Mini-Supernovae from Outflows from Accretion Disks formed by Compact
Object Mergers and Accretion-Induced Collapse

Brian Metzger
(UC Berkeley)


Massive, compact accretion disks are thought to form in a number of astrophysical events, including (1) the merger of a neutron star (NS) with a black hole (BH) or with another NS, and (2) following the accretion-induced collapse (AIC) of a white dwarf to a NS.  These disks, termed 'hyper-accreting' due to their large accretion rates of up to several solar masses per second, may power the relativistic jets that produce gamma-ray bursts.  I will present time-dependent calculations of the evolution of hyper-accreting disks as they accrete onto the central NS or BH and spread outwards in radius.  I will show that a generic consequence of the disk's evolution is that powerful outflows are driven from the disk at late times, which synthesize heavy radioactive elements as they expand into space.  I will discuss the nucleosynthetic yields of both NS-NS/NS-BH mergers and AIC and their resulting observable consequences.  Outflows from NS-NS/NS-BH accretion disks are generically neutron-rich and represent a new site for very heavy element nucleosynthesis.  By contrast, AIC outflows produce a significant amount of Ni 56, whose decay will power an optical transient that may be detectable with upcoming optical transient surveys or as an electromagnetic counterpart to a gravitational wave signal.  I will conclude by speculating that AIC may explain some of the unusual sub-luminous Type I supernovae that have been discovered recently.