Constraints on association of single-pulse gamma-ray bursts and supernovae

We explore the hypothesis, similar to one recently suggested by Bloom and colleagues, that some nearby supernovae are associated with smooth, single-pulse gamma-ray bursts, possibly having no emission above similar to 300 keV. We examine BATSE bursts with durations longer than 2 s, fitting those which can be visually characterized as single-pulse events with a lognormal pulse model. The fraction of events that can be reliably ascertained to be temporally and spectrally similar to the exemplar, GRB 980425-possibly associated with SN 1998bw-is 4/1573 or 0.25%. This fraction could be as high as 8/1573 (0.5%) if the dimmest bursts are included. Approximately 1.5% of bursts are morphologically similar to GRB 980425 but have emission above similar to 300 keV. A search of supernova catalogs containing 630 detections during BATSE's lifetime reveals only one burst (GRB 980425) within a 3 month time window and within the total 3 sigma BATSE error radius that could be associated with a Type Ib/c supernova. Thus, we find no further evidence to support a single-pulse GRB and SN Ib/c connection. We also find no tendency for any set of single-pulse GRBs to fall near the supergalactic plane, whereas SNe of Type Ib/c do show this tendency-evidence that the two phenomena are not related.