Monte Carlo radiation transfer simulations of photospheric emission in long-duration Gamma-Ray Bursts

TL;DR

This paper introduces MCRaT, a Monte Carlo radiation transfer code, to simulate photospheric emission in long-duration gamma-ray bursts, comparing results with observations to evaluate the model's viability.

Contribution

The paper presents a new Monte Carlo radiation transfer code, MCRaT, for modeling photospheric emission in gamma-ray bursts and applies it to hydrodynamic simulations.

Findings

Photospheric emission can explain the prompt phase peak frequency.

Challenges remain in reproducing the flat spectrum below the peak.

Results depend on hydrodynamics and radiation transfer assumptions.

Abstract

We present MCRaT, a Monte Carlo Radiation Transfer code for self-consistently computing the light curves and spectra of the photospheric emission from relativistic, unmagnetized jets. We apply MCRaT to a relativistic hydrodynamic simulation of a long duration gamma-ray burst jet, and present the resulting light-curves and time-dependent spectra for observers at various angles from the jet axis. We compare our results to observational results and find that photospheric emission is a viable model to explain the prompt phase of long-duration gamma-ray bursts at the peak frequency and above, but faces challenges in reproducing the flat spectrum below the peak frequency. We finally discuss possible limitations of these results both in terms of the hydrodynamics and the radiation transfer and how these limitations could affect the conclusions that we present.