Explosive events seen at extragalactic distances mark the end-state of violent and catastrophic physical processes. Most supernovae and gamma-ray bursts (GRBs), in particular, are thought to herald the death of massive stars and the birth of solar-mass black holes. A minority fraction of GRBs, however, have been circumstantially associated with the merger of degenerate systems (such as black holes and neutron stars). These short-duration bursts are rare and difficult to localize, with only about 2 dozen studied to any degree of detail to date. We believe that we have finally discovered, in the last few days, one of the tell-tale signatures of degenerate merger products --- a "mini-supernova" from the non-relativistic ejecta left over after merger. If true, this long-theorized phenomenon would be an entirely new sort of explosion in the universe. In several rapidly executed visits, HST, coupled with a recently approved Chandra DD proposal to search for underlying afterglow, could make a substantial contribution to our understanding of this phenomena by honing the physical parameters of the event and helping to rule out alternatives. If we are correct in our hypothesis, we have found the first clear cut observational signature in the electromagnetic spectrum of what are expected to the be the dominant sources of gravitational waves for advanced LIGO.

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