A new type of long gamma-ray burst

We consider gamma–ray bursts produced by the merger of a massive white dwarf with a neutron star. We show that these are likely to produce long–duration GRBs, in some cases definitely without an accompanying supernova, as observed recently. This class of burst would have a strong correlation with star formation, and occur close to the host galaxy. However rare members of the class need not be near star–forming regions, and could have any type of host galaxy. Thus a long–duration burst far from any star–forming region would also be a signature of this class. Estimates based on the existence of a known progenitor suggest that our proposed class may be an important contributor to the observed GRB rate.