Electronic Telegram No. 1172 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A. IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions) CBAT@CFA.HARVARD.EDU (science) URL http://www.cfa.harvard.edu/iau/cbat.html SUPERNOVA 2007sr IN NGC 4038 A. J. Drake, S. G. Djorgovski, R. Williams, A. Mahabal, and M. J. Graham, California Institute of Technology; E. Christensen, Gemini Observatory; and E. C. Beshore and S. M. Larson, Lunar and Planetary Laboratory, University of Arizona, report the discovery of an apparent supernova (mag approximately 12.9) in four 30-s CCD exposures (limiting mag about 20) taken in the course of the Catalina Sky Survey (CSS) on Dec. 18.53 UT using the 0.7-m f/1.9 Schmidt telescope (+ 4000x4000 camera). The new object, now designated 2007sr, is located at R.A. = 12h01m52s.80, Decl. = -18o58'21".7 (equinox 2000.0), and appears on one of the arms (or "antennae") emanating from NGC 4038 (which is interacting with the galaxy NGC 4039). Nothing appears at this position in co-added CSS images from 2006 Dec. 21 (limiting mag about 21.5); also, nothing definite appears on mutliple exposures obtained on 1999 Feb. 22 with the Hubble Space Telescope (+ WFPC2 + F814W filter), though it is possible that a precursor as bright as I-band mag about 23 is present therein. CSS images of 2007sr are posted at this website URL: http://www.cacr.caltech.edu/~ajd/CSS_ATEL/712180180624111439.html E. Guido and G. Sostero (Remanzacco, Italy) write that five co-added 60-s CCD frames taken remotely with a 0.25-m f/3.4 reflector located near Mayhill, NM, U.S.A., on Dec. 19.42 show 2007sr at position end figures 52s.80, 21".8 and magnitudes B = 13.20, V = 12.85, R = 12.80 (uncertainty +/- 0.05 magnitude in each color). Their image is posted at this website URL: http://www.fototime.com/%7B885F3FF0-0039-47A9-A815-71150CC0EC7B%7D/picture.JPG W. Li, Unversity of California at Berkeley, reports that 2007sr appears at mag 12.9 and position end figures 52s.79, 21".3 on KAIT images (cf. CBET 1179) taken on Dec. 19.52 UT. SNe 1921A, 1974E (cf. IAUC 2653), and 2004gt (cf. IAUC 8454, 8456) also appeared in NGC 4038. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2007 CBAT 2007 December 19 (CBET 1172) Daniel W. E. Green