Very high efficiency photospheric emission in long duration gamma-ray bursts

TL;DR

This study uses numerical simulations to show that long-duration gamma-ray burst jets efficiently convert their energy into radiation at the photosphere, explaining their high radiative efficiency.

Contribution

It demonstrates that photospheric emission is highly efficient in long GRB jets and highlights the role of jet-star interactions beyond the stellar surface.

Findings

Photospheric emission converts over half of jet energy into radiation.

Bright photospheres are common in jets from massive progenitors.

Jet-star interactions influence jet evolution beyond the stellar surface.

Abstract

We numerically analyze the evolution of a long-duration gamma-ray burst jet as it leaves the progenitor star and propagates to the photospheric radius, where radiation can be released. We find that the interaction of the relativistic material with the progenitor star has influences well beyond the stellar surface. Tangential collimation shocks are observed throughout the jet evolution, out to about 100 stellar radii, which is the whole range of our simulation. We find that the jet is internally hot at the photospheric radius and we compute the photospheric emission. The photosphere is a very efficient radiator, capable of converting more than half of the total energy of the jet into radiation. We show that bright photospheres are a common feature of jets born inside massive progenitor stars and that this effect can explain the high radiative efficiency observed in long-duration bursts.