Electronic Telegram No. 4175 Central Bureau for Astronomical Telegrams Mailing address: 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 2015ac IN UGC 12474 = PSN J23164332+3359476 Constantine Emmanouilidi, Thesaloniki, Greece, reports the discovery of an apparent supernova (unfiltered mag about 16.8) on CCD images (limiting mag about 17.5) taken by Stavros Koukioglou as part of the Greek Supernovae Survey Team on July 28.07 UT with a 0.30-m reflector at a private robotic observatory in Thessaloniki, Greece. The new variable is located at R.A. = 23h16m43s.32, Decl. = +33d59'47".6 (equinox 2000.0), which is 1" west and 3" north of the nucleus of PGC 70909 = UGC 12474. Nothing is visible at this position on Palomar Sky Survey images nor on an image taken (presumably with the discovery telescope) on 2007 July 18.04. The Greek images were posted at URL http://www.stellar-explosions.com/supernova-at-galaxy-pgc-70909/. The variable was designated PSN J23164332+3359476 when it was posted at the Central Bureau's TOCP webpage and is here designated SN 2015ac based on the spectroscopic confirmation reported below. Additional CCD magnitudes for 2015ac: July 29.070, 16.2 (S. Kiyota, Kamagaya, Japan; remotely with an iTelescope 0.32-m f/8 CDK astrograph + SBIG STXL-6303E camera at Nerpio, Spain; position end figures 43s.42, 51".9; image posted at website URL http://meineko.sakura.ne.jp/ccd/PSN_J23164332+3359476.jpg); 29.815, 18.1 (J. Brimacombe, Cairns, Australia; position end figures 43s.32, 47".6; image posted at URL https://www.flickr.com/photos/43846774@N02/19950647320/); Aug. 19.824, 16.7 (G. Masi and P. Catalano; remotely using a 43-cm telescope at Ceccano, Italy; position end figures 43s.39, 51".4); Sept. 5.019, 17.9 (V. Tsamis, near Athens, Greece; 40-cm f/10 Schmidt-Cassegrain reflector; position end figures 43s.44, 52".9). D. D. Balam, Dominion Astrophysical Observatory, National Research Council of Canada (NRCC); and M. L. Graham, Las Cumbres Observatory Global Telescope, University of California at Santa Barbara, report that a spectrogram (range 365-720 nm, resolution 0.3 nm) of PSN J23164332+3359476 = SN 2015ac, obtained on Aug. 5.36 UT with the 1.82-m Plaskett Telescope of the NRCC, shows it to be a normal type-Ia supernova near maximum light. Cross- correlation with a library of supernova spectra using the "Supernova Identification" code (Blondin and Tonry 2007, Ap.J. 666, 1024) suggests that 2015ac is most similar to the normal type-Ia supernova 1981B at two days prior to maximum light. Adopting the published redshift of the presumed host (Wegner et al. 1993, A.J. 105, 1251), they measure the photospheric velocity from the Si II 635.5-nm feature to be 11500 km/s. P. Ochner, S. Benetti, E. Cappellaro, N. Elias-Rosa, A. Pastorello, L. Tomasella, L. Tartaglia, G. Terreran, and M. Turatto, Osservatorio Astronomico di Padova, Istituto Nazionale di Astrofisica, report that an optical spectrogram (range 340-820 nm; resolution 1.4 nm) of PSN J23164332+3359476 = SN 2015ac, obtained on Aug. 5.99 UT with the Asiago 1.82-m Copernico Telescope, suggests that this variable is a type-Ia supernova. Assuming a recessional velocity of 5117 km/s for the host galaxy, UGC 12474 (Wegner at al. 1993, A.J. 105, 1251; via NED), a good match is found with the 1991bg- like type-Ia supernova 1986G at two or three days before maximum light. The expansion velocity of the ejected material, as inferred from the position of the absorption of the Si II 635.5-nm line, is about 10700 km/s. Classifications were done with GELATO (Harutyunyan et al. 2008, A.Ap. 488, 383) and SNID (Blondin and Tonry 2007, ApJ, 666, 1024). The Asiago classification spectra are posted at URL http://sngroup.oapd.inaf.it. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2015 CBAT 2015 November 16 (CBET 4175) Daniel W. E. Green