Author: Andrew Levan
Abstract: We present observations of gamma-ray bursts with durations of several thousand seconds, and demonstrate that these events are extragalactic transients. We provide redshift measurements for several events, including GRB 101225A (the Christmas day burst). The afterglows and host galaxies of these GRBs are apparently different to those typically seen in "normal" GRBs. We argue that this implies that these bursts belong to a hitherto unrecognized population of ultra-long GRBs, whose progenitors may be quite different to those now identified with classical long-GRBs.