Neutron star mergers are confirmed sites of r-process nucleosynthesis, observationally identified by their kilonovae. In particular, the study of short gamma-ray bursts (SGRBs), which span z~0.1-2, are a promising avenue to uncover kilonovae. Monitoring the temporal and color evolution of SGRB-kilonovae provides quantifiable estimates of their ejecta masses and compositions, of interest to assessing the contribution of such mergers to the universe's heavy element budget. In particular, the identification of nearby (z&lt;0.1) kilonovae provide great distinguishing power. Recently, GRB 211211A was discovered in likely association with a galaxy at 350 Mpc (z=0.076). At this distance, the detection and temporal behavior of an associated NIR transient is fully consistent with a kilonova. If the distance is confirmed, this would make GRB 211211A the most nearby such event beyond the multi-messenger GW170817. We propose 2 orbits of HST imaging to secure the nearby origin of GRB 211211A by placing constraints on an underlying, unseen galaxy. Current ground-based observations have reached their limits, and cannot rule out the full range of known host galaxy luminosities and redshifts. If an underlying galaxy is detected from a higher-redshift origin, the NIR transient would be equally exciting, outshining any known kilonova or supernova to date. Thus, our science goals regarding the HST data are two-fold:  Determine the origin of GRB 211211A, by either detecting an underlying, faint host galaxy, or by placing a limit on a coincident host (strengthening the case for the bright galaxy as the host at dL = 350 Mpc).  Perform modeling of the host galaxy to characterize and compare its properties to the short GRB host galaxy population.
|Effective start/end date||6/1/22 → 5/31/25|
- Space Telescope Science Institute (HST-GO-16923.005-A//NAS5- 26555)
- National Aeronautics and Space Administration (HST-GO-16923.005-A//NAS5- 26555)
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