{
  "bibcode": "2008GCN..7169....1M",
  "body": "D. Malesani, J. Hjorth (DARK), P. Jakobsson (Univ. Hertfordshire), P.M. \nVreeswijk, C.C. Thoene, J.P.U. Fynbo, D.J.  Watson, J. Sollerman (DARK), \nN.R. Tanvir (Univ. Leicester), T. Stanke (ESO), report on behalf of a \nlarger collaboration:\n\nWe observed the optical transient in NGC 2770 (Berger & Soderberg, GCN \n7159; Deng & Zhu, GCN 7160), denoted SN 2008D (Li & Filippenko, IAUC \n1202), with the ESO VLT equipped with FORS2, starting on 2008 Jan 11, \n07:17 UT. Two spectra, at low and moderate resolution, were acquired, \ncovering the wavelength ranges ~3700-6350 and ~3800-9000 AA. The \nexposure times were 10 and 15 minutes, respectively. The two spectra, \nafter flux calibration, agree very well in the overlap region, and the \npeak S/N is ~60 and ~40, respectively.\n\nWe detect a strong, red continuum revealing several broad features and \nbumps. The afterglow spectrum does not display a power-law shape. We \nalso detect Na I D in absorption at z = 0.0069. This redshift is very \nsimilar to that of the host z=0.0071, as measured for the Halpha and \nHbeta lines in emission superimposed on the transient. The detection of \nNa I D confirms that the object is of extragalactic origin. It also \nimplies that it is subject to significant extinction. Although \nuncertain, using the relation by Munari & Zwitter (1997, A&A, 318, 269), \nwe estimate E(B-V) to be larger that ~0.5 mag based on the equivalent \nwidth of the 5890 A line EW = 0.67 AA. Such relatively large extinction \nis consistent with the detection of excess column density in the X-ray \nspectra of the flare (Berger & Soderberg, GCN 7159).\n\nThe spectral shape of the transient rules out a significant nonthermal \nafterglow component. The presence of broad features is reminiscent of SN \nspectra, although it is not straightforward to identify the involved \ntransitions. The lack of prominent Silicon and Hydrogen lines suggests \nthe SN is not of type Ia or II. By exclusion, we suggest the transient \nis a SN of type Ib/c. The features are not as broad as in the earliest \nspectra of GRB-associated SNe such as SN1998bw and SN2006aj.\n\nThe luminosity of the event is also comparable to that of other \ncore-collapse SNe associated with GRBs. The object had V~19.3 \napproximately 1.5 days after the X-ray transient (Thoene et al., GCN \n7161). Taking into account the large extinction (> 1.5 mag in V), the \nluminosity is comparable with that of core-collapse SNe soon after the \nexplosion. As noted by several authors, the available light curve is \nalso consistent with a SN (Valenti et al., GCN 7163; Kong et al., GCN \n7164, Li & Filippenko, CBET 1202).\n\nIn conclusion, the bright absolute magnitude of the object, M_V < -14,  \nthe broad spectral features, and the lack of H and Si strongly suggest \nthat the transient in NGC 2770 is a SN of type Ib/c.\n\nLastly, we note that the transient does not seem to lie in an intense \nstar forming region of its host, as suggested by the modest nebular \nfeatures detected in our spectrum and the absence of prominent emission \nat the position of the optical transient (D'Elia et al., GCN 7162) in \nthe archival SDSS images. We caution that strong extinction may affect \nthis arguments.\n\nWe acknowledge excellent support of the observing staff at Paranal, in \nparticular Cedric Ledoux, Linda Schmidtobreick, and Antonio de Ugarte \nPostigo.\n\n[GCN OPS NOTE(13jan08): Per author's request, the \"IAUC 1202\" citation\nwas changed to \"CBET 1202\" (at the end of the 4th paragraph).]",
  "circularId": 7169,
  "createdOn": 1200085274000,
  "email": "malesani@astro.ku.dk",
  "subject": "Transient in NGC 2770: spectroscopic evidence for a SN",
  "submitter": "Daniele Malesani at Niels Bohr Inst,Dark Cosmology Center  <malesani@astro.ku.dk>"
}