[vsnet-grb-info 5549] Transient 080109/SN 2008D: Spectroscopic Evolution and Re-Classification

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7212
SUBJECT: Transient 080109/SN 2008D: Spectroscopic Evolution and Re-Classification
DATE:    08/01/24 01:08:45 GMT
FROM:    Maryam Modjaz at UC Berkeley  <mmodjaz at astro.berkeley.edu>

M. Modjaz, R. Chornock, R. J. Foley, A. V. Filippenko, and W. Li (UC
Berkeley); and G. Stringfellow (U of Colorado) report on behalf of a
larger collaboration:

"We obtained optical spectra of SN 2008D (Li & Filippenko, CBET 1202;
Soderberg et al., GCN 7165; Malesani et al., GCN 7169; Valenti et al.,
GCN 7171; Blondin et al., CBET 1205, see also GCN 7160-7168). 
A spectrum (range 350-970 nm) taken on Jan 21.22 UT with the ARC
3.5-m telescope (+ DIS) at APO shows it to be a type-Ib supernova.
The fully reduced spectrum shows the development of conspicuous lines
of He I (rest 447.1, 587.6, 667.8, 706.5 nm) with the maximum absorptions
blueshifted by roughly 10,000-11,000 km/s (assuming a recession velocity
for the host galaxy of 1947 km/s). 

This spectrum, when de-reddened by A_V ~ 2 mag, is very similar to
spectra of SN Ib 2005hg (CBET 271; Modjaz et al., in prep), about 1
week before maximum. Cross-correlation with a library of supernova
spectra using the "Supernova Identification" code (SNID; Blondin and
Tonry 2007, Ap.J. 666, 1024) indicates that the spectrum of SN 2008D
is also similar to that of SN Ib 1998dt (Matheson et al. 2001,
A.J. 121, 1648) at maximum light. We furthermore detect strong
absorption at 615 nm which could be due to Si II (rest 635.5 nm) at
10,000 km/s or alternatively, very high-velocity H-alpha at 19,000
km/s. SN 2008D is the SN associated with the X-Ray Transient 080109
(Berger & Soderberg, GCN 7159; Kong & Marcone, ATEL 1355) and was
previously classified as peculiar type-Ic supernova (Blondin et al.,
Valenti et al. CBET 1205) based on very early spectra, and later as a
normal type-Ic SN (Malesani et al. GCN 7184) with possibly some He as
seen in NIR spectra (Marion et al. GCN 7188)."