Constraints on Association of Single‐Pulse Gamma‐Ray Bursts and Supernovae

Abstract

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 ~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 ~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 σ 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.