Supercollapsars and their X-ray Bursts

TL;DR

This paper explores the potential observability of high-energy X-ray bursts from supermassive collapsars in the early universe, highlighting their energetic jets, long durations, and spectral characteristics.

Contribution

It introduces the concept of supercollapsars as sources of observable X-ray bursts, analyzing their jet power, duration, spectrum, and potential detection rates.

Findings

Jets can reach energies of up to 10^{54} erg.

Burst durations can last around 10^4 seconds.

Expected detection rate is several tens per year across the sky.

Abstract

The very first stars in the Universe can be very massive, up to $10^3M_\odot$. If born in large numbers, such massive stars can have strong impact on the subsequent star formation, producing strong ionising radiation and contaminating the primordial gas with heavy elements. They would leave behind massive black holes that could act as seeds for growing supermassive black holes of active galactic nuclei. Given the anticipated fast rotation, such stars would end their live as supermassive collapsars and drive powerful magnetically-dominated jets. In this letter we investigate the possibility of observing the bursts of high-energy emission similar to the Long Gamma Ray Bursts associated with normal collapsars. We show that during the collapse of supercollapsars, the Blandford-Znajek mechanism can produce jets as powerful as few$\times10^{52}$erg/s and release up to $10^{54}$erg of the black hole rotational energy. Due to the higher intrinsic time scale and higher redshift the initial bright phase of the burst can last for about $10^4$ seconds, whereas the central engine would remain active for about one day. Due to the high redshift the burst spectrum is expected to be soft, with the spectral energy distribution peaking at around 20-30keV. The peak total flux density is relatively low, $10^{-7}{erg} {cm}^{-2} {s}^{-1}$, but not prohibitive. If one supercollapsar is produced per every mini-halo of dark matter arising from the 3-$\sigma$ cosmological fluctuations then the whole sky frequency of such bursts could reach several tens per year.