Electronic Telegram No. 2574 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 APPARENT NOVA IN M31: M31N 2010-12a W. Zheng, A. Romadan, and N. Whallon, University of Michigan; J. Vinko, University of Szeged; R. Quimby, California Institute of Technology; S. B. Pandey, F. Yuan, and C. Akerlof, University of Michigan; P. Pasque and M. Verkinderen, Cousino High School; and J. C. Wheeler and E. Chatzopoulos, University of Texas, on behalf of the ROTSE collaboration, report the discovery of an optical transient in M31, located at R.A. = 0h40m24s.39, Decl. = +41o04'03".9 (equinox 2000.0; uncertainty < 1"), which is 26'.3 west and 12'.1 south from the core of M31, that was detected in unfiltered CCD images taken by the ROTSE-IIIb telescope at McDonald Observatory on Dec. 1.15 UT, both in co-added image and in four individual images at mag about 16.7. The object, designated 2010-12a, was not detected to a limiting magnitude of about 18.5 before and on Nov. 28. The quoted ROTSE magnitudes are calibrated relative to the USNO-B1.0 catalogue. A finding chart can be found at website URL http://www.rotse.net/rsvp/j004024.4+410404/ROTSE3-J004024.4+410404.jpg. Jiangao Ruan, Fangchenggang, Guangxi, China; and Xing Gao, Urumqi, Xinjiang, China, report their independent discovery of M31N 2010-12a at mag approximately 16.3 on two unfiltered 60-s survey CCD images (limiting mag about 19.5) taken by Xing Gao in the course of the Xingming Observatory Sky Survey around Dec. 1.5205 UT using a Celestron C14 Schmidt-Cassegrain telescope at Mt. Nanshan; they provide position end figures 24s.37 +/- 0s.01, 03".5 +/- 0".2. Additional magnitudes for M31N 2010-12a from Ruan and Gao: 1993 Oct. 21, [20.8 (Palomar Sky Survey, red N plate); 2010 Nov. 28, [19.5; 29, [19.5; Dec. 1.543, 16.1; 4.554, 16.0; 5.517, 16.0; 6.532, 16.2; 17.524, 16.3. Ruan and Gao have posted their images at website URL http://www.xjltp.com/XOSS/XM02JR/XM02JR.htm. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2010 CBAT 2010 December 8 (CBET 2574) Daniel W. E. Green