Confronting GRB prompt emission with a model for subphotospheric dissipation

TL;DR

This paper introduces DREAM, a new model for GRB prompt emission based on subphotospheric dissipation, successfully fitting diverse Fermi GRB spectra and suggesting optical depth influences spectral shape.

Contribution

The paper presents a physically motivated photospheric emission model with dissipation, implemented as a table model for XSPEC, capable of fitting various GRB spectra.

Findings

DREAM model fits different GRB spectral types including Band and double-peaked spectra.

Spectral differences are linked to optical depth at the dissipation site.

The model suggests a common origin for different GRB spectral shapes.

Abstract

The origin of the prompt emission in gamma-ray bursts (GRBs) is still an unsolved problem and several different mechanisms have been suggested. Here we fit Fermi GRB data with a photospheric emission model which includes dissipation of the jet kinetic energy below the photosphere. The resulting spectra are dominated by Comptonization and contain no significant contribution from synchrotron radiation. In order to fit to the data we span a physically motivated part of the model's parameter space and create DREAM ($\textit{Dissipation with Radiative Emission as A table Model}$), a table model for ${\scriptsize XSPEC}$. We show that this model can describe different kinds of GRB spectra, including GRB 090618, representing a typical Band function spectrum, and GRB 100724B, illustrating a double peaked spectrum, previously fitted with a Band+blackbody model, suggesting they originate from a similar scenario. We suggest that the main difference between these two types of bursts is the optical depth at the dissipation site.