Spectroscopic Discovery of the Supernova 2003dh Associated with GRB 030329

TLDR

The study reports early afterglow observations of GRB 030329 and the spectroscopic detection of its associated supernova SN 2003dh. Spectra were collected nightly from 0.6 to 9.6 days after the burst, spanning 350–850 nm. The spectra reveal a low‑redshift (z = 0.1687) afterglow with a power‑law continuum, and after April 5 show broad supernova features matching SN 1998bw, providing the first direct spectroscopic confirmation that some classical GRBs arise from supernovae.

Abstract

We present early observations of the afterglow of GRB 030329 and the spectroscopic discovery of its associated supernova SN 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 350-850 nm. The early spectra consist of a power-law continuum (Fν ∝ ν-0.9) with narrow emission lines originating from H II regions in the host galaxy, indicating a low redshift of z = 0.1687. However, our spectra taken after 2003 April 5 show broad peaks in flux characteristic of a supernova. Correcting for the afterglow emission, we find that the spectrum of the supernova is remarkably similar to the Type Ic "hypernova" SN 1998bw. While the presence of supernovae has been inferred from the light curves and colors of gamma-ray burst afterglows in the past, this is the first direct, spectroscopic confirmation that a subset of classical gamma-ray bursts originate from supernovae.