Spectroscopic Discovery of the Supernova 2003dh Associated with GRB 030329

We present early observations of the afterglow of the Gamma-Ray Burst (GRB) 030329 and the spectroscopic discovery of its associated supernova 2003dh. We obtained spectra of the afterglow of GRB 030329 each night from March 30. 12 (0. 6 days after the burst) to April 8. 13 (UT) (9. 6 days after the burst). The spectra cover a wavelength range of 350 nm to 850 nm. The early spectra consist of a power-law continuum (F₍ₔ ~ nu^-0. 9) with narrow emission lines originating from HII regions in the host galaxy, indicating a low redshift of z=0. 1687. However, our spectra taken after 2003 Apr. 5 show broad peaks in flux characteristic of a supernova. Correcting for the afterglow emission, we find the spectrum of the supernova is remarkably similar to the type Ic `hypernova' SN 1998bw. While the presence of supernovae have been inferred from the light curves and colors of GRB afterglows in the past, this is the first direct, spectroscopic confirmation that a subset of classical gamma-ray bursts originate from supernovae.