A search for $\mathit{\text{Fermi}}$ bursts associated to supernovae and their frequency of occurrence

Context: Observations suggest that the major fraction of long duration gamma-ray bursts (GRBs) are connected with broad-lines supernovae Ib/c, (SNe-Ibc). The presence of GRB-SNe is revealed by rebrightenings emerging from the optical GRB afterglow $10$–$15$ days, in the rest-frame of the source, after the prompt GRB emission. Aims: $\mathit{\text{Fermi}}$-GBM has a field of view (FoV) which is about 6.5 times larger than the FoV of $\mathit{\text{Swift}}$, therefore we expect that a number of GRB-SN connections have been missed due to lack of optical and X-ray instruments on board of $\mathit{\text{Fermi}}$, which are essential to reveal SNe associated with GRBs. This fact has motivated our search in the $\mathit{\text{Fermi}}$ catalogue for possible GRB-SN events. Methods: The search for possible GRB-SN associations follows two requirements: (1) SN should fall inside the $\mathit{\text{Fermi}}$-GBM error box of the considered long GRB, and (2) this GRB should occur within $20$ days before the SN event. Results: We have found $5$ cases, within $z<0.2$ fulfilling the above reported requirements. One of them, GRB 130702A-SN 2013dx, was already known as GRB-SN association. We have analyzed the remaining $4$ cases and we concluded that three of them are, very likely, just random coincidences, due to the $\mathit{\text{Fermi}}$-GBM large error box associated with each GRB detection. We found one GRB possibly associated with a SN 1998bw-like, GRB 120121B/SN 2012ba. Conclusions: The very low redshift of GRB 120121B/SN 2012ba ($z=0.017$) implies a low isotropic energy of this burst ($E_{iso}=1.39\times {10}^{48}$) erg. We then compute the rate of $\mathit{\text{Fermi}}$ low-luminosity GRBs connected with SNe to be $\rho_{0,b} \leq 770\ $Gpc$^{-3}$yr$^{-1}$. We estimate that $\mathit{\text{Fermi}}$-GBM could detect $1$–$4$ GRBs-SNe within $z\le 0.2$ in the next 4 years.