Gamma-ray bursts from magnetized collisionally-heated jets

TL;DR

This paper models gamma-ray burst jets with neutron components, showing that collisional heating produces spectra consistent with observations, and explores how magnetic fields influence the spectrum's shape and features.

Contribution

The study extends previous collisional heating models by incorporating magnetic fields, revealing their effects on GRB spectra and confirming the mechanism's ability to produce observed spectral features.

Findings

Spectrum peak remains near 1 MeV across magnetization levels.

Softening of the low-energy spectrum with increasing magnetic field.

High-energy emission extends above GeV, matching Fermi/LAT observations.

Abstract

Jets producing gamma-ray bursts (GRBs) are likely to carry a neutron component that drifts with respect to the proton component. The neutron-proton collisions strongly heat the jet and generate electron-positron pairs. We investigate radiation produced by this heating using a new numerical code. Our results confirm the recent claim that collisional heating generates the observed Band-type spectrum of GRBs. We extend the model to study the effects of magnetic fields on the emitted spectrum. We find that the spectrum peak remains near 1 MeV for the entire range of the magnetization parameter $0<\epsilon_B<2$ that is explored in our simulations. The low-energy part of the spectrum softens with increasing $\epsilon_B$, and a visible soft excess appears in the keV band. The high-energy part of the spectrum extends well above the GeV range and can contribute to the prompt emission observed by Fermi/LAT. Overall, the radiation spectrum created by the collisional mechanism appears to agree with observations, with no fine-tuning of parameters.