2001ApJ...546L..29S

In this Letter, I put forward a model in which GRB 980425 is both associated with SN 1998bw and also a standard canonical (long; approximately a few seconds) gamma-ray burst (GRB). Herein it is argued that if GRBs are relativistic jets with the fastest moving material at the core, then the range of observed jet inclinations to the line of sight produces a range in the observed properties of GRBs, i.e., the lag-luminosity relationship. In particular, if the jet inclination is high enough, the observed emitter will move slowly enough to render relativistic beaming ineffective, thus distinguishing the jet from apparent isotropic emission. Thus, we expect a break in the lag-luminosity relationship. I propose that GRB 980425 defines that break. The position of this break gives important physical parameters such as the Lorentz factor (γ_max∼1000), the jet opening angle (∼1°), and thus the beaming fraction (∼10^–4). Estimates of burst rates are consistent with observation. If correct, this model is evidence in favor of the collapsar mode as the progenitor of cosmological, long GRBs.