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

Sharma, V.; Iyyani, Shabnam; Bhattacharya, Dipankar; Chattopadhyay, Tanmoy; Vadawale, S.; Bhalerao, V.

doi:10.1093/mnras/staa570

Cited by 13 publications

(10 citation statements)

References 123 publications

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“…Finally, we only see signs of an evolving PA inside of single pulses. We do not see any signs of evolving polarization angles outside of individual pulses or in overlapping pulses, such as those reported for example by GAP for GRB 100826A (Yonetoku et al 2011) or by the AstroSat CZT-Imager collaboration for GRB 160821A (which consists of a single emission episode but with several overlapping pulses) and 160325A (Sharma et al 2019a(Sharma et al , 2020.…”

Section: Resultssupporting

confidence: 53%

The POLAR gamma-ray burst polarization catalog

Kole

Angelis²,

Berlato³

et al. 2020

A&A

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Context. Despite over 50 years of research, many open questions remain about the origin and nature of gamma-ray bursts (GRBs). Linear polarization measurements of the prompt emission of these extreme phenomena have long been thought to be key to answering a range of these questions. The POLAR detector was designed to produce the first set of detailed and reliable linear polarization measurements in the 50 − 500 keV energy range. During late 2016 and early 2017, POLAR detected a total of 55 GRBs. The analysis results of 5 of these GRBs have been reported, and were found to be consistent with a low or unpolarized flux. However, previous reports by other collaborations found high levels of linear polarization, including some as high as 90%. Aims. We study the linear polarization for the 14 GRBs observed by POLAR for which statistically robust inferences are possible. Additionally, time-resolved polarization studies are performed on GRBs with sufficient apparent flux. Methods. A publicly available polarization analysis tool, developed within the Multi-Mission Maximum Likelihood framework (3ML), was used to produce statistically robust results. The method allows spectral and polarimetric data from POLAR to be combined with spectral data from the Fermi Gamma-ray Burst Monitor (Fermi-GBM) and the Neil Gehrels Swift Observatory (hereafter Swift) to jointly model the spectral and polarimetric parameters. Results. The time-integrated analysis finds all results to be compatible with low or zero polarization with the caveat that, when timeresolved analysis is possible within individual pulses, we observe moderate linear polarization with a rapidly changing polarization angle. Therefore, time-integrated polarization results, while pointing to lower polarization, are potentially an artifact of summing over the changing polarization signal and thus washing out the true moderate polarization. We therefore caution against overinterpretation of any time-integrated results inferred herein and encourage the community to wait for more detailed polarization measurements from forthcoming missions such as POLAR-2 and LEAP.

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Section: Resultssupporting

confidence: 53%

The POLAR gamma-ray burst polarization catalog

Kole

Angelis²,

Berlato³

et al. 2020

A&A

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“…The Cadmium Zinc Telluride Imager (CZTI) on board AstroSat reported high polarization for most of the 11 bright GRBs detected in the first year of its operation (Chattopadhyay et al 2019). Detailed spectropolarimetric analysis of some of these bright GRBs revealed time-and energy-dependent variation in polarization happening across the burst duration (Chand et al 2018(Chand et al , 2019Sharma et al 2019Sharma et al , 2020. Most importantly, we note that the detailed study of GRB 160821A showed a ∼90°flip in polarization angle occurring twice within a single broad emission pulse (Sharma et al 2019).…”

Section: Introductionmentioning

confidence: 81%

Hard X-Ray Polarization Catalog for a Five-year Sample of Gamma-Ray Bursts Using AstroSat CZT Imager

Chattopadhyay

Gupta

Iyyani

et al. 2022

ApJ

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The Cadmium Zinc Telluride Imager (CZTI) on board AstroSat has been regularly detecting gamma-ray bursts (GRBs) since its launch in 2015. Its sensitivity to polarization measurements at energies above 100 keV allows CZTI to attempt spectropolarimetric studies of GRBs. Here, we present the first catalog of GRB polarization measurements made by CZTI during its first five years of operation. This includes the time-integrated polarization measurements of the prompt emission of 20 GRBs in the energy range 100–600 keV. The sample includes the bright GRBs that were detected within an angle range of 0°–60° and 120°–180° where the instrument has useful polarization sensitivity and is less prone to systematics. We implement a few new modifications in the analysis to enhance the polarimetric sensitivity of the instrument. The majority of the GRBs in the sample are found to possess less/null polarization across the total bursts’ duration in contrast to a small fraction of five GRBs that exhibit high polarization. The low polarization across the bursts might be due either to the burst being intrinsically weakly polarized or to a varying polarization angle within the burst even when it is highly polarized. In comparison to POLAR measurements, CZTI has detected a larger number of cases with high polarization. This may be a consequence of the higher energy window of CZTI observations, which results in the sampling of a shorter duration of burst emissions than POLAR, thereby probing emissions with less temporal variation in polarization properties.

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“…Both the IBIS, GAP, and AstroSAT CZTI collaborations have reported an evolution of the PA over more complex GRBs consisting either of multiple separated pulses (100826A, 160325A) or overlapping pulses (041219A, 160821A) [220,225,226,230]. For both 100826A and 160821A the evolution is reported to be compatible with PA changes of 90 • .…”

Section: Time Resolved Measurementsmentioning

confidence: 76%