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

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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.