Electronic Telegram No. 2603 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 SUPERNOVA 2010lm G. Pignata and M. Cifuentes, Universidad Andres Bello; J. Maza, M. Hamuy, R. Antezana, L. Gonzalez, R. Cartier, F. Forster, S. Silva, and F. Carrasco, Universidad de Chile; P. Gonzalez, Pontificia Universidad Catolica de Chile; B. Conuel, Wesleyan University; G. Folatelli, IPMU, University of Tokyo; and D. Reichart, K. Ivarsen, J. Haislip, A. Crain, D. Foster, M. Nysewander, and A. LaCluyze, University of North Carolina at Chapel Hill, on behalf of the CHASE project, report the discovery of an apparent supernova (mag approximately 18.1 +/- 0.5) on an unfiltered image taken on Dec. 20.22 UT with the 0.41-m 'PROMPT 4' telescope located at Cerro Tololo. The new object, which is also present at mag approximately 17.0 +/- 0.3 in an image taken on Dec. 22.25, is located at R.A. = 10h03m57s.35 +/- 0".2, Decl. = -27o38'30".3 +/- 0".2 (equinox 2000), which is about 2".8 west and 0".9 south of the center of the presumed host galaxy. Nothing is visible at this position on archival images taken on Dec. 9.31 (limiting mag 18.5) and in a stack of seventeen 400-s images taken between 2009 Nov. 8.33 and 2010 Nov. 25.26 (limiting mag 20.7). NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2010 CBAT 2010 December 23 (CBET 2603) Daniel W. E. Green