Electronic Telegram No. 2487 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION CBAT Director: Daniel W. E. Green; Hoffman Lab 209; Harvard University; 20 Oxford St.; Cambridge, MA 02138; U.S.A. e-mail: cbatiau@eps.harvard.edu (alternate cbat@iau.org) URL http://www.cbat.eps.harvard.edu/index.html Prepared using the Tamkin Foundation Computer Network POSSIBLE NOVA IN M31: M31N 2010-10b Kamil Hornoch, Astronomical Institute, Ondrejov, reports his discovery of a possible nova in M31 on a co-added 990-s R-band CCD frame taken on Oct. 6.932 UT with the 0.65-m telescope at Ondrejov. The new object, designated M31N 2010-10b, is well visible on the co-added frame and faintly visible also on single images used for the co-added frame, but it is not present on numerous archival images taken at Lelekovice and Ondrejov. The object is visible also on four pre-discovery Ondrejov R-band CCD images taken between Aug. 19.055 and Sept. 20.777. Available magnitudes for M31N 2010-10b, measured by Hornoch: July 10.200, [22.0 (J. Corral-Santana and J. Casares, 2.54-m Isaac Newton Telescope + Sloan r' filter); Aug. 19.055, R = 20.0 +/- 0.3 (Hornoch and P. Hornochova, 0.65-m telescope at Ondrejov); 25.097, R = 19.6 +/- 0.25 (Hornoch and Hornochova); Sept. 14.128, R = 19.4 +/- 0.2 (Hornoch and Hornochova); 20.777, R = 19.5 +/- 0.2 (Hornoch and Hornochova); Oct. 6.932, R = 18.9 +/- 0.15 (Hornoch, 0.65-m telescope at Ondrejov); 7.767, R = 18.9 +/- 0.15 (Hornoch and M. Wolf, 0.65-m telescope at Ondrejov). M31N 2010-10b is located at R.A. = 0h42m41s.51, Decl. = +41o03'27".3 (equinox 2000.0), which is 32" west and 761" south of the center of M31. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2010 CBAT 2010 October 8 (CBET 2487) Daniel W. E. Green