[IAUC] CBET 1204: 20080111 : SUPERNOVA 2008D IN NGC 2770

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                                                  Electronic Telegram No. 1204
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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SUPERNOVA 2008D IN NGC 2770
      S. Blondin, Harvard-Smithsonian Center for Astrophysics (CfA), on
behalf of the CfA Supernova Group; T. Matheson, National Optical Astronomy
Observatory; and M. Modjaz, University of California at Berkeley, report
that a spectrum (range 320-840 nm) of 2008D (cf. CBET 1202), obtained on
Jan. 11.41 UT by P. Berlind with the MMT 6.5-m telescope (+ Blue Channel
spectrograph), shows it most likely to be a peculiar type-Ic supernova in
its early phases.  The spectrum consists of a relatively blue continuum,
with P-Cyg profiles (FWHM of approximately 10000 km/s) that are
characteristic of a supernova spectrum blueward of 550 nm, and an extremely
broad emission feature peaking at approximately 630 nm that is similar to
the [O I] doublet (rest 630.0, 636.4 nm) seen in the spectra of broad-line
type-Ic supernovae around maximum light.  More specifically, the double-
absorption feature centered on 420 nm resembles that seen in the earliest
spectrum of the normal type-Ic supernova 1990aa (cf. IAUC 5087, 5111;
Matheson et al. 2001, A.J. 121, 1648), while the broad feature centered on
630 nm resembles the [O I] bump seen in spectra of the broad-line type-Ic
supernova 1998bw (associated with GRB 980425; cf. IAUC 6895, 6901; Patat
et al. 2001, Ap.J. 555, 900) around maximum light (roughly three weeks
after the gamma-ray-burst detection).
     Blondin et al. add that their spectrum is not consistent with the
description given by Soderberg et al. in GCN 1765, who report on a "smooth,
featureless continuum" with "some suggestion of a broad bump near 5500
Angstroms".  However, based on other spectra of familiar objects fully
reduced from the same night, Blondin et al. are confident that their flux
and wavelength calibrations are accurate.  The separation in time between
the MMT spectrum and the one described in GCN 1765 is only 0.1 day.
Blondin et al. clearly detect narrow emission lines at the supernova
position, consistent with the NED redshift of 1934 km/s for NGC 2770 (from
The Updated Zwicky Catalog, http://tdc-www.harvard.edu/uzc/).  Also,
interstellar Na I D absorption at that redshift is visible in the spectrum
with an equivalent width of 0.2 nm.  A comparison plot can be seen at URL
http://www.cfa.harvard.edu/supernova/spectra/sn2008D_comp.gif; note that,
in this plot, the spectrum of SN 1990aa had to be blueshifted by 5500 km/s
in order for prominent spectroscopic features to match up with those
present in SN 2008D, while that of SN 1998bw has been redshifted by 13000
km/s for the same reason.

     S. Valenti, Universita di Ferrara; D. Fugazza and E. Maiorano, Istituto
Nazionale di Astrofisica (INAF), Osservatorio Astronomico di Bologna; V.
D'Elia and L. A. Antonelli, INAF, Ossevatorio Astronomico di Roma; S. Covino,
INAF, Osservatorio Astronomico di Brera; A. Magazzu and N. Pinilla-Alonso,
INAF, Telescopio Nazionele Galileo (TNG); M. Della Valle, INAF, Osservatorio
Astrofisico di Arcetri; G. Chincarini, Universita' degli Studi di Milano
Bicocca; E. Pian and P. A. Mazzali, INAF, Osservatorio Astronomico di Trieste;
and A. Harutyunyan and S. Benetti, INAF, Osservatorio Astronomico di Padova,
report that preliminary reduction of a spectrogram of 2008D, taken with the
TNG (+ LRS; range 350-780 nm) on Jan. 11.1 UT, shows that the spectrum
resembles that of the energetic type-Ic supernova 2006aj (cf. IAUC 8674) at
three days after explosion (Pian et al. 2006, Nature 442, 1011).  The Si II
635.5-nm feature shows a higher expansion velocity than in the spectrum of
2006aj.  The bluer bumps seen in the 2006aj spectrum, centered at about 440
and 500 nm, are not yet well developed, also suggesting a higher expansion
velocity.


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                         (C) Copyright 2008 CBAT
2008 January 11                  (CBET 1204)              Daniel W. E. Green