Electronic Telegram No. 4123 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION CBAT Director: Daniel W. E. Green; 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 2015M = PSN J13003230+2758411 On May 13, S. Nakano (Sumoto, Japan) reported the discovery of an apparent supernova (mag 17.2) by K. Itagaki (Teppo-cho, Yamagata, Japan) on an unfiltered CCD frame (limiting magnitude 19.5) taken on May 13.5196 UT using a 0.60-m f/6.7 reflector. Itagaki measured the position of the new object to be R.A. = 13h00m32s.30, Decl. = +27d58'41".1 (equinox 2000.0), which is close the center of a galaxy in the image. Itagaki posted his discovery image at URL http://www.k-itagaki.jp/images/5-psn.jpg. The variable was designated PSN J13003230+2758411 when it was posted at the Central Bureau's TOCP webpage and is here designated SN 2015M based on the spectroscopic confirmation reported below. Two additional independent discoveries were reported to the Bureau after the TOCP posting: the first reported on May 14 by J. R. Lucey on images taken on May 12 with the University of Durham's 35-cm DRACO2 telescope (noting that the variable was not visible on images taken with the same telescope on May 7 (no limiting magnitude provided), and the second reported on May 24 by Tomoki Morokuma, Institute of Astronomy, University of Tokyo (with colleagues Nozomu Tominaga, Konan University; Masaomi Tanaka, National Astronomical Observatory of Japan; Dmitry Tsvetkov and Nickolay Pavlyuk, Sternberg Astronomical Institute, Lomonosov Moscow State University; Yuki Sarugaku and Ji-an Jiang, University of Tokyo; Yoshihiko Saito, Tokyo Technology of Institute; Masafumi Yagi, National Astronomical Observatory of Japan; Takumi Shibata, Konan University; Katsuhiko Mameta, Hyogo, Japan; and Masanori Takeishi, Hokkaido, Japan), on behalf of the Kiso Supernova Survey (KISS) collaboration, from a g-band CCD image (limiting mag 20.6) taken on May 10.54 with the Kiso Wide Field Camera (field-of-view 2.1 deg x 2.1 deg) on the 1.05-m Kiso Schmidt telescope. Morokuma et al. note that images obtained with the Advanced Camera for Surveys onboard the Hubble Space Telescope in the ACS Coma Cluster Treasury survey show a faint possible host galaxy (COMAi13032.301p275841.02; magnitude [F814W] = 25.2; Hammer et al. 2010, Ap.J. Suppl. 191, 143) at the position of 2015M. Additional CCD magnitudes for 2015M: Apr. 21.632 UT, [19.0 (Itagaki); May 10.54, 18.3 (Morokuma et al.; position end figures 32s.33, 41".0); May 10.756, 17.6 (Zhijian Xu and Xing Gao; Celestron C14 Schmidt-Cassegrain telescope; pre-discovery image taken in the course of the Xingming Sky Survey; position end figures 32s.34, 41".3; image posted via website URL http://tinyurl.com/pzb6nth); May 12, 16.8 (Lucey; position end figures 32s.27, 41".1; May 7 and 12 images posted via URL http://tinyurl.com/py6qlf3); May 13.929, 16.7 (N. James, Chelmsford, Essex, England; Celestron 11 telescope; position end figures 32s.32, 41".0; UCAC-4 reference stars; image viewable via website URL http://tinyurl.com/ox3vww7); May 14.126, B = 16.8, V = 17.0, I_ c = 17.0 (S. Kiyota, Kamagaya, Japan; remotely with an iTelescope 0.43-m f/4.5 CDK astrograph + FLI-PL6303E CCD camera near Mayhill, NM, USA; position end figures 32s.34, 41".1); May 14.921, 16.2 (G. Masi and P. Catalano; remotely using a 43-cm telescope at Ceccano, Italy; position end figures 32s.32, 41".2); May 16.529, 16.3 (T. Yusa, Y. Suzuki, N. Wada, S. Tsunoda, S. Sasaki, and H. Goto; three stacked 120-s frames taken using a 0.30-m f/7 Cassegrain reflector + SBIG ST-1001E camera at the Osaki Lifelong Learning Center, Japan; limiting mag 19.0; image posted posted at website URL http://space.geocities.jp/yusastar77/supernova/PSNinIC4041_150516.htm); May 16.769, 16.1 (P. Corelli, Pagnacco, Italy; 0.4-m telescope; image posted at https://www.flickr.com/photos/52195265@N06/17599300538/in/dateposted-public/); May 17.456, 16.5 (T. Noguchi, Katori, Chiba-ken, Japan; 0.23-m f/6.3 Schmidt- Cassegrain reflector; position end figures 32s.31, 41".0; image posted at URL http://park8.wakwak.com/~ngc/images/PSN_J13003230_2758411.jpg; communicated by Nakano). Paolo Mazzali, Andrzej Piascik, Chris Ashall, and Simon Prentice, Liverpool John Moores University; Francesco Taddia, Stockholm University; Maximilian Stritzinger and Ditte Slumstrup, Aarhus University; and Maria R. Drout and Philip S. Cowperthwaite, Harvard University, report that an optical spectrograms of SN 2015M were obtained on May 13 UT with the SPRAT instrument on the Liverpool telescope, on May 15 with both the Andalucia Faint Object Spectrograph and Camera on the Nordic Optical Telescope and the IMACS instrument on the Magellan-Baade telescope. Cross-correlation with a library of supernova spectra using the "Supernova Identification" code (SNID; Blondin and Tonry 2007, Ap.J. 666, 1024) for all these spectra shows good matches with a pre-maximum 1991T-like type-Ia supernovae, showing high ionization lines of Fe II and Fe III. The redshift estimated from the spectral fitting of the supernova spectra is roughly consistent with the Coma cluster redshift. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2015 CBAT 2015 July 27 (CBET 4123) Daniel W. E. Green