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THE ASTRONOMER Electronic Circular No 2460      2008 Jly 06 19.03UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK      Backup: gmh@wdcc1.bnsc.rl.ac.uk
WORLD WIDE WEB                         http://www.theastronomer.org
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MESSIER 85 OPTICAL TRANSIENT OT2006-1 AND SUPERNOVA 2008S
On 2006 Jan 7, the Lick Observatory Supernova Search Team reported a mag 
19.3 new object in Messier 85 on unfiltered images.
Messier 85 (=NGC 4382) is a Hubble type S0 galaxy and member of Virgo 
cluster. It is believed the object was in M85 and projected 2.3 kpc from 
the centre of the galaxy.

J.L. Prieto, M.D. Kistler, K.Z. Stanek, T.A. Thompson, C.S. Kochanek, 
J.F. Beacom (Ohio State University) now report on The Astronomer's 
Telegram 1596 analysis of pre-discovery archival Spitzer data of this 
luminous transient in the Virgo galaxy Messier 85 obtained on 2005 Dec. 
28.72UT 8.8 days before the optical discovery of the transient reported 
by the KAIT supernova search.

We detect an infrared source at the position of the transient in all 
four IRAC bands (3.6-8.0 micron). The flux densities
of the source are (in micro Jy, errors approx. 10%): 176 (3.6 micron), 
206 (4.5 micron), 239 (5.8 micron), and 185 (8.0 micron). This bright 
infrared source is most likely associated with the transient, and not 
the progenitor, since it was not detected in archival Spitzer data of 
Messier 85 obtained in 2004. The transient is also detected in infrared 
images obtained with Spitzer 7 months
later, although the infrared fluxes have decreased by a factor of ~5 
from the earlier epoch. If we assume that the optical fluxes of the 
transient were roughly constant between the Spitzer pre-discovery 
detection and the initial post-discovery optical + NIR photometry 
obtained on Jan. 2006 by Kulkarni et al., the spectral energy 
distribution of the transient is well-fit by the sum of two black-bodies 
with T1~3900 K and T2~800 K.

The colder, infrared-bright component is likely due to reprocessing of 
UV/optical light by circumstellar dust. This bright, early infrared 
detection of the transient resembles the early spectral energy 
distribution of SN 2008S (found by Ron Arbour see TA E-Circular 2416: 
editor). Furthermore, the optical luminosity at discovery and the 
spectral properties of the Messier 85 transient are similar to SN 2008S 
and the luminous transient in NGC 300.

We propose that the transient in Messier 85, SN 2008S, and the luminous 
transient in NGC 300 form a new class of explosions of massive stars 
embedded in their own optically-thick dust.

Guy M Hurst