Electronic Telegram No. 1775 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 2009dn IN PGC 35993 F. Yuan, University of Michigan; J. Vinko, University of Texas; R. Quimby, California Institute of Technology; D. Chamarro, M. D. Sisson, and C. Akerlof, University of Michigan; and J. C. Wheeler and E. Chatzopoulos, University of Texas, on behalf of the ROTSE collaboration, report the discovery of an apparent supernova (mag 17.5 +/- 0.2) in unfiltered CCD images taken on Apr. 12.78 UT with the 0.45-m ROTSE-IIId telescope at the TUBITAK National Observatory at Bakirlitepe, Turkey. The transient was discovered by subtracting a reference image constructed from images taken in 2008 (limiting mag 19.2), and it was also detected with the ROTSE-IIIb telescope at the McDonald Observatory at a similar magnitude on Apr. 11, 14, 15, and 16 (but not detected on Apr. 7.16 to a limiting magnitude of about 18.3); the photometric uncertainties are relatively large due to image subtraction. The new object is located at R.A. = 11h37m39s.33, Decl. = +46o57'11".3 (equinox 2000.0; uncertainty about 1"), which is 3".0 east and 2".5 south of the center of its apparent host galaxy, 2MASX J11373899+4657141. Given the redshift of the presumed host (z = 0.039, measured via the Sloan Digital Sky Survey) and the observed light curve, 2009dn is likely to be a supernova discovered around peak brightness. The location of 2009dn is shown in the chart posted at URL http://rotse.net/rsvp/j113739.3+465711/j113739.3+465711.jpg. Note that 2009dn is blended with the apparent host galaxy, due to the large pixel scale (3".3) of ROTSE-III. D. W. Bishop, Rochester, NY, U.S.A., reports that J. Brimacombe (Cairns, Australia) obtained three 600-s images of 2009dn remotely using a 51-cm telescope in New Mexico on Apr. 20.17, showing the new star at mag 16.9 and clearly resolved from the galaxy's nucleus. Bishop adds that nothing is visible at the position of 2009dn on a Digitized Sky Survey image from a Palomar Schmidt plate taken on 1953 Mar. 10. Brimacombe's image is posted at website URL http://www.RochesterAstronomy.org/sn2009/p35993s1.jpg. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2009 CBAT 2009 April 21 (CBET 1775) Daniel W. E. Green