Spitzer Space Telescope - Directors Discretionary Time Proposal #276


A new class of transients

Principal Investigator: Shrinivas Kulkarni
           Institution: Caltech

Co-Investigators: 
A. Rau, Caltech                                                       
E. Ofek, Caltech                                                      
L. Yan, SSC                                                           

Science Category: Nearby Galaxies (z<0.05, v_sys<15,000 km/s) 
 Observing Modes: IracMap IrsPeakupImage 
  Hours Approved: 9.3 

Abstract:
The two most common astronomical explosions are novae and supernovae.
It has long been noted that there is a curious dearth of explosive
events with brightness in between these two classes.  We have
uncovered and followed up such an event located in the outskirts of
the nearby lenticular galaxy Messier 85.  This object, hereafter M85
OT 2006-1, peaked at an absolute R-band magnitude of -13 and released
~10E47 erg over the first two month.  The optical light curve showed
steady emission for about 100  days together with a shift of the peak
frequency from optical to near-IR.  This resembles two other
mysterious transients, the enigmatic M31-RV in M31 as well as V838 Mon
in the Milky Way.  However, M85 OT 2006-1 is even more challenging to
understand given that it is more luminous by an order of magnitude.
One possibility for their origin is the merger of a star with a
companion, either another star or brown dwarf.  Based on the evolution
of V838 Mon, the spectrum of M85 OT 2006-1 can be expected to shift
further to the thermal infrared.  Here we propose to use IRAC for deep
imaging from 3.6 to 8 microns in order to monitor the IR evolution of
the source and diagnose the mass and geometry of the ejecta.