Abstract

Observations of gamma-ray burst (GRB) afterglows have yielded tantalizing hints that supernovae (SNe) and GRBs are related. The case had been circumstantial, though, relying on irregularities in the light curve or the colors of the afterglow. I will present observations of the optical afterglow of GRB 030329. The early spectra show a power-law continuum, consistent with other GRB afterglows. After approximately one week, broad peaks in the spectrum developed that were remarkably similar to those seen in the spectra of the peculiar Type Ic SN 1998bw. This is the first direct, spectroscopic confirmation that at least some GRBs arise from SNe.

Introduction

The mechanism that produces gamma-ray bursts (GRBs) has been the subject of considerable speculation during the four decades since their discovery (see Mészáros 2002 for a recent review of the theories of GRBs). Optical afterglows (e.g., GRB 970228: Groot et al. 1997; van Paradijs et al. 1997) opened a new window on the field (see, e.g., van Paradijs, Kouveliotou, & Wijers 2000). Subsequent studies of other bursts yielded the redshifts of several GRBs (e.g., GRB 970508: Metzger et al. 1997), providing definitive evidence for their cosmological origin.

Models that invoked supernovae (SNe) to explain GRBs were proposed from the very beginning (e.g., Colgate 1968; Woosley 1993; Woosley & MacFadyen 1999). A strong hint was provided by GRB 980425. In this case, no traditional GRB optical afterglow was seen, but a supernova, SN 1998bw, was found in the error box of the GRB (Galama et al. 1998a).