On the duration of long GRBs: effects of black hole spin

TL;DR

This paper explores how black hole spin influences the duration of long gamma-ray bursts within the collapsar model, highlighting the conditions under which different jet types and burst lengths occur based on progenitor star properties.

Contribution

It introduces a model linking black hole spin and accretion dynamics to GRB durations, providing a framework to predict burst lengths and jet types from progenitor characteristics.

Findings

Higher black hole spin can extend GRB duration.

Three jet types can originate from a single collapse event.

Progenitor star properties determine GRB length and jet nature.

Abstract

In the frame of the collapsar model for long gamma ray bursts (GRBs), we investigate the formation of a torus around a spinning BH and we check what rotational properties a progenitor star must have in order to sustain torus accretion over relatively long activity periods. We also study the time evolution of the BH spin parameter. We take into account the coupling between BH mass, its spin parameter and the critical specific angular momentum of accreting gas, needed for the torus to form. The large BH spin reduces the critical angular momentum which in turn can increase the GRB duration with respect to the Schwarzschild BH case. We quantify this effect and estimate the GRB durations in three cases: when a hyper accreting torus operates or a BH spins very fast or both. We show under what conditions a given progenitor star produces a burst that can last as short as several seconds and as long as several hundred of seconds. Our models indicate that it is possible for a single collapse to produce three kinds of jets: (1) a very short, lasting between a fraction of a second and a few seconds, 'precursor' jet, powered only by a hyper accreting torus before the BH spins up, (2) an 'early' jet, lasting several tens of seconds and powered by both hyper accretion and BH rotation, and (3) a 'late' jet, powered only by the spinning BH.