There are some serious difficulties with this interpretation of the data for GRB 980425/SN 1998bw: the supernova occurred outside the NFI error circle of a fading X-ray source (Pian et al. 1998a, 1998b, 1999; Piro et al. 1998). This source had a temporal decay consistent with a power-law index of (Pian et al. 1998b), which resembles the temporal behavior of X-ray afterglows seen in almost every other GRB followed up with the SAX NFI. It must therefore be viewed as a strong candidate to be the X-ray afterglow of GRB 980425.
Moreover, if the association between GRB 980425 and SN 1998bw were true, the luminosity of this burst would be erg s-1 and its energy would be erg. Each would therefore be five orders of magnitude less than that of other bursts, and the behavior of the X-ray and optical afterglow would be very different from those of the other BeppoSAX bursts, yet the burst itself is indistinguishable from other BeppoSAX and BATSE GRBs with respect to duration, time history, spectral shape, peak flux, and and fluence (Galama et al. 1998).
In view of these difficulties, the safest procedure is to regard the association as a hypothesis that is to be tested by searching for correlations between SNe and GRB in catalogs of SNe and GRBs, excluding SN 1998bw and GRB 980425. Wang & Wheeler (1998a; see also Wang & Wheeler 1998b) have correlated BATSE GRB with Type Ia and with Type Ib-Ic Sne. They found that the data was "consistent'' with the assumption of an association between GRB and Type Ib-Ic SNe.
In the present work we improve upon the Wang & Wheeler correlative study by introducing an analysis method based on Bayesian inference, and therefore using the likelihood function, that incorporates information about the BATSE position errors in a non-arbitrary way and that is free of the ambiguities of a posteriori statistics. The method also accounts for the fact that the BATSE temporal exposure is less than unity.
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