Many faces of accretion in gamma ray bursts

TL;DR

This paper explores the diverse accretion processes powering gamma-ray bursts, focusing on black hole formation, jet launching conditions, and the properties of collapsing stars as GRB progenitors.

Contribution

It provides new insights into the conditions necessary for variable jet launching and the impact of black hole spin and self-gravity on GRB production.

Findings

Black hole spin influences jet variability.

Conditions for bright gamma-ray transients are identified.

Accretion disk properties under extreme conditions are discussed.

Abstract

Accretion powers relativistic jets in GRBs, similarly to other jet sources. Black holes that are at heart of long GRBs, are formed as the end product of stellar evolution. At birth, some of the black holes must be very rapidly spinning, to be able to power the GRBS. In some cases, the black holes may be born without formation of a disk/jet engine, and then the star will collapse without an electromagnetic transient. In this proceeding, we discuss the conditions for launching variable jets from the magnetized disk in an arrested state. We also discuss properties of collapsing massive stars as progenitors of GRBs, and the conditions which must be satisfied for the star in order for the collapsar to produce a bright gamma-ray transient. We find that the black hole rotation is further affected by self-gravity of the collapsing matter. Finally, we comment on the properties of the accretion disk under extreme conditions of nuclear densities and temperatures, while it can contribute to the kilonova accompanying short GRBs.