Electronic Telegram No. 2399 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 SUPERNOVA 2010gt IN ESO 187-21 L. A. G. Monard, Pretoria, South Africa, reports his discovery of an apparent supernova (magnitude about 18.0) on several unfiltered CCD images taken on Aug. 2.867 UT at the Bronberg Observatory. The new object, which was confirmed at magnitude about 17.7 on Aug 3.806, is located at R.A. = 20h51m22s.38, Decl. = -52d32'48".1 (equinox 2000.0), which is 3" east and 11" north of the galaxy core of ESO 187-21. Nothing is shown at the position in Digitized Sky Survey images down to red mag 20.5 or on the previous image of this galaxy taken at the Bronberg Observatory on 2010 July 7.067 (limiting mag 19.0) or on earlier images from there. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2010 CBAT 2010 August 3 (CBET 2399) Daniel W. E. Green