2005MNRAS.362L...4P

Long gamma-ray bursts (GRBs) are believed to be related to the explosion of Type Ic supernovae, which have been stripped of their hydrogen and helium envelopes. There appear to be two types of these explosions: those that are approximately spherical (GRB 980425/SN 1998bw), and which are associated with weak bursts; and the classical GRBs which generate ultrarelativistic jets (GRB 030329/SN 2003dh). If this bimodality is real, Swift will provide clear evidence for it.

We propose that classical powerful GRBs, which generate ultrarelativistic outflows, are a result of the formation of quark stars. Quark stars may provide additional energy for the explosion of Type Ic supernovae, but far more important is the creation of a surface which acts as a membrane that cannot be penetrated by baryons. A surface of a quark star allows only ultrarelativistic matter to escape: photons, neutrinos, electron-positron pairs and magnetic fields. The formation of a quark star follows several minutes after the initial core collapse. Possible evidence for this time delay is provided by BATSE precursors to GRBs, as analysed by Lazzati.