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Swift UV detection and optical confirmation of a nova candidate in M 31

ATel #2713; W. Pietsch, M. Henze, V. Burwitz (Max-Planck-Institut fuer extraterrestrische Physik, MPE), A. Liakos (Dept. Physics, University of Athens), D. Hatzidimitriou (Dept. of Physics, University of Crete) and P. Niarchos (Dept. Physics, University of Athens)
on 1 Jul 2010; 16:17 UT
Credential Certification: Wolfgang Pietsch (wnp@mpe.mpg.de)

Subjects: Optical, Ultra-Violet, Nova

Referred to by ATel #: 2787, 3061, 3712, 5256, 5384, 5528, 5669

We report the detection of a nova candidate in M 31 using observations with the UltraViolet/Optical Telescope (UVOT) on board the Swift satellite. The object was serendipitously detected in the UVW1 filter (181-321nm) UVOT observation 00031255018 with 4333 s exposure starting on 2010-06-24.02 UT with a magnitude of 19.5+-0.2. The position for the nova candidate is RA = 00h42m55s.56, Dec = +41d19'25".5 (J2000, accuracy of 1.0"), which is 127" east and 197" north of the core of M 31. The source is clearly detected in the individual images. In the UVW1 filter Swift observation 00031255014 starting on 2010-06-12.04 UT (4161 s exp.) and in the U filter Swift observation 00031255017 starting on 2010-06-21.29 UT (1330 s exp.) no object was detected at the position with a limiting magnitude of 20.5 and 19.7 (3 sigma), respectively. All magnitudes are on the UVOT photometric system (Poole et al. 2008, MNRAS, 383, 627) and have not been corrected for extinction.
The possible nova was confirmed on a 10x60s stacked CCD image without filter obtained at a 40-cm Cassegrain telescope with a focal reducer (F/5.1) equipped with a 2184 x 1472 pixel ST-10XME CCD camera (pixel size 6.8 microns square) at the Athens University Observatory, Greece, on 2010-07-01.082 UT. We find a magnitude of 17.8 and position end figures of 55s.62, 25".7 (J2000, accuracy of 0.5") fully consistent with the position of the Swift source. The magnitude given was obtained from a photometric solution using R magnitudes of the Local Group Survey M 31 catalogue (Massey et al. 2006).
The nova candidate is visible in the UV filter already several days before the detection in the optical. This is similar to novae M31N 2009-08a (see ATel #2274) and M31N 2010-01b (ATel #2435). The earlier UV detection may either indicate that the actual optical outburst of the nova has been missed and a re-brightening of the nova had been misidentified as the outburst or a higher sensitivity for UV detection due to lower background in the central area of M 31.
We acknowledge the use of public data from the Swift data archive.