TITLE: GCN CIRCULAR NUMBER: 14605 SUBJECT: GRB 130427A, LBT optical spectrum DATE: 13/05/08 15:46:33 GMT FROM: Peter Garnavich at U of Notre Dame P. Garnavich (Notre Dame) reports: A spectrum of the GRB 130427A afterglow was obtained with the Large Binocular Telescope (LBT+MODS1 instrument) on 2013 May 7.15 (UT), 9.8 days after the burst. The spectrum covers 340 nm to 950 nm and is dominated by a power-law continuum. Narrow Balmer, [OII], [OIII] emission lines, and MgII and MgI absorption lines from the host galaxy are present at a redshift of 0.340. The LBT spectrum shows no obvious undulations characteristic of a broad-lined type Ic supernova such as SN 1998bw. In contrast, a 98bw-like supernova was detectable from GRB 030329 around seven days after its burst (Stanek et al. 2003, ApJ, 591, L17). This early detection was primarily due to the prominent peak seen around 500 nm (rest frame) in broad-lined type Ic events. Adding a pre-maximum spectrum of SN 1998bw (Patat et al. 2001, ApJ, 555, 900) to a power-law continuum suggests that any 98bw-like supernova is at least an R-band magnitude fainter than the afterglow 10 days after the GRB 130427A burst. I thank Rick Pogge, Paul Martini and Scott Adams for help in obtaining the spectra. The LBT is an international collaboration among institutions in the United States, Italy and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University, and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota and University of Virginia.