RHESSI Tests of Quasi-Thermal Gamma-Ray Burst Spectral Models

TL;DR

This study tests quasi-thermal spectral models against broad-band gamma-ray data from RHESSI for nine bright gamma-ray bursts, finding that these models fit poorly compared to the phenomenological Band function, with fit parameters highly band-dependent.

Contribution

It provides a comprehensive evaluation of quasi-thermal models using broad-band data, highlighting their limitations relative to the Band function in describing GRB spectra.

Findings

Quasi-thermal models fit poorly compared to the Band function.

Fit parameters for simple models depend on the energy band.

More complex nonthermal models do not improve fit robustness.

Abstract

Prompt gamma-ray burst spectra evolve on short time scales, suggesting that time-resolved spectral fits may help diagnose the still unknown prompt emission mechanism. We use broad-band gamma-ray data from the RHESSI spacecraft to test quasi-thermal models with high signal-to-noise time-resolved spectra of nine bright gamma-ray bursts. In contrast to results reported in more narrow energy bands, the quality of the fits of quasi-thermal models is poor in relation to fits of the phenomenological Band function. Moreover, the best-fit parameters for the simplest quasi-thermal model, a black body plus a nonthermal power law, show significant dependence on the fit band. Models that replace the power law with more complicated nonthermal functions are not robust for the data considered here and decrease the physical relevance of the fit black body.