[IAUC] CBET 2392: 20100726 : SUPERNOVA 2007va

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                                                  Electronic Telegram No. 2392
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
CBAT Director:  Daniel W. E. Green; Room 209; Dept. of Earth and Planetary
 Sciences; Harvard University; 20 Oxford St.; Cambridge, MA  02138; U.S.A.
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SUPERNOVA 2007va
     S. Kozlowski and C. S. Kochanek, Department of Astronomy, Ohio State
University; D. Stern, Jet Propulsion Laboratory, California Institute of
Technology; J. L. Prieto, Carnegie Observatories, Pasadena; and K. Z. Stanek,
Department of Astronomy, Ohio State University, report the discovery of a
six-month-long mid-infrared transient in the Spitzer Deep Wide-Field Survey
(SDWFS; Ashby et al. 2009, Ap.J. 701, 428) data.  The transient was found in
the variability study of the SDWFS data (Kozlowski et al. 2010, Ap.J. 716,
530) as the most variable object with highly correlated light curves in 3.6-
and 4.5-micron Spitzer/IRAC bands.  Its position is R.A. = 14h26m23s.24, Decl.
= +35o35'29".1 (equinox 2000.0).
     The transient peaked on 2007 August 8-13 and was clearly detected in all
four Spitzer/IRAC bands from the second epoch of SDWFS.  It is also detected
in all four bands six months later (2008 February 2-6), and in 3.6-, 4.5-, and
5.8-micron bands on 2008 March 6-10.  Infrared magnitudes for the transient:
2004 Jan. 10-14, [3.6 microns] > 19.67, [4.5 microns] > 18.73, [5.8 microns] >
16.33, [8.0 microns] > 15.67 (not detected in 4" apertures at a 3-sigma level);
2007 Aug. 8-13, [3.6 microns] = 15.93, [4.5 microns] = 15.61; 2008 Feb. 2-6,
[3.6 microns] = 16.09, [4.5 microns] = 15.76; 2008 Mar. 6-10, [3.6 microns] =
17.99, [4.5 microns] = 17.72.
     On 2010 March 12, a Keck/LRIS spectrum was taken of the host galaxy to
learn that it is a low-luminosity (magnitude R approximately 22.8; estimated
absolute magnitude at 4.5 microns approximately -18.6), metal-poor, irregular
galaxy with z = 0.19.  The transient peaked at a mid-infrared absolute
magnitude of -24.2 (measured in a 4-arcsec aperture) in the 4.5-micron
Spitzer/IRAC band.  The transient at its peak was about 5 magnitudes brighter
in the mid-infrared than is the entire host galaxy.
     The Spitzer data are consistent with emission by a black body with a
temperature of about 1350 K and a total energy of at least 10^51 ergs.  The
most plausible scenario for the transient is a hyper-luminous type-IIn
supernova exploding inside a massive, optically thick circumstellar medium.
A number of non-supernova scenarios for explaining the transient were ruled
out, including:  an active galactic nucleus, gamma-ray burst, a Galactic star,
gravitational lensing, and a star disrupted by a black hole.
     Details on this object are presented in Kozlowski et al. (2010, Ap.J.,
submitted; see website URL http://lanl.arxiv.org/abs/1006.4162).


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                         (C) Copyright 2010 CBAT
2010 July 26                     (CBET 2392)              Daniel W. E. Green