Classification of CSS100317:123527+270403

ATel #2501; A. V. Filippenko, J. M. Silverman, I. K. W. Kleiser, and A. J. L. Morton (University of California, Berkeley)
on 23 Mar 2010; 02:25 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Alexei V. Filippenko (alex@astro.berkeley.edu)

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We report that inspection of CCD spectra (range 340-1000 nm), obtained on March 22 UT with the 3-m Shane reflector (+ Kast) at Lick Observatory, shows that CSS100317:123527+270403 (ATel #2490) is a broad-lined Type Ic supernova similar to SN 1998bw (e.g., Patat et al. 2001, ApJ, 555, 900), probably within a few days of maximum brightness. The redshift of the host galaxy, determined from strong, narrow emission lines produced by H II regions in the host galaxy, is 0.067, in agreement with ATel #2490. By far the most prominent feature is a very broad peak centered roughly at rest wavelength 515 nm. Given that such supernovae are sometimes associated with long-duration gamma-ray bursts (e.g., Woosley & Bloom 2006, ARAA, 44, 507), a search for a possibly corresponding GRB in the weeks prior to discovery (March 17) should be conducted. Further observations of the supernova are encouraged.