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Swift UVOT transient in M 31

ATel #5528; R. Sturm, F. Haberl, W. Pietsch, J. Greiner (MPE, Germany)
on 30 Oct 2013; 16:27 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 #: 5554, 5569, 5669

We report the discovery of a UV-transient (Swift J004304.9+411630) in a monitoring observation (ObsID 00032702034) of the central region of the Andromeda Galaxy (M 31) with the Ultra-Violet/Optical Telescope (UVOT) on board the Swift satellite. The transient is visible in the last two exposures, but not in the first two exposures, thus constraining the appearance between 2013-10-30.07 UT and 2013-10-30.28 UT. The source is located at RA=00:43:04.90 Dec=+41:16:30.1 (J2000, ePos=0.44", 90% confidence level). Light curve information for filter uvw1 (central wavelength: 260 nm) is given in the table below (Vega system, 1σ statistical uncertainties or 3σ upper limits, respectively). 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             Note 
                            [s]      [mag] 
00032702034[1]   56595.01   1196     >19.89 
00032702034[2]   56595.07   1314     >19.90           (unstable pointing) 
00032702034[3]   56595.28   792      17.73±0.12 
00032702034[4]   56595.35   727      17.76±0.12 

There is no nearby bright (V>21.7 mag) object in the catalogue of Massey et al. (2006, AJ 131, 2478) and 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 ). Because many UV transients in M 31 have been identified with optical novae, 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.