[IAUC] CBET 2711: 20110504 : SUPERNOVA 2011cb IN PGC 69707 = PSN J22470700-6449430

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                                                  Electronic Telegram No. 2711
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
CBAT Director:  Daniel W. E. Green; Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
e-mail:  cbatiau en eps.harvard.edu (alternate cbat en iau.org)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network


SUPERNOVA 2011cb IN PGC 69707 = PSN J22470700-6449430
     Greg Bock, Windaroo, Queensland, Australia, reports the discovery by
Stuart Parker (Oxford, Canterbury, New Zealand) of an apparent supernova
(mag 14.9) on an unfiltered CCD image obtained on Apr. 29.68 UT with a
35-cm Celestron C14 f/6.3 reflector (+ ST10 CCD camera) in the course of
the Backyard Observatory Supernova Search.  The new object (which was
designated PSN J22470700-6449430 when posted at the Central Bureau's TOCP
webpage and is here designated SN 2011cb based on the spectroscopic report
below) was reported by Stuart to be located at R.A. = 22h47m07s.00, Decl. =
-64d49'43".0 (equinox 2000.0).  Bock measured 2011cb to be at position end
figures 07s.49, 43".4, which is 8" east and 7" north of the nucleus of the
galaxy PGC 69707.  Nothing is visible at this position on red and infrared
images from the Digitized Sky Survey (limiting mag > 19).  Additional
magnitudes for 2011cb:  Apr. 30.508, 15.1 (Stuart; measured by Bock); 30.808,
15.2 (Joseph Brimacombe, Cairns, Australia, 30-cm reflector + STL6K camera +
red filter; position end figures 06s.9, 43".3); May 1.800, 15.2 (Brimacombe).
Brimacombe's Apr. 30 image is posted at the following website URL:
http://www.flickr.com/photos/43846774@N02/5676226310/; his May 1 image is
posted at http://www.flickr.com/photos/43846774@N02/5679218216/.

     M. Stritzinger, Oskar Klein Centre, Stockholm University; N. Morrell,
Las Campanas Observatory; and G. Folatelli, IPMU, University of Tokyo, report
on spectra (range 360-1011 nm) of SN 2011cb taken on May 1.3 and 2.3 UT by B.
Madore of the Carnegie Observatories.  Both spectra were obtained at Las
Campanas Observatory with the 2.5-m du Pont telescope (+ WFCCD), and they show
that 2011cb is a type-IIb supernova.  Comparison with a library of supernova
spectra via the Supernova Identification tool (SNID; Blondin and Tonry, 2007,
Ap.J. 666, 1024) shows that 2011cb is very similar to SN 1997dd as observed
on 1997 Sept. 6 and that it also resembles other type-IIb events around
maximum light.  The spectra exhibit prevalent P-Cyg absorption lines
associated with the the Balmer series and Ca II.  Additional features related
with He I are visible, most noticeably He I 587.6-nm, which is probably
blended with Na I D.  Features related to the Fe II multiplet 42 are also
discernible.  Adopting a host-galaxy recession velocity of 2366 km/s for PGC
69707 (Koribalski et al. 2004, A.J. 128, 16), expansion velocities of 13000
km/s and 12500 km/s for the first and second epochs, respectively, are
obtained from the absorption minimum of H-alpha.


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

                         (C) Copyright 2011 CBAT
2011 May 4                       (CBET 2711)              Daniel W. E. Green