Synchrotron Polarization of Relativistic Thermal Electrons

Mao, J.; Wang, Jiancheng

doi:10.3847/1538-4357/aaa96c

Cited by 7 publications

(10 citation statements)

References 52 publications

(38 reference statements)

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“…The high polarisation fraction suggests that the magnetic field is ordered on the angular scale of 1/Γ. According to the discussions presented in section 6.2, we find that the second episode of emission is likely to be synchrotron produced by the energetic electrons generated in the internal shocks in the optically thin region of the outflow, as they cool in the large scale ordered magnetic fields originating from the central engine (Toma et al 2009;Granot 2003;Mao & Wang 2018;Gill et al 2019). The cutoff observed in the spectrum can be related to the intrinsic pair opacity created via photon-photon annihilation in the optically thin region at the dissipation site.…”

Section: Second Emission Episodesupporting

confidence: 63%

Spectropolarimetric analysis of prompt emission of GRB 160325A: jet with evolving environment of internal shocks

Sharma

Iyyani

Bhattacharya

et al. 2020

Monthly Notices of the Royal Astronomical Society

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GRB 160325A is the only bright burst detected by AstroSat CZT Imager in its primary field of view to date. In this work, we present the spectral and polarimetric analysis of the prompt emission of the burst using AstroSat, Fermi and Niel Gehrels Swift observations. The prompt emission consists of two distinct emission episodes separated by a few seconds of quiescent/ mild activity period. The first emission episode shows a thermal component as well as a low polarisation fraction of PF < 37 % at 1.5 σ confidence level. On the other hand, the second emission episode shows a non-thermal spectrum and is found to be highly polarised with PF > 43 % at 1.5σ confidence level. We also study the afterglow properties of the jet using Swift/XRT data. The observed jet break suggests that the jet is pointed towards the observer and has an opening angle of 1.2 • for an assumed redshift, z = 2. With composite modelling of polarisation, spectrum of the prompt emission and the afterglow, we infer that the first episode of emission originates from the photosphere with localised dissipation happening below it, and the second from the optically thin region above the photosphere. The photospheric emission is generated mainly by inverse Compton scattering, whereas the emission in the optically thin region is produced by the synchrotron process. The low radiation efficiency of the burst suggests that the outflow remains baryonic dominated throughout the burst duration with only a subdominant Poynting flux component, and the kinetic energy of the jet is likely dissipated via internal shocks which evolves from an optically thick to optically thin environment within the jet.

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Section: Second Emission Episodesupporting

confidence: 63%

Spectropolarimetric analysis of prompt emission of GRB 160325A: jet with evolving environment of internal shocks

Sharma

Iyyani

Bhattacharya

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…While the thermal electrons dominate the circular polarization if γ th is approaching to γ max . We have investigated the properties of the electron energy distributions as a function of γ th and Θ in the Figure 1 of Mao & Wang (2018). We note that the electron drift velocity is not included in our calculation.…”

Section: Circular Polarizationmentioning

confidence: 99%

“…We take the intrinsic linear polarization results derived by the hybrid electron energy distribution from Mao & Wang (2018). We combine the linear polarization results of Mao & Wang (2018) with the circular polarization results from this paper.…”

Section: Polarization Radiative Transfermentioning

confidence: 99%

“…A hybrid distribution of thermal-nonthermal electrons should be considered in reality. Mao & Wang (2018) have computed the synchrotron polarization properties in detail when the hybrid thermal-nonthermal electron energy distribution is adopted. In that work, the linear polarization degrees dominated by the thermal/nonthermal electrons were presented in the radio, optical, X-ray and γ-ray bands.…”

Section: Introductionmentioning

confidence: 99%

“…In that work, the linear polarization degrees dominated by the thermal/nonthermal electrons were presented in the radio, optical, X-ray and γ-ray bands. As a follow-up work of Mao & Wang (2018), this paper focuses on two issues. First, circular polarization of synchrotron radiation is not negligible.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Synchrotron Polarization Radiative Transfer: Relativistic Thermal Electron Contribution

Mao¹,

Covino²,

Wang³

2018

ApJ

Self Cite

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Relativistic thermal electrons moving in a large-scale magnetic field can produce synchrotron radiation. Linear synchrotron polarization can also be produced by the relativistic thermal electrons. In this paper, we utilize a hybrid thermalnonthermal electron energy distribution to calculate circular synchrotron polarization. We further compute the radiative transfer of the synchrotron polarization in the optical and radio bands when we consider the contribution of the thermal electrons. We attempt to apply the polarization results to some astrophysical objects, such as kilonova like AT 2017gfo/GW170817, the fast radio burst (FRB), the Gamma-ray burst (GRB) afterglow, and the supernova remnant (SNR). The large optical depth of radiative transfer effects the small polarization degrees of these populations when the media surrounding the synchrotron sources take heavy absorption to the polarized photons. We need a strong magnetic field in our model to reproduce the linear and circular polarization properties that were observed in FRB 140514. This indicates that FRBs have a neutron star origin.

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The polarization-angle flip in GRB prompt emission

Cheng,

Zhao,

Mao

et al. 2024

A&A

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In recent years, some polarization measurements of gamma-ray bursts (GRBs) have been reported, and the polarization-angle (PA) rotation in the prompt emission phase has been found in several bursts. The physical mechanism of the PA evolution is still unclear. In this work, we studied the origin of the PA rotation in a toroidal magnetic field. We aim to provide an explanation for the PA rotation in GRBs and find the physical conditions that lead to the rotation by 90 degrees in the toroidal magnetic-field (MF) model. Moreover, we present some observable polarization properties in the MF model that can be tested in the future. We calculated the instantaneous polarization degree (PD) from a top-hat jet with different normalized viewing angles ($q= jet opening angles ($ and jet Lorentz factors (Gamma ) in three wavebands. When the PD changes between positive and negative values, it means that the PA flips by 90 degrees. On these grounds, we can summarize the range of parameters required for these PA flips. Considering these parameter conditions, we can further estimate the observed rate of the GRBs exhibiting such PA rotations. We find that the PA rotation in the toroidal MF is primarily related to three critical factors: the viewing angle, the jet opening angle, and the jet Lorentz factor. Additionally, the PA can experience flips of 90 degrees twice. The conditions for the flips are $q 0.5$ (except for $q 1$) and $y_j =( 4$. However, the two flips in the PA might not be concurrently observable due to the constraint of flux. Taking these conditions into account and assuming a random orientation between the jet axis and the line of sight (LOS), we obtain a theoretical upper limit (without any constraints) for the observed rate of GRBs in the X-ray or gamma -ray band displaying the flips in PA as ch 80<!PCT!>$. We further constrain the observed rate as ch 16<!PCT!>$ according to the maximal post-flip polarized flux level, where the observed rate of single and double flips each account for $ 8<!PCT!>$. It should be noted that the observed rates are different in various wavebands. The observed rate of the second PA flip in the optical bands should be higher than that in the X-ray or gamma -ray band since the flux in the optical band declines much slower than that in the X-ray or gamma -ray band. Moreover, when the LOS is close to the jet edge ($q 1$), it is the easiest case in which to observe the 90-degree PA flip due to the relatively high post-flip polarized flux level. The first and second PA flips in a GRB pulse are most likely to occur at the observed times of obs t_ peak $ and $ t_ peak $, respectively, where $t_ peak $ is the peak time of the pulse. It is also noted that the PA flip would not happen before the peak time.

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Synchrotron Polarization of Relativistic Thermal Electrons

Cited by 7 publications

References 52 publications

Spectropolarimetric analysis of prompt emission of GRB 160325A: jet with evolving environment of internal shocks

Spectropolarimetric analysis of prompt emission of GRB 160325A: jet with evolving environment of internal shocks

Synchrotron Polarization Radiative Transfer: Relativistic Thermal Electron Contribution

The polarization-angle flip in GRB prompt emission

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