HETE Observations of the Gamma-Ray Burst GRB 030329: Evidence for an Underlying Soft X-Ray Component

An exceptionally intense gamma-ray burst, GRB 030329, was detected and localized by the instruments on board the High Energy Transient Explorer satellite (HETE) at 11:37:14 UT on 2003 March 29. The burst consisted of two ~10 s pulses of roughly equal brightness and an X-ray tail lasting more than 100 s. The energy fluence in the 30-400 keV energy band was Sγ = 1.2 × 10-4 ergs cm-2, making GRB 030329 one of the brightest GRBs ever detected. Communication of a 2' error box 73 minutes after the burst allowed the rapid detection of a counterpart in the optical, X-ray, and radio and the ensuing discovery of a supernova with most unusual characteristics. Analyses of the burst light curves reveal the presence of a distinct, bright, soft X-ray component underlying the main GRB; the 2-10 keV fluence of this component is ~7 × 10-6 ergs cm-2. The main pulses of GRB 030329 were preceded by two soft, faint, nonthermal bumps. We present details of the HETE observations of GRB 030329.