Forward Modeling of Double Neutron Stars: Insights from Highly Offset Short Gamma-Ray Bursts

• Published in: The Astrophysical journal Vol. 904; no. 2; pp. 190 - 202
• Main Authors: Zevin, Michael, Kelley, Luke Zoltan, Nugent, Anya, Fong, Wen-fai, Berry, Christopher P. L., Kalogera, Vicky
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.12.2020; IOP Publishing
• Subjects: Astronomical models; Astrophysics; Binary stars; Compact binary stars; Galactic evolution; Galactic models; Galaxies; Galaxy evolution; Gamma ray bursts; Gamma rays; Kinematics; Modelling; Neutron stars; Offsets; Progenitors (astrophysics); Star & galaxy formation; Star formation; Stellar evolution; Stellar mass; Supernova; Supernova dynamics; Supernovae; Time dependence; Tracers
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/abc266

We present a detailed analysis of two well-localized, highly offset short gamma-ray bursts-GRB 070809 and GRB 090515-investigating the kinematic evolution of their progenitors from compact object formation until merger. Calibrating to observations of their most probable host galaxies, we construct semi-analytic galactic models that account for star formation history and galaxy growth over time. We pair detailed kinematic evolution with compact binary population modeling to infer viable post-supernova velocities and inspiral times. By populating binary tracers according to the star formation history of the host and kinematically evolving their post-supernova trajectories through the time-dependent galactic potential, we find that systems matching the observed offsets of the bursts require post-supernova systemic velocities of hundreds of kilometers per second. Marginalizing over uncertainties in the stellar mass-halo mass relation, we find that the second-born neutron star in the GRB 070809 and GRB 090515 progenitor systems received a natal kick of at the and credible levels, respectively. Applying our analysis to the full catalog of localized short gamma-ray bursts will provide unique constraints on their progenitors and help unravel the selection effects inherent to observing transients that are highly offset with respect to their hosts.