot penumbral photospheres, also persist in the chromosphere,
although at somewhat reduced amplitudes. Such a complex magnetic
configuration may facilitate penumbral chromospheric dynamic phenomena,
such as penumbral micro-jets or transient bright dots.
---------------------------------------------------------
Title: Probing deep photospheric layers of the quiet Sun with high
magnetic sensitivity
Authors: Lagg, A.; Solanki, S. K.; Doerr, H. -P.; Martínez González,
M. J.; Riethmüller, T.; Collados Vera, M.; Schlichenmaier, R.;
Orozco Suárez, D.; Franz, M.; Feller, A.; Kuckein, C.; Schmidt, W.;
Asensio Ramos, A.; Pastor Yabar, A.; von der Lühe, O.; Denker, C.;
Balthasar, H.; Volkmer, R.; Staude, J.; Hofmann, A.; Strassmeier,
K.; Kneer, F.; Waldmann, T.; Borrero, J. M.; Sobotka, M.; Verma, M.;
Louis, R. E.; Rezaei, R.; Soltau, D.; Berkefeld, T.; Sigwarth, M.;
Schmidt, D.; Kiess, C.; Nicklas, H.
2016A&A...596A...6L Altcode: 2016arXiv160506324L
Context. Investigations of the magnetism of the quiet Sun are hindered
by extremely weak polarization signals in Fraunhofer spectral
lines. Photon noise, straylight, and the systematically different
sensitivity of the Zeeman effect to longitudinal and transversal
magnetic fields result in controversial results in terms of the strength
and angular distribution of the magnetic field vector. <BR /> Aims:
The information content of Stokes measurements close to the diffraction
limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of
spatial straylight and photon noise into account. <BR /> Methods: Highly
sensitive full Stokes measurements of a quiet-Sun region at disk center
in the deep photospheric Fe I lines in the 1.56 μm region were obtained
with the infrared spectropolarimeter GRIS at the GREGOR telescope. Noise
statistics and Stokes V asymmetries were analyzed and compared to a
similar data set of the Hinode spectropolarimeter (SOT/SP). Simple
diagnostics based directly on the shape and strength of the profiles
were applied to the GRIS data. We made use of the magnetic line ratio
technique, which was tested against realistic magneto-hydrodynamic
simulations (MURaM). <BR /> Results: About 80% of the GRIS spectra
of a very quiet solar region show polarimetric signals above a 3σ
level. Area and amplitude asymmetries agree well with small-scale
surface dynamo-magneto hydrodynamic simulations. The magnetic line ratio
analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss
range with some concentrations of kilo-Gauss fields. <BR /> Conclusions:
The GRIS spectropolarimetric data at a spatial resolution of ≈0.̋4
are so far unique in the combination of high spatial resolution scans
and high magnetic field sensitivity. Nevertheless, the unavoidable
effect of spatial straylight and the resulting dilution of the weak
Stokes profiles means that inversion techniques still bear a high risk
of misinterpretating the data.
---------------------------------------------------------
Title: Three-dimensional structure of a sunspot light bridge
Authors: Felipe, T.; Collados, M.; Khomenko, E.; Kuckein, C.; Asensio
Ramos, A.; Balthasar, H.; Berkefeld, T.; Denker, C.; Feller, A.;
Franz, M.; Hofmann, A.; Joshi, J.; Kiess, C.; Lagg, A.; Nicklas, H.;
Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier,
R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki,
S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.;
von der Lühe, O.; Waldmann, T.
2016A&A...596A..59F Altcode: 2016arXiv161104803F
Context. Active regions are the most prominent manifestations of solar
magnetic fields; their generation and dissipation are fundamental
problems in solar physics. Light bridges are commonly present during
sunspot decay, but a comprehensive picture of their role in the
removal of the photospheric magnetic field is still lacking. <BR />
Aims: We study the three-dimensional configuration of a sunspot,
and in particular, its light bridge, during one of the last stages of
its decay. <BR /> Methods: We present the magnetic and thermodynamical
stratification inferred from full Stokes inversions of the photospheric
Si I 10 827 Å and Ca I 10 839 Å lines obtained with the GREGOR
Infrared Spectrograph of the GREGOR telescope at the Observatorio del
Teide, Tenerife, Spain. The analysis is complemented by a study of
continuum images covering the disk passage of the active region, which
are provided by the Helioseismic and Magnetic Imager on board the Solar
Dynamics Observatory. <BR /> Results: The sunspot shows a light bridge
with penumbral continuum intensity that separates the central umbra from
a smaller umbra. We find that in this region the magnetic field lines
form a canopy with lower magnetic field strength in the inner part. The
photospheric light bridge is dominated by gas pressure (high-β),
as opposed to the surrounding umbra, where the magnetic pressure
is higher. A convective flow is observed in the light bridge. This
flow is able to bend the magnetic field lines and to produce field
reversals. The field lines merge above the light bridge and become
as vertical and strong as in the surrounding umbra. We conclude that
this occurs because two highly magnetized regions approach each other
during the sunspot evolution. <P />Movies associated to Figs. 2 and 13
are available at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Inference of magnetic fields in the very quiet Sun
Authors: Martínez González, M. J.; Pastor Yabar, A.; Lagg, A.;
Asensio Ramos, A.; Collados, M.; Solanki, S. K.; Balthasar, H.;
Berkefeld, T.; Denker, C.; Doerr, H. P.; Feller, A.; Franz, M.;
González Manrique, S. J.; Hofmann, A.; Kneer, F.; Kuckein, C.;
Louis, R.; von der Lühe, O.; Nicklas, H.; Orozco, D.; Rezaei, R.;
Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma, M.; Waldman,
T.; Volkmer, R.
2016A&A...596A...5M Altcode: 2018arXiv180410089M
Context. Over the past 20 yr, the quietest areas of the solar surface
have revealed a weak but extremely dynamic magnetism occurring
at small scales (<500 km), which may provide an important
contribution to the dynamics and energetics of the outer layers of
the atmosphere. Understanding this magnetism requires the inference
of physical quantities from high-sensitivity spectro-polarimetric
data with high spatio-temporal resolution. <BR /> Aims: We present
high-precision spectro-polarimetric data with high spatial resolution
(0.4”) of the very quiet Sun at 1.56 μm obtained with the GREGOR
telescope to shed some light on this complex magnetism. <BR /> Methods:
We used inversion techniques in two main approaches. First, we assumed
that the observed profiles can be reproduced with a constant magnetic
field atmosphere embedded in a field-free medium. Second, we assumed
that the resolution element has a substructure with either two constant
magnetic atmospheres or a single magnetic atmosphere with gradients of
the physical quantities along the optical depth, both coexisting with
a global stray-light component. <BR /> Results: Half of our observed
quiet-Sun region is better explained by magnetic substructure within
the resolution element. However, we cannot distinguish whether this
substructure comes from gradients of the physical parameters along the
line of sight or from horizontal gradients (across the surface). In
these pixels, a model with two magnetic components is preferred, and
we find two distinct magnetic field populations. The population with
the larger filling factor has very weak ( 150 G) horizontal fields
similar to those obtained in previous works. We demonstrate that the
field vector of this population is not constrained by the observations,
given the spatial resolution and polarimetric accuracy of our data. The
topology of the other component with the smaller filling factor is
constrained by the observations for field strengths above 250 G:
we infer hG fields with inclinations and azimuth values compatible
with an isotropic distribution. The filling factors are typically
below 30%. We also find that the flux of the two polarities is not
balanced. From the other half of the observed quiet-Sun area 50% are
two-lobed Stokes V profiles, meaning that 23% of the field of view
can be adequately explained with a single constant magnetic field
embedded in a non-magnetic atmosphere. The magnetic field vector and
filling factor are reliable inferred in only 50% based on the regular
profiles. Therefore, 12% of the field of view harbour hG fields with
filling factors typically below 30%. At our present spatial resolution,
70% of the pixels apparently are non-magnetised.
---------------------------------------------------------
Title: Fitting peculiar spectral profiles in He I 10830Å absorption
features
Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.;
Collados, M.; Denker, C.; Fischer, C. E.; Gömöry, P.; Diercke, A.;
Bello González, N.; Schlichenmaier, R.; Balthasar, H.; Berkefeld, T.;
Feller, A.; Hoch, S.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.;
Orozco Suárez, D.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma,
M.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1057G Altcode: 2016arXiv160300679G
The new generation of solar instruments provides better
spectral, spatial, and temporal resolution for a better
understanding of the physical processes that take place on the
Sun. Multiple-component profiles are more commonly observed with these
instruments. Particularly, the He I 10830 Å triplet presents such
peculiar spectral profiles, which give information on the velocity
and magnetic fine structure of the upper chromosphere. The purpose
of this investigation is to describe a technique to efficiently fit
the two blended components of the He I 10830 Å triplet, which are
commonly observed when two atmospheric components are located within
the same resolution element. The observations used in this study were
taken on 2015 April 17 with the very fast spectroscopic mode of the
GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar
telescope, located at the Observatorio del Teide, Tenerife, Spain. We
apply a double-Lorentzian fitting technique using Levenberg-Marquardt
least-squares minimization. This technique is very simple and much
faster than inversion codes. Line-of-sight Doppler velocities can
be inferred for a whole map of pixels within just a few minutes. Our
results show sub- and supersonic downflow velocities of up to 32 km
s<SUP>-1</SUP> for the fast component in the vicinity of footpoints of
filamentary structures. The slow component presents velocities close
to rest.
---------------------------------------------------------
Title: Inversion of Stokes profiles with systematic effects
Authors: Asensio Ramos, A.; de la Cruz Rodríguez, J.; Martínez
González, M. J.; Pastor Yabar, A.
2016A&A...590A..87A Altcode: 2016arXiv160405470A
Quantitative thermodynamical, dynamical and magnetic properties of the
solar and stellar plasmas are obtained by interpreting their emergent
non-polarized and polarized spectrum. This inference requires the
selection of a set of spectral lines that are particularly sensitive to
the physical conditions in the plasma and a suitable parametric model
of the solar/stellar atmosphere. Nonlinear inversion codes are then
used to fit the model to the observations. However, the presence of
systematic effects, like nearby or blended spectral lines, telluric
absorption, or incorrect correction of the continuum, among others,
can strongly affect the results. We present an extension to current
inversion codes that can deal with these effects in a transparent
way. The resulting algorithm is very simple and can be applied to any
existing inversion code with the addition of a few lines of code as
an extra step in each iteration.
---------------------------------------------------------
Title: Flows in and around Active Region NOAA12118 Observed with
the GREGOR Solar Telescope and SDO/HMI
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González
Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke,
A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor
Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert,
M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016ASPC..504...29V Altcode: 2016arXiv160301109V
Accurate measurements of magnetic and velocity fields in and around
solar active regions are key to unlocking the mysteries of the
formation and the decay of sunspots. High spatial resolution images
and spectral sequences with a high cadence obtained with the GREGOR
solar telescope give us an opportunity to scrutinize 3-D flow fields
with local correlation tracking and imaging spectroscopy. We present
GREGOR early science data acquired in 2014 July - August with the GREGOR
Fabry-Pérot Interferometer and the Blue Imaging Channel. Time-series
of blue continuum (λ 450.6 nm) images of the small active region
NOAA 12118 were restored with the speckle masking technique to derive
horizontal proper motions and to track the evolution of morphological
changes. In addition, high-resolution observations are discussed in
the context of synoptic data from the Solar Dynamics Observatory.
---------------------------------------------------------
Title: The WEBT campaign on the BL Lac object PG 1553+113 in 2013. An
analysis of the enigmatic synchrotron emission
Authors: Raiteri, C. M.; Stamerra, A.; Villata, M.; Larionov, V. M.;
Acosta-Pulido, J. A.; Arévalo, M. J.; Arkharov, A. A.; Bachev, R.;
Benítez, E.; Bozhilov, V. V.; Borman, G. A.; Buemi, C. S.; Calcidese,
P.; Carnerero, M. I.; Carosati, D.; Chigladze, R. A.; Damljanovic, G.;
Di Paola, A.; Doroshenko, V. T.; Efimova, N. V.; Ehgamberdiev, Sh. A.;
Giroletti, M.; González-Morales, P. A.; Grinon-Marin, A. B.; Grishina,
T. S.; Hiriart, D.; Ibryamov, S.; Klimanov, S. A.; Kopatskaya, E. N.;
Kurtanidze, O. M.; Kurtanidze, S. O.; Kurtenkov, A. A.; Larionova,
L. V.; Larionova, E. G.; Lázaro, C.; Lähteenmäki, A.; Leto,
P.; Markovic, G.; Mirzaqulov, D. O.; Mokrushina, A. A.; Morozova,
D. A.; Mújica, R.; Nazarov, S. V.; Nikolashvili, M. G.; Ohlert,
J. M.; Ovcharov, E. P.; Paiano, S.; Pastor Yabar, A.; Prandini, E.;
Ramakrishnan, V.; Sadun, A. C.; Semkov, E.; Sigua, L. A.; Strigachev,
A.; Tammi, J.; Tornikoski, M.; Trigilio, C.; Troitskaya, Yu. V.;
Troitsky, I. S.; Umana, G.; Velasco, S.; Vince, O.
2015MNRAS.454..353R Altcode: 2015arXiv150902706R
A multifrequency campaign on the BL Lac object PG 1553+113 was organized
by the Whole Earth Blazar Telescope (WEBT) in 2013 April-August,
involving 19 optical, two near-IR, and three radio telescopes. The aim
was to study the source behaviour at low energies during and around the
high-energy observations by the Major Atmospheric Gamma-ray Imaging
Cherenkov telescopes in April-July. We also analyse the UV and X-ray
data acquired by the Swift and XMM-Newton satellites in the same
period. The WEBT and satellite observations allow us to detail the
synchrotron emission bump in the source spectral energy distribution
(SED). In the optical, we found a general bluer-when-brighter trend. The
X-ray spectrum remained stable during 2013, but a comparison with
previous observations suggests that it becomes harder when the X-ray
flux increases. The long XMM-Newton exposure reveals a curved X-ray
spectrum. In the SED, the XMM-Newton data show a hard near-UV spectrum,
while Swift data display a softer shape that is confirmed by previous
Hubble Space Telescope/Cosmic Origins Spectrograph and International
Ultraviolet Explorer observations. Polynomial fits to the optical-X-ray
SED show that the synchrotron peak likely lies in the 4-30 eV energy
range, with a general shift towards higher frequencies for increasing
X-ray brightness. However, the UV and X-ray spectra do not connect
smoothly. Possible interpretations include: (i) orientation effects,
(ii) additional absorption, (iii) multiple emission components, and (iv)
a peculiar energy distribution of relativistic electrons. We discuss
the first possibility in terms of an inhomogeneous helical jet model.
---------------------------------------------------------
Title: Where are the solar magnetic poles?
Authors: Pastor Yabar, A.; Martinez Gonzalez, M. J.; Collados, M.
2015MNRAS.453L..69P Altcode: 2018arXiv180409748P
Regardless of the physical origin of stellar magnetic fields -
fossil or dynamo induced - an inclination angle between the magnetic
and rotation axes is very often observed. Absence of observational
evidence in this direction in the solar case has led to generally assume
that its global magnetic field and rotation axes are well aligned. We
present the detection of a monthly periodic signal of the photospheric
solar magnetic field at all latitudes, and especially near the poles,
revealing that the main axis of the Sun's magnetic field is not aligned
with the surface rotation axis. This result reinforces the view of our
Sun as a common intermediate-mass star. Furthermore, this detection
challenges and imposes a strong observational constraint to modern
solar dynamo theories.
---------------------------------------------------------
Title: Multiwavelength behaviour of the blazar OJ 248 from radio
to γ-rays
Authors: Carnerero, M. I.; Raiteri, C. M.; Villata, M.; Acosta-Pulido,
J. A.; D'Ammando, F.; Smith, P. S.; Larionov, V. M.; Agudo, I.;
Arévalo, M. J.; Arkharov, A. A.; Bach, U.; Bachev, R.; Benítez,
E.; Blinov, D. A.; Bozhilov, V.; Buemi, C. S.; Bueno Bueno, A.;
Carosati, D.; Casadio, C.; Chen, W. P.; Damljanovic, G.; di Paola, A.;
Efimova, N. V.; Ehgamberdiev, Sh. A.; Giroletti, M.; Gómez, J. L.;
González-Morales, P. A.; Grinon-Marin, A. B.; Grishina, T. S.;
Gurwell, M. A.; Hiriart, D.; Hsiao, H. Y.; Ibryamov, S.; Jorstad,
S. G.; Joshi, M.; Kopatskaya, E. N.; Kurtanidze, O. M.; Kurtanidze,
S. O.; Lähteenmäki, A.; Larionova, E. G.; Larionova, L. V.; Lázaro,
C.; Leto, P.; Lin, C. S.; Lin, H. C.; Manilla-Robles, A. I.; Marscher,
A. P.; McHardy, I. M.; Metodieva, Y.; Mirzaqulov, D. O.; Mokrushina,
A. A.; Molina, S. N.; Morozova, D. A.; Nikolashvili, M. G.; Orienti,
M.; Ovcharov, E.; Panwar, N.; Pastor Yabar, A.; Puerto Giménez,
I.; Ramakrishnan, V.; Richter, G. M.; Rossini, M.; Sigua, L. A.;
Strigachev, A.; Taylor, B.; Tornikoski, M.; Trigilio, C.; Troitskaya,
Yu. V.; Troitsky, I. S.; Umana, G.; Valcheva, A.; Velasco, S.; Vince,
O.; Wehrle, A. E.; Wiesemeyer, H.
2015MNRAS.450.2677C Altcode: 2015arXiv150500916C
We present an analysis of the multiwavelength behaviour of the blazar
OJ 248 at z = 0.939 in the period 2006-2013. We use low-energy data
(optical, near-infrared, and radio) obtained by 21 observatories
participating in the Gamma-Ray Large Area Space Telescope (GLAST)-AGILE
Support Program of the Whole Earth Blazar Telescope, as well as data
from the Swift (optical-UV and X-rays) and Fermi (γ-rays) satellites,
to study flux and spectral variability and correlations among emissions
in different bands. We take into account the effect of absorption by the
Damped Lyman α intervening system at z = 0.525. Two major outbursts
were observed in 2006-2007 and in 2012-2013 at optical and near-IR
wavelengths, while in the high-frequency radio light curves prominent
radio outbursts are visible peaking at the end of 2010 and beginning of
2013, revealing a complex radio-optical correlation. Cross-correlation
analysis suggests a delay of the optical variations after the γ-ray
ones of about a month, which is a peculiar behaviour in blazars. We
also analyse optical polarimetric and spectroscopic data. The average
polarization percentage P is less than 3 per cent, but it reaches ∼19
per cent during the early stage of the 2012-2013 outburst. A vague
correlation of P with brightness is observed. There is no preferred
electric vector polarization angle and during the outburst the linear
polarization vector shows wide rotations in both directions, suggesting
a complex behaviour/structure of the jet and possible turbulence. The
analysis of 140 optical spectra acquired at the Steward Observatory
reveals a strong Mg II broad emission line with an essentially stable
flux of 6.2 × 10<SUP>- 15</SUP> erg cm<SUP>- 2</SUP> s<SUP>- 1</SUP>
and a full width at half-maximum of 2053 km s<SUP>- 1</SUP>.
---------------------------------------------------------
Title: Infrared properties of blazars: putting the GASP-WEBT sources
into context
Authors: Raiteri, C. M.; Villata, M.; Carnerero, M. I.;
Acosta-Pulido, J. A.; Larionov, V. M.; D'Ammando, F.; Arévalo, M. J.;
Arkharov, A. A.; Bueno Bueno, A.; Di Paola, A.; Efimova, N. V.;
González-Morales, P. A.; Gorshanov, D. L.; Grinon-Marin, A. B.;
Lázaro, C.; Manilla-Robles, A.; Pastor Yabar, A.; Puerto Giménez,
I.; Velasco, S.
2014MNRAS.442..629R Altcode: 2014arXiv1405.4168R
The infrared properties of blazars can be studied from the statistical
point of view with the help of sky surveys, like that provided
by the Wide-field Infrared Survey Explorer and the Two Micron All
Sky Survey. However, these sources are known for their strong and
unpredictable variability, which can be monitored for a handful of
objects only. In this paper, we consider the 28 blazars (14 BL Lac
objects and 14 flat-spectrum radio quasars, FSRQs) that are regularly
monitored by the GLAST-AGILE Support Program (GASP) of the Whole Earth
Blazar Telescope since 2007. They show a variety of infrared colours,
redshifts, and infrared-optical spectral energy distributions (SEDs),
and thus represent an interesting mini-sample of bright blazars that
can be investigated in more detail. We present near-IR light curves
and colours obtained by the GASP from 2007 to 2013, and discuss the
infrared-optical SEDs. These are analysed with the aim of understanding
the interplay among different emission components. BL Lac SEDs are
accounted for by synchrotron emission plus an important contribution
from the host galaxy in the closest objects, and dust signatures
in 3C 66A and Mrk 421. FSRQ SEDs require synchrotron emission with
the addition of a quasar-like contribution, which includes radiation
from a generally bright accretion disc (νL<SUB>ν</SUB> up to ∼4
× 10<SUP>46</SUP> erg s<SUP>-1</SUP>), broad-line region, and a
relatively weak dust torus.
