Swift discoveries of new populations of extremely long duration high energy transient

Abstract

Recent observations with Swift have begun to uncover $\gamma$-ray transients whose total energies are comparable to those of gamma-ray bursts (GRB), but have a duration an order of magnitude or more longer than the bulk of the GRB population. Some are suggested to form a new population of ultra-long GRBs, with a mean duration around $10^4$s, while a further population with $\gamma-$ray durations $>10^5$ s may represent manifestations of relativistic outflows from stars shredded around massive black holes in tidal disruption flares (TDFs). Here I review the observations of these new classes of events, discuss progress towards identifying their progenitors and suggest how new observations may both hone our understanding of the outbursts, and allow them to be used as probes, that offer both complementary and additional tools to GRBs.