Are long gamma-ray bursts progenitors to merging binary black holes?

TL;DR

This study compares the rate and delay time distribution of long gamma-ray bursts (LGRBs) and binary black hole (BBH) mergers, suggesting a potential link in their formation history but limited contribution of LGRBs to BBH mergers.

Contribution

It introduces the use of LGRB rates to infer BBH progenitor delay times and estimates the fraction of LGRBs that evolve into BBH mergers, providing new insights into their connection.

Findings

Delay time distribution follows a power law with a minimum delay of 10 Myr.

At most 4% of LGRBs evolve into BBH mergers.

LGRBs with large aligned spins have a lower contribution to BBH mergers.

Abstract

The distribution of delay times between the formation of binary black hole (BBH) progenitors and their gravitational-wave (GW) merger provides important clues about their unknown formation histories. When inferring the delay time distribution, it is typically assumed that BBH progenitor formation traces the star formation rate (SFR). In this work, we consider the rate of long gamma-ray bursts (LGRBs) instead of the SFR. LGRBs are thought to correspond to the formation of (possibly spinning) black holes, and may therefore be related to the BBH progenitor population. By comparing the redshift evolution of the LGRB rate as inferred by Ghirlanda & Salvaterra (2022) and the BBH merger rate inferred by LIGO-Virgo-KAGRA (LVK) observations, we find that the delay time distribution between LGRBs and BBH mergers is well-described by a power law with minimum delay time $10$ Myr and slope $\alpha ={-0.96}^{+0.64}_{-0.76}$ (90% credibility). This matches theoretical expectations for the BBH delay time distribution, which in turn lends support to the hypothesis that LGRBs trace BBH progenitor formation. However, comparing the absolute rates of these two populations, we find that at most $f = {4}^{+10}_{-2}\%$ of LGRBs may evolve into merging BBH. We also consider the possibility that LGRBs only produce BBH systems with large aligned spins (with effective inspiral spin $\chi_\mathrm{eff} > 0.2$). In this case, we find $f = 0.3^{+1.0}_{-0.2}\%$ and the delay time distribution favors the steepest power-law slopes we consider ($\alpha = -2$). We argue that asynchronous observations of LGRBs and GWs provide a powerful multimessenger probe of black hole lifecycles across cosmic history.