Forward-Modeling of Double Neutron Stars: Insights from Highly-Offset Short Gamma-ray Bursts. (arXiv:1910.03598v1 [astro-ph.HE])

Forward-Modeling of Double Neutron Stars: Insights from Highly-Offset Short Gamma-ray Bursts. (arXiv:1910.03598v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Zevin_M/0/1/0/all/0/1">Michael Zevin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kelley_L/0/1/0/all/0/1">Luke Zoltan Kelley</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nugent_A/0/1/0/all/0/1">Anya Nugent</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fong_W/0/1/0/all/0/1">Wen-fai Fong</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Berry_C/0/1/0/all/0/1">Christopher P. L. Berry</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kalogera_V/0/1/0/all/0/1">Vicky Kalogera</a>

We perform a detailed analysis of two well-localized, highly-offset short
gamma-ray bursts — GRB070809 and GRB090515 — investigating the prior
kinematic evolution of their progenitors from compact object formation until
merger. Calibrated to observations of their most probable 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 $gtrsim,250~mathrm{km,s}^{-1}$. For massive and
quiescent hosts, we see $sim,20%$ of mergers occur at $gtrsim,5$ effective
radii from their hosts. Though the offset of GRB070809 is explainable with
small supernova natal kicks, our modeling suggests that the second-born neutron
star in the GRB090515 progenitor system received a natal kick of
$gtrsim,200~mathrm{km,s}^{-1}$ at the $98%$ credible level. 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.

We perform a detailed analysis of two well-localized, highly-offset short
gamma-ray bursts — GRB070809 and GRB090515 — investigating the prior
kinematic evolution of their progenitors from compact object formation until
merger. Calibrated to observations of their most probable 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 $gtrsim,250~mathrm{km,s}^{-1}$. For massive and
quiescent hosts, we see $sim,20%$ of mergers occur at $gtrsim,5$ effective
radii from their hosts. Though the offset of GRB070809 is explainable with
small supernova natal kicks, our modeling suggests that the second-born neutron
star in the GRB090515 progenitor system received a natal kick of
$gtrsim,200~mathrm{km,s}^{-1}$ at the $98%$ credible level. 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.

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