Probing the progenitors of spinning binary black-hole mergers with long gamma-ray bursts

Abstract

Long-duration gamma-ray bursts are thought to be associated with the core-collapse of massive, rapidly spinning stars and the formation of black holes. However, efficient angular momentum transport in stellar interiors, currently supported by asteroseismic and gravitational-wave constraints, leads to predominantly slowly-spinning stellar cores. Here, we report on binary stellar evolution and population synthesis calculations, showing that tidal interactions in close binaries not only can explain the observed subpopulation of spinning, merging binary black holes but also lead to long gamma-ray bursts at the time of black-hole formation. Given our model calibration against the distribution of isotropic-equivalent energies of luminous long gamma-ray bursts, we find that ≈10% of the GWTC-2 reported binary black holes had a luminous long gamma-ray burst associated with their formation, with GW190517 and GW190719 having a probability of ≈85% and ≈60%, respectively, being among them. Moreover, given an assumption about their average beaming fraction, our model predicts the rate density of long gamma-ray bursts, as a function of redshift, originating from this channel. For a constant beaming fraction fB ∼ 0.05 our model predicts a rate density comparable to the observed one, throughout the redshift range, while, at redshift z ∈ [0, 2.5], a tentative comparison with the metallicity distribution of observed LGRB host galaxies implies that between 20% to 85% of the observed long gamma-ray bursts may originate from progenitors of merging binary black holes. The proposed link between a potentially significant fraction of observed, luminous long gamma-ray bursts and the progenitors of spinning binary black-hole mergers allows us to probe the latter well outside the horizon of current-generation gravitational wave observatories, and out to cosmological distances.

Are binary black hole mergers and long gamma-ray bursts drawn from the same black hole population?

“…• These three factors, which all go in the same direction, lead to a ratio of ∼ 100 between the long GRB rate used by Bavera et al (2022) and the one we use. This explains why we find that at most a small fraction of LGRBs could be associated to BBH mergers, while Bavera et al (2022) propose to associate all long GRBs with the sub-population of BBH mergers with nonzero spin. In the rest of this discussion we consider that our LGRB models (including the beaming factor) are realistic, and we discuss our findings in this context.…”

“…The core angular momentum has been transferred to the stellar envelope which has been ejected. This is the indication of an efficient transport of angular momentum in the progenitors of BBH mergers and possibly in most massive stars (Olejak & Belczynski 2021;Bavera et al 2022;Fuller & Lu 2022). If this scenario is correct, LGRBs, which require stellar cores with a large angular momentum at BH creation, cannot be emitted by single massive stars, nor by massive stars in wide binary systems.…”

“…• The SHOALS survey used as a reference for the LGRBs distribution in Bavera et al (2022) gives a local rate of observed GRBs ∼ 0.2 Gpc −3 yr −1 , while the ones used in this papers are larger, and closer to 1 Gpc −3 yr −1 .…”

“…• The population of BH progenitors generated by Bavera et al (2022) for the production of LGRBs is based on a value close to the upper limit of the local rate measured by LVC, ρ(z 0 = 0) = 38.3 Gpc −3 yr −1 . We have taken the logarithmic mean of the upper-and lower-limits (ρ(z 0 = 0.2) = 28 Gpc −3 yr −1 ), which is smaller.…”

“…In this model, the population of LGRBs and BBHs (or at least a sub-sample of the latter) would therefore share common progenitors. Bavera et al (2022) have recently published a study using binary stellar evolution and population synthesis calculations to explain the subpopulation of spinning merging BBHs and the emission of LGRBs at the BH formation. They reach the conclusion that the progenitors of fastspinning BBH mergers, formed via isolated binary evolution, are likely a major contribution to the observed rate of luminous LGRBs.…”