GCN Circular 2107
T. Matheson (CfA), P. Garnavich (Notre Dame), N. Hathi, R. Jansen, R. Windhorst, L. Echevarria (ASU), J. Lee (Arizona), W. Brown, N. Caldwell, P. Berlind. M. Calkins and K. Z. Stanek (CfA) report: We obtained spectra of the afterglow of GRB 030329 (Peterson & Price, GCN 1985; Torii: GCN 1986) with the 6.5-m MMT and Blue-Channel spectrograph each night from March 30.12 to April 6.15 (UT). The spectra cover a wavelength range of 350 nm to 850 nm with a resolution of 0.6 nm (FWHM). The early spectra consist of a power-law continuum with narrow emission lines originating from HII regions in the host galaxy (Martini et al. GCN 2013; Della Ceca et al. GCN 2015; Greiner et al. GCN 2020; Caldwell et al. GCN 2053). However, our spectrum taken Apr. 6.15 (UT) shows a broad peak in flux at approximately 570 nm and another weak deviation from a power-law near 470nm that were not evident in the earlier spectra. The April 6 spectrum is well reproduced by adding a spectrum of SN 1998bw (Patat et al. 2001, ApJ, 555, 900) seven days before maximum light to a power-law distribution. We conclude that a supernova spectrum is emerging from the afterglow light. The brightness of the supernova is approximately V=22 based on the strengths of the broad features relative to a pure power-law. Further spectroscopy is planned. A plot of the spectrum compared with SN 1998bw is available at: http://cfa-www.harvard.edu/~tmatheson/grb030329_sn.jpg This message may be cited.