A search for Fermi bursts associated with supernovae and their frequency of occurrence

Abstract

Context. Observations suggest that most long duration gamma-ray bursts (GRBs) are connected with broad-line supernovae Ib/c, (SNe-Ibc). The presence of GRB-SNe is revealed by rebrightenings emerging from the optical GRB afterglow days, in the rest-frame of the source, after the prompt GRB emission. Aims. Fermi/GBM has a field of view (FoV) about 6.5 times larger than the FoV of Swift, therefore we expect that a number of GRB-SN connections have been missed because of lack of optical and X-ray instruments on board of Fermi, which are essential for revealing SNe associated with GRBs. This has motivated our search in the Fermi catalog for possible GRB-SN events. Methods. The search for possible GRB-SN associations follows two requirements: (1) SNe should fall inside the Fermi/GBM error box of the considered long GRB, and (2) this GRB should occur within days before the SN event. Results. We have found five cases within fulfilling the above reported requirements. One of them, GRB-130702A-SN 2013dx, was already known to have a GRB-SN association. We have analyzed the remaining four cases and we have concluded that three of them are, very likely, just random coincidences due to the Fermi/GBM large error box associated with each GRB detection. We found one GRB possibly associated with a SN 1998bw-like source, GRB 120121B/SN 2012ba. Conclusions. The very low redshift of GRB 120121B/SN 2012ba implies a low isotropic energy of this burst erg. We then compute the rate of Fermi low-luminosity GRBs connected with SNe to be Gpc. We estimate that Fermi/GBM could detect GRBs-SNe within in the next 4 years.