Ultra Long Gamma-Ray Bursts from the collapse of Blue Super Giant stars: an end-to-end simulation

TL;DR

This study uses end-to-end simulations to evaluate whether blue super giant stars can produce ultra-long gamma-ray bursts, demonstrating that jets can emerge and produce light curves similar to observed ULGRBs.

Contribution

First comprehensive simulation of BSG stars as ULGRB progenitors, linking stellar evolution, accretion, and jet emergence to observed burst durations.

Findings

Jets can successfully emerge from BSG stars during collapse.

Simulated light curves match observed ULGRB durations.

Jet emergence depends on viewing angle.

Abstract

Ultra-long gamma ray bursts (ULGRBs) are a distinct class of GRBs characterized by durations of several thousands of seconds, about two orders of magnitude longer than those of standard long GRBs (LGRBs). The driving engine of these events has not been uncovered yet, and ideas range from magnetars, to tidal disruption events, to extended massive stars, such as blue super giants (BSG). BSGs, a possible endpoint of stellar evolution, are attractive for the relatively long free-fall times of their envelopes, allowing accretion to power a long-lasting central engine. At the same time, their large radial extension poses a challenge to the emergence of a jet. Here we perform an end-to-end simulation aimed at assessing the viability of BSGs as ULGRB progenitors. The evolution to core collapse of a BSG star model is calculated with the MESA code. We then compute the accretion rate for the fraction of envelope material with enough angular momentum to circularize and form an accretion disk, and input the corresponding power into a jet which we evolve through the star envelope with the FLASH code. Our simulation shows that the jet can emerge, and the resulting light curves resemble those observed in ULGRBs, with durations $T_{90}$ ranging from $\approx$4000~s to $\approx10^4$ s depending on the viewing angle.