589 research outputs found
X-Ray and Gamma-Ray Polarization in Leptonic and Hadronic Jet Models of Blazars
We present a theoretical analysis of the expected X-ray and gamma-ray
polarization signatures resulting from synchrotron self-Compton emission in
leptonic models, compared to the polarization signatures from proton
synchrotron and cascade synchrotron emission in hadronic models for blazars.
Source parameters resulting from detailed spectral-energy-distribution modeling
are used to calculate photon-energy-dependent upper limits on the degree of
polarization, assuming a perfectly organized, mono-directional magnetic field.
In low-synchrotron-peaked blazars, hadronic models exhibit substantially higher
maximum degrees of X-ray and gamma-ray polarization than leptonic models, which
may be within reach for existing X-ray and gamma-ray polarimeters. In
high-synchrotron-peaked blazars (with electron-synchrotron-dominated X-ray
emission), leptonic and hadronic models predict the same degree of X-ray
polarization, but substantially higher maximum gamma-ray polarization in
hadronic models than leptonic ones. These predictions are particularly relevant
in view of the new generation of balloon-borne X-ray polarimeters (and possibly
GEMS, if revived), and the ability of Fermi-LAT to measure gamma-ray
polarization at < 200 MeV. We suggest observational strategies combining
optical, X-ray, gamma-ray polarimetry to determine the degree of ordering of
the magnetic field and to distinguish between leptonic and hadronic high-energy
emission.Comment: Accepted for publication in The Astrophysical Journa
Radiation and Polarization Signatures of 3D Multi-zone Time-dependent Hadronic Blazar Model
We present a newly developed time-dependent three-dimensional multi-zone
hadronic blazar emission model. By coupling a Fokker-Planck based
lepto-hadronic particle evolution code 3DHad with a polarization-dependent
radiation transfer code, 3DPol, we are able to study the time-dependent
radiation and polarization signatures of a hadronic blazar model for the first
time. Our current code is limited to parameter regimes in which the hadronic
-ray output is dominated by proton synchrotron emission, neglecting
pion production. Our results demonstrate that the time-dependent flux and
polarization signatures are generally dominated by the relation between the
synchrotron cooling and the light crossing time scale, which is largely
independent of the exact model parameters. We find that unlike the low-energy
polarization signatures, which can vary rapidly in time, the high-energy
polarization signatures appear stable. As a result, future high-energy
polarimeters may be able to distinguish such signatures from the lower and more
rapidly variable polarization signatures expected in leptonic models.Comment: Accepted for Publication in The Astrophysical Journa
Synchrotron Polarization in Blazars
We present a detailed analysis of time- and energy-dependent synchrotron
polarization signatures in a shock-in-jet model for gamma-ray blazars. Our
calculations employ a full 3D radiation transfer code, assuming a helical
magnetic field throughout the jet. The code considers synchrotron emission from
an ordered magnetic field, and takes into account all light-travel-time and
other relevant geometric effects, while the relevant synchrotron self-Compton
and external Compton effects are taken care of with the 2D MCFP code. We
consider several possible mechanisms through which a relativistic shock
propagating through the jet may affect the jet plasma to produce a synchrotron
and high-energy flare. Most plausibly, the shock is expected to lead to a
compression of the magnetic field, increasing the toroidal field component and
thereby changing the direction of the magnetic field in the region affected by
the shock. We find that such a scenario leads to correlated synchrotron + SSC
flaring, associated with substantial variability in the synchrotron
polarization percentage and position angle. Most importantly, this scenario
naturally explains large PA rotations by > 180 deg., as observed in connection
with gamma-ray flares in several blazars, without the need for bent or helical
jet trajectories or other non-axisymmetric jet features.Comment: Submitted to Ap
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