TITLE: GCN CIRCULAR NUMBER: 1911 SUBJECT: GRB 030226: Steep Decline DATE: 03/03/01 13:39:35 GMT FROM: Shri Kulkarni at Caltech S. R. Kulkarni, D. W. Fox, E. Berger and A. M. Soderberg, California Institute of Technology, Pasadena, CA 91125, USA report "We have continued observations of the optical afterglow (Fox, Chen and Price GCN 1879) of GRB 030226 (Suzuki et al. GCN 1888) with the Echellette Spectrograph Imager (ESI) mounted at the Cassegrain focus of of the Keck-II telescope. Over the last 24 hours (from epoch day 2.3 to day 3.3) the R band flux has faded by 1.6 +/- 0.1 magnitudes. If interpreted as a power law decay the power law index, alpha, is about 4 (flux, f(t) proportional to t^-alpha). Such a steep decline is unprecedented. Even a density discontinuity does not produce such a steep decrease (see Panaitescu & Kumar ApJ 541, L51, 2000). Substructure (in the ejecta or circumburst medium) or copious radiative losses can potentially account for the steep decline. Separately, we note that GRB 030226 with it's early steepening (``jet break time'' of 0.5 day; see Greiner et al. GCN 1894 and Zeh et al. GCN 1898) joins GRB 980519 and GRB 980326. These latter GRBs are notable for being under-energetic when compared to the known GRB sample and may form an interestind sub-class of cosmlogical GRBs (see Bloom, Frail and Kulkarni, astro-ph/0302210). The diversity both in energetics and circumburst density demonstrate that bursts are those which deviate from the sample are likely to be very interesting. Extrapolations of based on mean values of the current sample of GRBs can thus be misleading and lead observers astray."