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Swift UVOT transient in M31

ATel #5669; R. Sturm, W. Pietsch, J. Greiner (MPE, Germany)
on 17 Dec 2013; 10:04 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 #: 5677, 5745

We report the discovery of a UV-transient (Swift J004249.9+411457) in monitoring observations of the central region of the Andromeda Galaxy (M 31) with the Ultra-Violet/Optical Telescope (UVOT) on board the Swift satellite. The source was detected first on 2013-12-01.02 UT. It is seen in a subsequent observations, but not in the previous observations. The source is located at RA=00:42:49.9 Dec=+41:14:57 (J2000, ePos=1"). 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              
                           [s]     [mag] 
00032702040    56619.35    4105    >20.10 
00032702041    56623.02    1189    >19.43 
00032702042    56627.02    2541    18.41±0.18 
00032702043    56631.03    3738    18.25±0.14 

There is no nearby bright (V>21.1 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, #3061, and #5528), the transient is likely explained by a new nova in M 31. The duration of the UV emission argues against 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.