Studies of the environments of short-duration gamma-ray bursts (GRBs) from sub-kpc to galactic scales have provided several lines of indirect observational evidence that short GRBs originate from the mergers of compact object binaries (neutron stars and/or black holes; NS-NS/NS-BH). A fundamental prediction of NS-NS/NS-BH mergers is natal kicks imparted to the systems; thus the locations of short GRBs with respect to their hosts have served as the most crucial diagnostic in solving the progenitor question. One key result that has emerged from these studies is the discovery of a subset of short GRBs which lack coincident galaxies to deep optical and near-IR limits (termed "host-less" bursts). These events either originate from faint underlying low-luminosity or high redshift hosts, or originate from galaxies at large separations of tens to hundreds of kpc (indicative of large kicks). Here, we propose to use HST to obtain deep imaging of six "host-less" short GRBs which have deep ground-based optical limits of >25-26 mag, necessitating the sensitivity of HST. These observations will uncover or place meaningful limits on coincident hosts, providing vital constraints on the true spatial distribution of short GRBs, the fraction of highly-kicked mergers which occur far from their hosts, and will directly inform population synthesis models of compact object mergers, which at present rely on poorly constrained distributions of kick velocities and delay times. Our proposed WFC3/F110W observations will double the sample of host-less bursts, and are tailored to locate or rule out underlying hosts to a significantly greater depth and redshift than is possible from the ground.
|Effective start/end date||11/1/17 → 10/31/19|
- Space Telescope Science Institute (HST-GO-14685.007-A AMD 2// NAS5-26555)
- National Aeronautics and Space Administration (HST-GO-14685.007-A AMD 2// NAS5-26555)