Electronic Telegram No. 1427
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT@CFA.HARVARD.EDU (science)
URL http://www.cfa.harvard.edu/iau/cbat.html


SUPERNOVA 2008dx
     D. Chamarro, A. Uecker, F. Yuan, M. D. Sisson, C. Akerlof, and T. Mckay,
University of Michigan; R. Quimby, California Institute of Technology; and
J. C. Wheeler, University of Texas, on behalf of the ROTSE collaboration,
report the discovery of an apparent supernova (mag about 17.4) in unfiltered
CCD images taken on June 24.20 and 24.23 UT with the 0.45-m ROTSE-IIIb
telescope at McDonald Observatory.  SN 2008dx is located at R.A. =
13h00m14s.31, Decl. = +27o57'16".4 (equinox 2000.0; uncertainty < 1"), which
is about 339" east and 94" south from the center of the Coma cluster and
44".6 west and 2".6 south from the center of the nearest galaxy seen in the
Sloan Digital Sky Survey (2MASX J13001768+2757192).  Nothing is visible at
this position on an image taken on June 23.2 (limiting mag about 18.1).  A
ROTSE-III finding chart can be found at the following website URL:
http://www.rotse.net/rsvp/j130014.3+275716/j130014.3+275716.jpg
     S. Blondin, Harvard-Smithsonian Center for Astrophysics (CfA), on
behalf of the CfA Supernova Group, reports that a spectrum (range 350-740
nm) of 2008dx, obtained on June 27.26 UT by M. Calkins with the F. L.
Whipple Observatory 1.5-m telescope (+ FAST), shows it to be a type-Ia
supernova around one week before maximum light.  Cross-correlation with a
library of supernova spectra using the "Supernova Identification" code
(Blondin and Tonry 2007, Ap.J. 666, 1024) indicates that 2008dx is most
similar to the subluminous type-Ia supernova 2000cn (Matheson et al. 2008,
A.J. 135, 1598) at nine days before maximum, at a redshift cz = 10500 +/-
1200 km/s.  Adopting this recession velocity for the supernova, the maximum
absorption in the Si II line (rest 635.5 nm) is blueshifted by roughly
13500 km/s.  Assuming that the galaxy is in the Hubble flow and the
supernova suffers negligible extinction, the discovery magnitude of 17.4
corresponds to an absolute magnitude of roughly -18.5, which is brighter
than that of SN 1991bg and comparable to normal type-Ia supernovae at
the same age.


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2008 CBAT
2008 July 3                      (CBET 1427)              Daniel W. E. Green