Are Long Gamma-Ray Bursts Progenitors to Merging Binary Black Holes?

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 G. Ghirlanda & R. Salvaterra and the BBH merger rate inferred by LIGO-Virgo-KAGRA 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 $\alpha ={-0.96}_{-0.76}^{+0.64}$ (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}_{-2}^{+10} \% $ of LGRBs may evolve into merging BBHs. We also consider the possibility that LGRBs only produce BBH systems with large aligned spins (with effective inspiral spin χ _eff > 0.2). In this case, we find $f=0.{3}_{-0.2}^{+1.0} \% $ and the delay time distribution favors the steepest power-law slopes we consider ( α = −2). We argue that asynchronous observations of LGRBs and GWs provide a powerful multimessenger probe of black hole life cycles across cosmic history.

Keywords

• Astrophysical black holes
• Massive stars
• Gamma-ray bursts
• Gravitational wave astronomy
• Stellar mass black holes