[IAUC] CBET 2799: 20110831 : SUPERNOVA 2011fh IN NGC 4806

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                                                  Electronic Telegram No. 2799
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 2011fh IN NGC 4806
     L. A. G. Monard, Calitzdorp, Western Cape, South Africa, reports his
discovery of an apparent supernova (mag 14.5) on unfiltered CCD images taken
on Aug. 24.746 and 25.716 UT at the Klein Karoo Observatory.  The new object
is located at R.A. = 12h56m14s.01, Decl. = -29d29'54".8 (equinox 2000.0),
which is 14" east and 21" north of the core of the galaxy NGC 4806; this
position coincides closely with a dense region of the galaxy that has a
starlike appearance (as seen on a red Digitized Sky Survey image).  Photometric
measurements on archived images taken at the Klein Karoo Observatory on
several occasions in 2011 showed a brightening of this region starting around
2011 Feb. 11.190 (mag 17.0) and gradually brightening to mag 16.4 around June
2.812 and to mag 16.0 on Aug. 2.710 (which was the last observation prior to
the discovery on Aug. 24).

     J. L. Prieto, Carnegie Observatories, reports than an optical spectrum
(range 370-930 nm; resolution 0.7 nm) of 2011fh was obtained on Aug. 29.0 with
the du Pont 2.5-m telescope (+ WFCCD) at Las Campanas Observatory.  The
spectrum has a blue continuum and strong emission lines from the Balmer series
that show multiple velocity components, which are characteristic of type-IIn
supernovae.  The H-alpha profile can be well-fitted with three Gaussian
components, including a narrow unresolved component and two relatively broad
resolved components with FWHM = 1600 and 7400 km/s.  Analysis of archival
pre-explosion Spitzer/IRAC 3.6- and 4.5-micron images of the host galaxy (NGC
4806), obtained in 2009 Aug. and Sept. (Program ID 60007, PI K. Seth) show a
mid-infrared point source at the position of 2011fh with flux densities 0.12
mJy (mag 15.9) at 3.6 microns and 0.11 mJy (mag 15.5) at 4.5 microns.  At the
distance of NGC 4806 (via NED; 33 Mpc from Virgo-infall corrected velocity),
these values imply luminosity densities of 3.5 x 10**6 and 2.5 x 10**6 solar
luminosity at 3.6 and 4.5 microns, respectively.  If this is a single source,
it would imply a very massive progenitor star.  However, note that the
spatial resolution of the Spitzer/IRAC images is approximately 260 pc (FWHM)
at the distance of NGC 4806, and this source could be an H II region.


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                         (C) Copyright 2011 CBAT
2011 August 31                   (CBET 2799)              Daniel W. E. Green