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T. Matheson (CfA), P.M. Garnavich (Notre Dame), K.Z. Stanek (CfA), P.A. Mazzali (RESCEU, Tokyo, INAF), J. Deng (RESCEU, Tokyo), N. Tominaga, K. Maeda (Tokyo), K. Nomoto (RESCUE, Tokyo), K.S. Kawabata (NAOJ), D. Bersier (STScI), S.T. Holland (GSFC)
We present a series of optical spectra of supernova (SN) 2003dh and the afterglow of its associated gamma-ray burst (GRB) 030329. Using early observations of the GRB afterglow, we separate the GRB and SN components in later spectra, revealing the nature of the SN itself. The SN first appears ~7 days after the burst, and dominates the light after ~11 days. We show, taking into account cosmological time dilation, that the spectroscopic evolution of SN 2003dh follows closely that of SN 1998bw, a peculiar Type Ic SN associated with GRB 980425. The supernova explosion occurs close to the time of the GRB. At later times, SN 2003dh resembles SN 1997ef, another highly energetic, peculiar Type Ic SN. Modeling the spectra and light curve shows that SN 2003dh was also very energetic and shares some properties with both SNe 1998bw and 1997ef. There are strong indications that the explosion was asymmetric.
We would like to thank the staffs of the MMT, FLWO, Las Campanas, Lick, Keck, Subaru, and Kitt Peak National Observatories.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.