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Swift UVOT transient in M 31

ATel #5384; R. Sturm, F. Hofmann, W. Pietsch, J. Greiner (MPE, Germany)
on 11 Sep 2013; 14:01 UT
Distributed as an Instant Email Notice Novae
Credential Certification: Richard Sturm (rsturm@mpe.mpg.de)

Subjects: Ultra-Violet, Nova, Transient

Referred to by ATel #: 5385, 5503

We report the discovery of a UV-transient (Swift J00431492+4119130) in a monitoring observation of the central region of the Andromeda Galaxy (M 31) with the Ultra-violet/Optical Telescope (UVOT) on board the Swift satellite (ObsID 00035336120, starting 2013-09-11.01 UT). The source is located at RA 00h 43m 14.93s, Dec +41d 19' 13.0" (J2000, ePos=0.5", 90% confidence level). Light curve information for filters uvw1 (central wavelength: 260 nm) and uvm2 (225 nm) is given in the table below (Vega system, 1σ statistical uncertainties). 3σ upper limits are derived from previous M 31 Swift monitoring observation before the detection. All magnitudes are on the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) and have not been corrected for extinction.

 ObsID           MJD        Exp   uvm2          uvw1      
                            [s]   [mag]         [mag] 
 00035336106     56450.75  3309   >21.09 
 00035336118     56535.08  3798                 >20.82  
 00035336120     56546.02  1664   19.36±0.20 

There is no report of a recent detection of an optical nova or a historical nova (see http://www.mpe.mpg.de/~m31novae/opt/m31/M31_table.html ) for the position of the transient. Because many UV transients in M 31 have been identified with optical novae in M 31, also with UV emission preceding the optical detection (see e.g. ATels #2713, #2727, and #3061), the transient is likely explained by a new nova in M 31. However, with the current data, we cannot exclude other possibilities like a flare star.

In order to investigate the nature of the newly detected UV transient, spectroscopic observations in the optical are encouraged.

We would like to thank the Swift Team for making these observations possible, in particular N. Gehrels, the duty scientists, as well as the science planners.