Magnetically and Baryonically Dominated Photospheric Gamma-Ray Burst Model Fits to Fermi LAT Observations

TL;DR

This paper models gamma-ray bursts with photospheric and external shock regions, fitting Fermi LAT observations to explore magnetically and baryonically dominated regimes, and compares their effectiveness in explaining observed spectra.

Contribution

It introduces a parametrized model for GRB dynamics covering magnetic and baryonic dominance, fitting Fermi LAT data to evaluate their spectral predictions.

Findings

Both models fit the observed spectra well.

Time-resolved spectra are consistent with the models.

Parameters suggest different dominance regimes in GRB emissions.

Abstract

We consider gamma-ray burst models where the radiation is dominated by a photospheric region providing the MeV Band spectrum, and an external shock region responsible for the GeV radiation via inverse Compton scattering. We parametrize the initial dynamics through an acceleration law Gamma \propto r^\mu, with \mu between 1/3 and 1 to represent the range between an extreme magnetically dominated and a baryonically dominated regime. We compare these models to several bright Fermi LAT bursts, and show that both the time integrated and the time resolved spectra, where available, can be well described by these models. We discuss the parameters which result from these fits, and discuss the relative merits and shortcomings of the two models.