Population-synthesis predictions for where merging neutron-star binaries occur relative to their host galaxies, and what burst offsets imply for the merger progenitor model.
A contributed talk in the “Neutron Stars & Pulsars” oral session; the work was published as Bloom, Sigurdsson & Pols 1999, MNRAS 305, 763 (astro-ph/9805222).
AAS abstract 113.04, with S. Sigurdsson and O. Pols.
We find the distribution of merger times, spatial velocities, and subsequent radial offsets of coalescing NSs in various galactic potentials. Due to large asymmetric kicks introduced during the two supernovae, bound NS pairs exhibit an anticorrelation of vsys and merger time τ. As such only a small fraction of coalescing NSs (≤ 1 percent), even in shallow galactic potentials (L ≤ 0.1 L*), escape to distances beyond 20 kpc from the galactic centre. This indicates that most NS coalescences will occur inside their hosts, with only a small fraction undergoing coalescence at large projected separations. In addition, we find that the spatial distribution of coalescing neutron star binaries is consistent with the close spatial association of the afterglows of gamma-ray bursts GRB 970228 and GRB 970508 with underluminous galaxies.