209 research outputs found
Blazar Variability: A Study of Non-stationarity and the Flux-RMS Relation
We analyze X-ray light curves of the blazars Mrk 421, PKS 2155-304, and 3C
273 using observations by the Soft X-ray Telescope on board AstroSat and
archival XMM-Newton data. We use light curves of length 30-90 ks each from 3-4
epochs for all three blazars. We apply the autoregressive integrated moving
average (ARIMA) model which indicates the variability is consistent with short
memory processes for most of the epochs. We show that the power spectral
density (PSD) of the X-ray variability of the individual blazars are consistent
within uncertainties across the epochs. This implies that the construction of
broadband PSD using light curves from different epochs is accurate. However,
using certain properties of the variance of the light curves and its segments,
we show that the blazars exhibit hints of non-stationarity beyond that due to
their characteristic red noise nature in some of those observations. We find a
linear relationship between the root-mean-squared amplitude of variability at
shorter timescales and the mean flux level at longer timescales for light
curves of Mrk 421 across epochs separated by decades as well as light curves
spanning 5 days and 10 yr. The presence of flux-rms relation over very
different timescales may imply that, similar to the X-ray binaries and Seyfert
galaxies, longer and shorter timescale variability are connected in blazars.Comment: 12 pages, 4 figures. Accepted for publication in the Astrophysical
Journa
Shear Viscosity of hadronic matter at finite temperature and magnetic field
We calculate the transport coefficient of hadronic matter in the presence of
temperature and magnetic field using the linear sigma model. In the relaxation
time approximation, we estimate the shear viscosity over entropy density
. The point-like interaction rates of hadrons are evaluated through the
-matrix approach in the presence of a magnetic field to obtain the
temperature and magnetic field-dependent relaxation time. We observe that the
transport coefficients are anisotropic in the presence of the magnetic field.
We calculate the temperature and magnetic field-dependent anisotropic shear
viscosity coefficients by incorporating the estimated relaxation time. The
value of viscosity over entropy density is lower in the presence of a magnetic
field than the value of it in a thermal medium. The behavior of the
perpendicular components of the shear viscosity coefficient is also discussed.
We consider the temperature-dependent hadron masses from mean-field effects in
this work.Comment: 20 pages, 3 figure
Heavy quark potential and LQCD based quark condensate at finite magnetic field
We have studied various properties of heavy quarkonia in hot and magnetized
quark gluon plasma. Inverse magnetic catalysis (IMC) effect is incorporated by
modifying the effective quark masses. Then we obtain the real and imaginary
part of the heavy quark potential. After evaluating binding energy and decay
width we obtain the dissociation temperature of heavy quarkonia in presence of
magnetic field.Comment: 15 pages, 7 figure
Anisotropic tomography of heavy quark dissociation by using general propagator structure at finite magnetic field
In this work we have explored the imaginary part of the Heavy Quark (HQ)
potential and subsequently the dissociation of heavy quarkonia, within the most
general scenario of magnetized hot medium. We have used the general structure
of the gauge boson propagator in a hot magnetized medium and derived the most
general result for the imaginary HQ potential and the decay width for the heavy
quarkonia. In the process we have investigated the rich anisotropic structure
of the complex HQ potential which explicitly depends on the longitudinal and
transverse distance. We have also compared our full structure rich result with
various approximated results available in the literature and explained the
differences between them.Comment: 23 pages, 9 figure
Collective modes of gluons in an anisotropic thermo-magnetic medium
We study the collective modes of gluon in an anisotropic thermal medium in
presence of a constant background magnetic field using the hard-thermal loop
(HTL) perturbation theory. The momentum space anisotropy of the medium has been
incorporated through the generalized Romatschke-Strickland' form of the
distribution function, whereas, the magnetic modification arising from the
quark loop contribution has been taken into account in the lowest Landau level
approximation. We consider two special cases: (i) a spheroidal anisotropy with
the anisotropy vector orthogonal to the external magnetic field and (ii) an
ellipsoidal anisotropy with two mutually orthogonal vectors describing
aniostropies along and orthogonal to the field direction. The general structure
of the polarization tensor in both cases are equivalent and consists of six
independent basis tensors. We find that the introduction of momentum anisotropy
ingrains azimuthal angular dependence in the thermo-magnetic collective modes.
Our study suggests that the presence of a strong background magnetic field can
significantly reduce the growth rate of the unstable modes which may have
important implications in the equilibration of magnetized quark-gluon plasma.Comment: 15 pages, 6 figure
Impact of chiral asymmetry and magnetic field on passage of an energetic test parton in a QCD medium
We study the dependence of collisional energy loss of a test parton moving
with a high velocity on the chiral imbalance and magnetic field in the QCD
medium. A semi-classical approach is adopted to estimate the parton energy loss
that takes into account the back-reaction on the parton due to the polarization
effects of the QCD medium while traversing through the medium. We find that the
motion of the parton is sensitive to the chiral asymmetry in the medium.
Further, we investigate the effect of magnetic field-induced anisotropy on the
energy transfer between the moving parton and the medium. Our results show that
the energy loss of the parton is strongly influenced by the strength of the
magnetic field as well as the relative orientation of the motion of the parton
and the direction of the magnetic field in the medium.Comment: 9 pages, 5 figure
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