GRB 090618: a candidate for a neutron star gravitational collapse onto a black hole induced by a type Ib/c supernova

Dipartimento di Fisica and ICRASapienza Università di Roma, P.le Aldo Moro 5, 00185 Rome, Italy ICRANet, P.zza della Repubblica 10, 65122 Pescara, Italy
e-mail: luca.izzo@icra.it; jorge.rueda@icra.it; ruffini@icra.it

Received: 13 June 2012
Accepted: 16 October 2012

Abstract

A novel concept has recently been 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) onto a black hole (BH), induced by a type Ib/c SN explosion. We applied these considerations to the exceptional case of GRB 090618, for which there is evidence of an SN ~ 10 days after the GRB occurrence. We calculated the accretion rate and total accreted mass onto an NS from an SN Ib/c that originated from a companion evolved star. These calculations show that the NS reaches the critical mass in a few seconds and undergoes gravitational collapse onto a BH, leading to the emission of a GRB. We find for the mass of the NS companion, M_NS, and for the SN core progenitor, M_core, the following mass ranges: 1.8 ≲ M_NS/M_⊙ ≲ 2.1 and 3 ≤ M_core/M_⊙ ≤ 8. Finally, we discuss the complementarity of these considerations to alternative processes explaining long and short GRBs.