Progenitors of Low-redshift Gamma-Ray Bursts

Abstract

The bimodal distribution of the observed duration of gamma-ray bursts (GRBs) has led to the identification of two distinct progenitors; compact star mergers, comprising either two neutron stars (NSs) or an NS and a black hole, for short GRBs (SGRBs), and the so-called collapsars for long GRBs (LGRBs). It is therefore expected that formation rate (FR) of LGRBs should be similar to the cosmic star formation rate (SFR), while that of SGRBs to be delayed relative to the SFR. The localization of some LGRBs in and around the star-forming regions of host galaxies and some SGRBs away from such regions support this expectation. Another distinct feature of SGRBs is their association with gravitational-wave (GW) sources and kilonovae. However, several independent investigations of the FRs of long and short bursts, using the Efron–Petrosian non-parametric method, have shown the presence of a mild luminosity evolution, and an LGRB FR that is significantly larger than SFR at low redshift, and similar to the FR of SGRBs. In addition, the recent discovery of association of two low-redshift LGRB 211211A and LGRB 230307A with a kilonova cast doubt about their collapsar origin. In this Letter we review these results and show that our results predict that about 60% ± 5% of LGRBs with redshift less than 2 could have compact star merger as progenitors increasing the expected rate of the GW sources and kilonovae significantly. The remaining 40% ± 5% have collapsars as progenitors, with some having associated supernovae.

Gamma-Ray Bursts as Distance Indicators by a Statistical Learning Approach

“…Our results mirror similar deviations in the FRs of LGRBs found by 2021) also arrived at a similar conclusion regarding SGRBs at low redshifts even though the delayed SFR has been accounted for. Our primary conclusion, which aligns with findings reached by Petrosian & Dainotti (2024), is that the population of LGRBs at low redshift includes a component of compact merger progenitors, similar to the SGRBs. A different explanation for the excess of GRBs at low redshift, originally proposed by Yoon et al (2006), is related to the increase in metallicity with cosmic time, which prevents a larger fraction of massive stars from producing GRBs.…”

“…However, these results depend on the claim of the completeness of the sample of the GRB hosts, which can be debated. Another relevant possibility is that the low-z GRBs have the same noncollapsar origin (Petrosian & Dainotti 2024) of the SGRBs. The resulting LF and density-rate evolutions are consistent with the ones in the literature and are also consistent between the ones derived from z obs and z pred .…”