Gamma Ray Bursts from delayed quark-deconfinement phase transition in neutron stars

There have been recently strong observational indications [1] about the possibility that some Gamma-Ray Bursts (GRBs) can take place years after a supernova, (SN) explosion due to some mechanism involving the compact star left by the stellar collapse associated to the supernova. In the present work, we propose a model to explain this possible "delayed" GRB-SN association. Our model is based on the conversion of a pure hadronic star (neutron star) into a star made at least in part of deconfined quark matter. The conversion process can be delayed if the surface tension of the interface between the hadronic and deconfined quark matter phases is taken into account. The nucleation time (i.e. the time to form a critical-size drop of quark matter) can be extremely long if the mass of the star is small. Via mass accretion the nucleation time can be dramatically reduced and the star is finally converted from the metastable into the stable configuration. A huge amount of energy, of the order of 10(52)-10(53) erg, is released during the conversion process and can produce a powerful gamma ray burst. The delay between the supernova, explosion generating the metastable neutron star and the stellar conversion can explain the delay observed in GRB990705 [1] and in GRB011211 [2].