5 GRB 980425 (=SN 1998bw?)

During the past year, there has been considerable discussion regarding the association of GRB 980425 with the unusual supernova SN 1998bw. If the physical association is real it would provide an example of a very under-luminous (or mis-aligned, if strong beaming is assumed) gamma-ray burst, as well as a better understanding of the relationship of these two explosive phenomena. In the BATSE data, GRB 980425 does not appear to be unusual in any sense. The observed peak photon flux, 1.25 ph cm^-2 s^-1 (50 to 300 keV), is $\sim\!30\times$ less than the largest peak flux seen with BATSE from a GRB. The burst duration, as measured by the BATSE T₉₀ characterization (Kouveliotou et al. 1993a), is 23 s. The morphology of this burst is a single smooth peak; this shape has been compared to many others observed with BATSE (Bonnell et al. 1999). GRB 980425 has a soft spectrum, with very little emission above 300 keV and an $E_{\rm p} \sim$ 200 keV. This type of spectrum is observed in $\sim$20% of GRBs.