GRB 090618: The First Example of a Neutron Star Gravitational Collapse to a Black Hole Induced by a Type Ib/c Supernova

Abstract

A novel concept has been recently proposed for explaining the temporal coincidence of some Gamma Ray Bursts (GRBs) with an associated Supernova (SN) in terms of the gravitational collapse of a neutron star (NS) to a Black Hole (BH), induced by a type Ib/c SN explosion. We apply these considerations to the exceptional case of GRB 090618, for which there is evidence of a SN $\sim 10$ days after the GRB occurrence. We calculate the accretion rate and total accreted mass onto a NS from a SN Ib/c originated from a companion evolved star. It is shown that the NS reaches in a few seconds the critical mass and undergoes gravitational collapse to a BH leading to the emission of a GRB. We find for the mass of the NS companion, $M_{\rm NS}$, and for the SN core progenitor, $M_{\rm core}$, the following mass ranges: $1.8\lesssim M_{NS}/M_\odot \lesssim 2.1$ and $3\leq M_{\rm core}/M_\odot \leq 8$. Finally, we discuss the complementarity of these considerations to alternative processes explaining long and short GRBs.