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Swift UVOT discovery of a M 31 nova candidate

ATel #5256; >R. Sturm, W. Pietsch, F. Hofmann, J. Greiner (MPE, Germany)
on 7 Aug 2013; 16:01 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 #: 5260

We report the discovery of a UV-transient (PNV J00422137+4113004) 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 00035336114, starting 2013-08-07.11 UT). The source is located at RA 00h 42m 21.37s, Dec +41d 13' 00.4" (J2000, ePos=0.5", 90% confidence level). Light curve information is given in the table below (Vega system, 1σ statistical uncertainties). A 3σ upper limit is derived from the last M 31 Swift 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    uvw1      
                            [s]    [mag] 
 00035336113     56503.287  3936   >20.64 
 00035336114[1]  56511.106  1336   16.31±0.03 
 00035336114[2]  56511.173  1396   16.24±0.03 
 00035336114[3]  56511.367  1354   16.39±0.03 

The source 2MASS 00422116+4113007 (angular separation: 2.3", Ks=15.9 mag) is unlikely related to the transient and the outburst duration (>6.2 h) is atypical for a flare of a Galactic star. 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.

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.