TITLE: GCN CIRCULAR NUMBER: 16454 SUBJECT: GRB140606B/iPTF14bfu: Keck detection of an associated supernova DATE: 14/06/25 05:24:36 GMT FROM: Daniel Perley at Caltech D. A. Perley (Caltech), M. L. Graham, A. V. Filippenko (UC Berkeley), and S. B. Cenko (GSFC) report: We acquired a single 1200-second spectrum of iPTF14bfu (Singer et al., GCN 16360; Perley et al., GCN 16365), the optical transient associated with GRB 140606B (Burns et al., GCN 16363), using the Low Resolution Imaging Spectrometer (LRIS) on the Keck I 10-meter telescope. The observation was conducted starting at 13:00 UT on 2014-06-24, 18.4 days after the GBM trigger, and covers a wavelength range from 320-1028 nanometers. The spectrum shows several broad emission features and a significant decrease in flux toward both the blue and red ends. A comparison with SN 1998bw* using superfit (Howell et al. 2005, ApJ 634, 1190) shows a good match between the observed features and the spectrum of SN 1998bw near maximum light, indicating that the transient has evolved into a Type Ic-BL supernova. * http://www.astro.caltech.edu/~dperley/grb/140606b/140606b_98bw.png