Time-averaging Polarimetric and Spectral Properties of Gamma-Ray Bursts

TL;DR

This study analyzes polarimetric and spectral data from 27 gamma-ray bursts to infer jet compositions, revealing that most are Poynting-flux-dominated with higher polarization, and suggesting photosphere emission as a possible mechanism.

Contribution

It introduces a joint analysis of polarization and spectral properties of GRBs, classifies jet types, and models magnetic field configurations to understand radiation mechanisms.

Findings

62% of GRBs are Poynting-flux-dominated

10 GRBs classified as hybrid-dominated with higher polarization

No gamma-ray bursts identified as kinetic-energy-dominated

Abstract

The composition and radiation mechanism of gamma-ray bursts (GRBs) within jets continue to be hotly debated. Investigating the joint polarimetric and spectral properties is crucial for understanding GRB composition and radiation mechanism. Various jet properties, such as ``kinetic-energy-dominated" (KED), ``Poynting-flux-dominated" (PFD), and ``hybrid-dominated" (HD) relativistic outflows, have been inferred from observed GRB spectra, with expectations of differing polarization levels among them. In this study, we analyzed a sample of 27 GRBs detected by the Gamma-ray Burst Monitor on board the NASA Fermi Gamma-ray Space Telescope, focusing on 26 bursts with significant polarization measurements. Our analysis revealed that 16 bursts (62\%) were predominantly associated with the ``PFD'' jet type, while 10 bursts (38\%) were classified as HD, implying that photosphere emission may also be a possible mechanism powering the high levels of polarization. Notably, no bursts were identified as KED-type. We found distinct polarization properties, with HD-type bursts exhibiting consistently higher polarization levels than PFD-type bursts. We proposed models incorporating ordered and random magnetic field configurations specific to hybrid jets.