2011CBET.2706....1S

M. Sparre, J. Fynbo, A. de Ugarte Postigo, and D. Malesani, Dark Cosmology Centre; and J. Sollerman, Oskar Klein Centre, on behalf of the X-shooter GTO GRB collaboration, report that medium-dispersion spectra (range 300-2200 nm, resolution 0.1 nm) of the afterglow associated with GRB 101219B (cf. GCN 11473, accessible at URL http://gcn.gsfc.nasa.gov/gcn3/11473.gcn3; position given as R.A. = 0:48:55.35, Decl. = -34:33:59.5, equinox 2000.0) were obtained with the Very Large Telescope (+ X-shooter) at the European Southern Observatory, Paranal, on three dates (at mean times 2010 Dec. 20.17, 2011 Jan. 5.09, and Jan. 25.55 UT, corresponding to 11.6 hr, 16.4 days, and 36.9 days after the burst, respectively). The exposure times were 80, 120, and 120 min, respectively. The first-epoch spectrum, where the afterglow is detected over the full spectral range, displays a power-law continuum typical for GRB afterglows (cf. GCN 11579). The fully reduced second-epoch spectrum, however, is best matched with a fading afterglow dominating the bluest regions, whereas the 500- to 900-nm region is well matched with the spectrum of the broad-lined type-Ic supernova 1998bw (Patat et al. 2001, Ap.J. 555, 900) taken eight days after outburst. The third-epoch spectrum contains less signal but is still fully consistent with a supernova spectrum, given the redshift of z = 0.55 (GCN 11579). The designation 2010ma is assigned to this supernova.