Program: GN-2020B-DD-104

Gamma-ray bursts (GRBs) are among the brightest and most energetic events in the universe. Their duration and hardness distribution has two modes, now understood to reflect (at least) two different central engines. Long, soft GRBs are known to be powered by the collapse of massive stars because these bursts are accompanied by Type Ic broad-line supernovae. Short, hard GRBs are powered by neutron star binary mergers of the kind that produced LIGO/Virgo GW170817. Yet these two observational classes blend together, and it can be difficult to interpret some GRBs based on their prompt emission alone. Bursts detected by Swift are well studied because with their accurate hard X-ray localizations it is relatively easy to pinpoint their host galaxies, measure their redshifts, and observe their panchromatic afterglows. However, both Fermi GRBs and LIGO/Virgo GW bursts are much harder to study in multiple wavelengths due to their position uncertainties of tens to thousands of square degrees. For the past several years, our team has been conducting a target of opportunity campaign with the Zwicky Transient Facility synoptic survey to track down the optical counterparts of Fermi short GRBs and GW mergers. We recently detected the afterglow of GRB 200826A. Although initially classified as a short GRB based on its duration, it is more consistent with a long, soft GRB based on its peak energy or hardness. It is an unusual burst either way: as a short GRB, it is exceptionally soft, as a long GRB, it is exceptionally short and somewhat faint. A long GRB interpretation makes an observationally testable prediction: an energetic core-collapse supernova (a “hypernova”) should rise and peak about 30 days after the burst. We seek deep optical imaging of the site of the afterglow in order to rule out or detect a supernova, and if detected, measure its bolometric and physical properties.