Electronic Telegram No. 2358 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION CBAT Director: Daniel W. E. Green; Room 209; Dept. of Earth and Planetary Sciences; Harvard University; 20 Oxford St.; Cambridge, MA 02138; U.S.A. e-mail: cbat@iau.org; cbatiau@eps.harvard.edu URL http://www.cfa.harvard.edu/iau/cbat.html APPARENT NOVA IN M31: M31N 2010-07a Kamil Hornoch, Astronomical Institute, Ondrejov; and Petr Zasche, Astronomical Institute, Charles University, Prague, report their discovery of an apparent nova in the galaxy M31 on a co-added 2160-s R-band CCD frame taken by Zasche on July 8.060 UT with the 0.65-m telescope at Ondrejov. The new object is well visible on single images used for the co-added frame and faintly visible on a pre-discovery co-added R-band CCD frame taken by Hornoch with the same instrumentation on July 7.036 UT, but it is not present on numerous archive images taken at Lelekovice and Ondrejov. M31N 2010-07a is located at R.A. = 0h43m20s.13, Decl. = +41o21'23".7 (equinox 2000.0), which is 403" east and 315" north of the center of M31. Available R-band magnitudes for M31N 2010-07a, as measured by Hornoch: July 4.005 UT, [21.1 (K. Hornoch, 0.65-m telescope at Ondrejov); 4.956, [20.9 (Hornoch); 7.036, 20.2 +/- 0.3 (Hornoch); 8.060, 18.25 +/- 0.1 (P. Zasche, 0.65-m telescope at Ondrejov). M. Henze, Max-Planck-Institut fuer Extraterrestrische Physik, (MPE); V. Burwitz, MPE and Observatorio Astronomico de Mallorca (OAM); W. Pietsch, MPE; J. Rodriguez, OAM; and C. A. Haswell, S. Holmes, U. Kolb, and R. Lucas, The Open University (TOU), confirm M31N 2010-07a after being notified by Hornoch. The new object is visible at a corresponding R magnitude of 18.4 on two stacks of five 120-s unfiltered CCD images obtained with the TOU/OAM PIRATE 0.35-m f/11 Schmidt-Cassegrain telescope (+ SBIG STL-1001E CCD camera) at Costitx, Mallorca, Spain, on July 8.02 and 8.07 UT, with position end figures 20s.11, 23".7 (uncertainty 0".3), which is 403" east and 314" north of the core of M31. No object is visible at this position on a PIRATE image from June 26.08 (limiting R magnitude 19.0). M31N 2010-07a was already active during an observation with the UltraViolet/Optical Telescope (UVOT) onboard the Swift satellite one day before the optical discovery. The 3815-s UVW1-filter observation (range 181-321 nm) starting on July 7.07 UT shows M31N 2010-07a at mag 20.6 +/- 0.3 at a position consistent with the coordinates of the optical source; no source is visible at this position in an earlier UVW1-filter observation starting on June 24.02 (limiting magnitude 21.0). The optical magnitudes were obtained from a photometric solution using R magnitudes of the Local Group Survey M31 catalogue (Massey et al. 2006, A.J. 131, 2478); the ultraviolet magnitudes are on the UVOT photometric system (Poole et al. 2008, MNRAS 383, 627) and have not been corrected for extinction. The Swift team is thanked for scheduling the Target-of-Opportunity observations. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2010 CBAT 2010 July 8 (CBET 2358) Daniel W. E. Green