Kilonova and progenitor properties of merger-driven gamma-ray bursts

Context. Gamma-ray burst (GRB) prompt and afterglow emission, as well as kilonova (KN) emission, are the expected electromagnetic (EM) counterparts of binary neutron star (BNS) and neutron star-black hole (NSBH) mergers. Only one BNS merger (GW170817) detected on the basis of gravitational waves (GWs) has a confirmed association with EM counterparts. Without a GW signal, the ejecta parameters from a KN can be used to infer the progenitor properties. Aims. We aim to infer the KN ejecta parameters and the progenitor properties by modeling merger-driven GRBs with a claim of KN, good data, and robust redshift measurements. Methods. We modeled the afterglow and KN, performing a Bayesian analysis, within the Nuclear physics and Multi-Messenger Astrophysics ( NMMA ) framework. The KN emission is modeled with the radiative transfer code POSSIS and for the afterglow, we used the afterglowpy library. In contrast to previous approaches, our methodology simultaneously models both the afterglow and KN. Results. We find that all GRBs in our sample have a KN, but we were unable to confirm or exclude its presence in GRB 150101B. A BNS progenitor is favored for GRB 160821B, GRB 170817A/AT2017gfo, GRB 211211A, and GRB 230307A. For GRB 150101B and GRB 191019A, we found a slight preference for the NSBH scenario; however, a BNS is also a viable possibility. For the KN emission, we see that the median wind mass ⟨ M wind ⟩ = 0.27 −0.019 +0.046 M ⊙ is higher than the dynamical ⟨ M dyn ⟩ = 0.012 −0.006 +0.012 M ⊙ . Finally, we find that M wind and the collimation-corrected energy of the jet can be expressed as log( M wind ) = − 20.23 + 0.38 log( E 0, J ). We confirm the results of numerical simulations, demonstrating that the mass-weighted tidal deformability, ∼Λ, increases along with a decrease in the chirp mass, ℳ Chirp . Conclusions. Our results exemplify and reinforce that EM modeling is the only feasible pathway to investigate binary mergers in absence of GW observations. In this work, we present for the first time the binary progenitor properties of a sizable sample of merger-driven GRBs.