Electronic Telegram No. 2126 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 2010G W. Zheng, University of Michigan; E. Chatzopoulos, University of Texas; J. Vinko, University of Szeged; R. Quimby, California Institute of Technology; F. Yuan, D. Chamarro, M. D. Sisson, N. Whallon, C. Akerlof, and S. B. Pandey, University of Michigan; J. C. Wheeler, University of Texas; and G. H. Marion, Texas A&M University and University of Texas, on behalf of the ROTSE collaboration, report the discovery of a new supernova (mag about 19.4) in unfiltered images taken on Jan. 9.46 UT with the 0.45-m ROTSE-IIIb telescope at McDonald Observatory. The new object, which was observed again on Jan. 10.46 at mag 19.1 and on Jan. 13.39 at mag 19.5, is located at R.A. = 12h25m10s.01, Decl. = +45o19'43".9 (equinox 2000.0; uncertainty about 1"), which is 0".5 west and 1".5 south of the center of the host galaxy, SDSS J122510.05+451945.3; a finding chart for the object can be found at website URL http://www.rotse.net/rsvp/j122510.0+451944/j122510.0+451944.jpg. A spectrum obtained on Jan. 12.3 with the 9.2-m Hobby-Eberly Telescope (+ Marcario Low-Resolution Spectrograph) by S. C. Odewahn shows 2010G to be a normal type-Ia supernova at maximum. According to SNID (Blondin and Tonry 2007, Ap.J. 666, 1024), the spectrum best resembles that of SN 1998aq at one day before maximum brighness, at a redshift of z = 0.115. The photometric measurements are also consistent with a normal type-Ia supernova near maximum at this redshift. The rest-frame photospheric velocity, estimated from the minimum of the Si II 635.5-nm feature is about 10000 km/s. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2010 CBAT 2010 January 16 (CBET 2126) Daniel W. E. Green