A new type of long gamma-ray burst

We consider gamma-ray bursts (GRBs) 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.