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Title: Linear Polarization, Circular Polarization, and Depolarization of Gamma-ray Bursts: A Simple Case of Jitter Radiation

Abstract

Linear and circular polarizations of gamma-ray bursts (GRBs) have been detected recently. We adopt a simplified model to investigate GRB polarization characteristics in this paper. A compressed two-dimensional turbulent slab containing stochastic magnetic fields is considered, and jitter radiation can produce the linear polarization under this special magnetic field topology. Turbulent Faraday rotation measure (RM) of this slab makes strong wavelength-dependent depolarization. The jitter photons can also scatter with those magnetic clumps inside the turbulent slab, and a nonzero variance of the Stokes parameter V can be generated. Furthermore, the linearly and circularly polarized photons in the optical and radio bands may suffer heavy absorptions from the slab. Thus we consider the polarized jitter radiation transfer processes. Finally, we compare our model results with the optical detections of GRB 091018, GRB 121024A, and GRB 131030A. We suggest simultaneous observations of GRB multi-wavelength polarization in the future.

Authors:
;  [1]
  1. Yunnan Observatories, Chinese Academy of Sciences, 650011 Kunming, Yunnan Province (China)
Publication Date:
OSTI Identifier:
22661218
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 838; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; COMPARATIVE EVALUATIONS; COSMIC GAMMA BURSTS; DEPOLARIZATION; DETECTION; FARADAY EFFECT; GAMMA RADIATION; MAGNETIC FIELDS; PHOTONS; POLARIZATION; SHOCK WAVES; STOCHASTIC PROCESSES; STOKES PARAMETERS; TOPOLOGY; TURBULENCE; TWO-DIMENSIONAL CALCULATIONS; WAVELENGTHS

Citation Formats

Mao, Jirong, and Wang, Jiancheng, E-mail: jirongmao@mail.ynao.ac.cn. Linear Polarization, Circular Polarization, and Depolarization of Gamma-ray Bursts: A Simple Case of Jitter Radiation. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA6628.
Mao, Jirong, & Wang, Jiancheng, E-mail: jirongmao@mail.ynao.ac.cn. Linear Polarization, Circular Polarization, and Depolarization of Gamma-ray Bursts: A Simple Case of Jitter Radiation. United States. doi:10.3847/1538-4357/AA6628.
Mao, Jirong, and Wang, Jiancheng, E-mail: jirongmao@mail.ynao.ac.cn. Sat . "Linear Polarization, Circular Polarization, and Depolarization of Gamma-ray Bursts: A Simple Case of Jitter Radiation". United States. doi:10.3847/1538-4357/AA6628.
@article{osti_22661218,
title = {Linear Polarization, Circular Polarization, and Depolarization of Gamma-ray Bursts: A Simple Case of Jitter Radiation},
author = {Mao, Jirong and Wang, Jiancheng, E-mail: jirongmao@mail.ynao.ac.cn},
abstractNote = {Linear and circular polarizations of gamma-ray bursts (GRBs) have been detected recently. We adopt a simplified model to investigate GRB polarization characteristics in this paper. A compressed two-dimensional turbulent slab containing stochastic magnetic fields is considered, and jitter radiation can produce the linear polarization under this special magnetic field topology. Turbulent Faraday rotation measure (RM) of this slab makes strong wavelength-dependent depolarization. The jitter photons can also scatter with those magnetic clumps inside the turbulent slab, and a nonzero variance of the Stokes parameter V can be generated. Furthermore, the linearly and circularly polarized photons in the optical and radio bands may suffer heavy absorptions from the slab. Thus we consider the polarized jitter radiation transfer processes. Finally, we compare our model results with the optical detections of GRB 091018, GRB 121024A, and GRB 131030A. We suggest simultaneous observations of GRB multi-wavelength polarization in the future.},
doi = {10.3847/1538-4357/AA6628},
journal = {Astrophysical Journal},
number = 2,
volume = 838,
place = {United States},
year = {Sat Apr 01 00:00:00 EDT 2017},
month = {Sat Apr 01 00:00:00 EDT 2017}
}
  • A high degree of polarization of gamma-ray burst (GRB) prompt emission has been confirmed in recent years. In this paper, we apply jitter radiation to study the polarization feature of GRB prompt emission. In our framework, relativistic electrons are accelerated by turbulent acceleration. Random and small-scale magnetic fields are generated by turbulence. We further determine that the polarization property of GRB prompt emission is governed by the configuration of the random and small-scale magnetic fields. A two-dimensional compressed slab, which contains a stochastic magnetic field, is applied in our model. If the jitter condition is satisfied, the electron deflection anglemore » in the magnetic field is very small and the electron trajectory can be treated as a straight line. A high degree of polarization can be achieved when the angle between the line of sight and the slab plane is small. Moreover, micro-emitters with mini-jet structures are considered to be within a bulk GRB jet. The jet 'off-axis' effect is intensely sensitive to the observed polarization degree. We discuss the depolarization effect on GRB prompt emission and afterglow. We also speculate that the rapid variability of GRB prompt polarization may be correlated with the stochastic variability of the turbulent dynamo or the magnetic reconnection of plasmas.« less
  • The origin of rapid spectral variability and certain spectral correlations of prompt gamma-ray burst emission remains an intriguing question. The recently proposed theoretical model of the prompt emission is built upon unique spectral properties of jitter radiation-the radiation from small-scale magnetic fields generated at a site of strong energy release (e.g., a relativistic collisionless shock in baryonic or pair-dominated ejecta, or a reconnection site in a magnetically dominated outflow). Here we present the results of implementation of the model. We show that anisotropy of the jitter radiation pattern and relativistic shell kinematics altogether produce effects commonly observed in time-resolved spectramore » of the prompt emission, e.g., the softening of the spectrum below the peak energy within individual pulses in the prompt light curve, the so-called 'tracking' behavior (correlation of the observed flux with other spectral parameters), the emergence of hard, synchrotron-violating spectra at the beginning of individual spikes. Several observational predictions of the model are discussed.« less
  • We revisit the radiation mechanism of relativistic electrons in the stochastic magnetic field and apply it to the high-energy emissions of gamma-ray bursts (GRBs). We confirm that jitter radiation is a possible explanation for GRB prompt emission in the condition of a large electron deflection angle. In the turbulent scenario, the radiative spectral property of GRB prompt emission is decided by the kinetic energy spectrum of turbulence. The intensity of the random and small-scale magnetic field is determined by the viscous scale of the turbulent eddy. The microphysical parameters {epsilon}{sub e} and {epsilon}{sub B} can be obtained. The acceleration andmore » cooling timescales are estimated as well. Due to particle acceleration in magnetized filamentary turbulence, the maximum energy released from the relativistic electrons can reach a value of about 10{sup 14} eV. The GeV GRBs are possible sources of high-energy cosmic-ray.« less
  • The gamma-ray flares of the Crab nebula detected by the Fermi and AGILE satellites challenge our understanding of the physics of pulsars and their nebulae. The central problem is that the peak energy of the flares exceeds the maximum energy E {sub c} determined by synchrotron radiation loss. However, when turbulent magnetic fields exist with scales {lambda}{sub B} smaller than 2{pi}mc {sup 2}/eB, jitter radiation can emit photons with energies higher than E {sub c}. The scale required for the Crab flares is about two orders of magnitude less than the wavelength of the striped wind. We discuss a modelmore » in which the flares are triggered by plunging the high-density blobs into the termination shock. The observed hard spectral shape may be explained by the jitter mechanism. We make three observational predictions: first, the polarization degree will become lower in flares; second, no counterpart will be seen in TeV-PeV range; and third, the flare spectrum will not be harder than {nu}F {sub {nu}}{proportional_to}{nu}{sup 1}.« less