[IAUC] CBET 3111: 20120519 : SUPERNOVA 2012cg IN NGC 4424 = PSN J12271283+0925132

Sab Mayo 19 17:00:57 ART 2012

                                                  Electronic Telegram No. 3111
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 2012cg IN NGC 4424 = PSN J12271283+0925132
     Further to CBET 3105, M. Kandrashoff, S. B. Cenko, W. Li, and A. V.
Filippenko report the LOSS discovery of an apparent supernova on unfiltered
KAIT images:

 SN       2012 UT       R.A. (2000.0) Decl.      Mag.      Offset
 2012cg   May 17.22   12 27 12.83  + 9 25 13.2   16.9    17".3 E, 1".5 S

The variable was designated PSN J12271283+0925132 when it was posted at the
Central Bureau's TOCP webpage and is here designated SN 2012cg based on the
spectroscopic confirmation reported below.  Additional CCD magnitudes for
2012cg (unfiltered unless noted otherwise):  May 12.30 UT, [18.5 (KAIT);
14.87, [19.0 (G. Cortini, Predappio, Italy; Celestron C14 telescope +
Starlight X-Press SXVR H9 camera); 17.26, 16.8 (KAIT); 18.332, 14.9 (Joseph
Brimacombe, Cairns, Australia; luminance filter; position end figures 12s.84,
13".1; image posted at http://www.flickr.com/photos/43846774@N02/7225356298/);
18.840, R_c = 15.1 (Massimiliano Martignoni, Magnago, Italy; 0.25-m f/10
reflector; position end figures 12s.82, 12".9); 18.89, 15.2 (Cortini);
18.975, 14.9 (Federica Luppi and Luca Buzzi, Varese, Italy; 0.38-m f/6.8
reflector; position end figures 12s.84, 13".1; reference stars from CMC-14
catalogue; image posted at http://www.astrogeo.va.it/pub/TOCP/PSN_N4424.jpg).

     S. B. Cenko, A. V. Filippenko, and J. M. Silverman, University of
California, Berkeley; and A. Gal-Yam, Weizmann Institute of Science, report
that a CCD spectrum (range 340-800 nm) obtained on May 18 UT by L. Pei, M.
Nguyen, D. Carson, and A. J. Barth (University of California, Irvine) with
the Kast double spectrograph on the Shane 3-m telescope at Lick Observatory
shows that 2012cg is probably a very young type-Ia supernova.  The spectrum
resembles that of SN 1990N about two weeks before maximum brightness
(Leibundgut et al. 1991, Ap.J. 371, L23).  Intensive follow-up observations
at all wavelengths are encouraged.

     G. H. Marion, R. P. Kirshner, and R. J. Foley, Harvard-Smithsonian
Center for Astrophysics (CfA); and P. Challis, Australian National University,
on behalf of the CfA Supernova Group, report that a spectrum (range 340-740
nm) of PSN J12271283+0925132 = 2012cg was obtained on May 18 UT by J. Irwin
with the F. L. Whipple Observatory 1.5-m telescope (+ FAST).  Cross-
correlation with a library of supernova spectra using the "Supernova
Identification" code (SNID; Blondin and Tonry 2007, Ap.J. 666, 1024) shows
that the object is a very early type-Ia supernova.  A fit is found to the
template of SN 1990N at -13 days.  Na I D and Ca II H and K interstellar
lines are quite strong in the spectrum from 2012cg but the region near 420.0
nm is much shallower than the deep absorption at this wavelength in the
template spectrum from SN 1990N at -13 days.  The Si II 635.5-nm absorption
feature of 2012cg has two components at approximately 21000 and 11000 km/s
with the high-velocity component being stronger.  Using a redshift of z =
0.001458 for NGC 4424 (Kent et al. 2008, A.J. 136, 713).

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

                         (C) Copyright 2012 CBAT
2012 May 19                      (CBET 3111)              Daniel W. E. Green