Electronic Telegram No. 3727 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 2013gn IN NGC 5557 = PSN J14182850+3630244 S. Nakano, Sumoto, Japan, reports the discovery by Koichi Itagaki (Teppo-cho, Yamagata, Japan) of an apparent supernova (mag 15.3) on an unfiltered CCD frame (limiting magnitude 17.5) taken on Nov. 16.830 UT using a 0.50-m f/6.8 reflector remotely at the Takanezawa station, Tochigi-ken. The new object is located at R.A. = 14h18m28s.50, Decl. = +36d30'24".4 (equinox 2000.0; reference stars from UCAC3 catalogue), which according to Nakano is 33".9 east and 47".4 north of the nucleus of the presumed host galaxy, NGC 5557. Itagaki writes that nothing is visible at this position on the Digitized Sky Survey (no details provided). The discovery image was posted at website URL http://www.k-itagaki.jp/images/5557.jpg. The variable was designated PSN J14182850+3630244 when it was posted at the Central Bureau's TOCP webpage and is here designated SN 2013gn based on the spectroscopic confirmation reported below. Additional CCD magnitudes for 2013gn: 2007 Feb. 19.715 UT, [19.5 (Itagaki; 0.60-m f/5.7 reflector at Yamagata); 20.756, 15.5 (Toshihide Noguchi, Katori, Chiba-ken, Japan; four stacked 30-s frames using a 0.23-m f/6.3 Schmidt-Cassegrain reflector + BITRAN BT-11E camera; limiting mag 17.0; position end figures 28s.56, 24".0; UCAC4 reference stars; offset 34" east, 48" north; communicated by Nakano; image posted at URL http://park8.wakwak.com/~ngc/images/PSNinNGC5557.jpg); 20.800, 15.4 (Itagaki; 0.50-m f/6.8 reflector remotely at the Takanezawa station; position end figures 28s.51, 24".2; communicated by Nakano); 21.496, 15.4 (Joseph Brimacombe, Cairns, Australia; remotely using a 51-cm RCOS telescope + STXL-6303 camera at the New Mexico Skies observatory near Mayhill, NM, U.S.A.; position end figures 28s.58, 24".3; image posted at website URL http://www.flickr.com/photos/43846774@N02/10990189383/); 21.501, R = 15.5 (T. Yusa, Osaki, Japan; remotely using an iTelescope 0.25-m f/3.4 astrograph + SBIG ST-10XME camera near Mayhill, NM; position end figures 28s.55, 24".1; UCAC4 reference stars; limiting magnitude 17.0; image posted at website URL http://space.geocities.jp/yusastar77/supernova/PSNinN5557_131121.htm). The type-Ia supernova 1996aa also appeared in NGC 5557 (cf. IAUC 6403). I. Ueno, R. Itoh, and K. S. Kawabata, Hiroshima; and M. Yamanaka, Kyoto University, obtained a low-resolution optical spectrum (range 480-900 nm) of PSN J14182850+3630244 = SN 2013gn on Nov. 22.8 UT with the 1.5-m Kanata telescope (+ HOWPol) at the Higashi-Hiroshima Observatory. A comparison with a library of supernova spectra using GELATO (Harutyunyan et al. 2008, A.Ap. 488, 383) suggests that the spectrum of 2013gn is consistent with that of the type-Ia supernova 2002dj at 24 days after B-band maximum. After correcting for the recession velocity of the host galaxy, the spectrum of 2013gn exhibits emission lines at 442, 540, 571, 610, and 821 nm, which are identified as Fe II, Cr II, Na I D, Si II 635.5-nm, and the Ca II infrared triplet, respectively. K. Ayani, Bisei Astronomical Observatory (BAO), Ibara, Okayama, Japan; and H. Yamaoka, Kyushu University, obtained a low-resolution spectrogram (range 400-800 nm, resolution 0.5 nm at H-alpha) of PSN J14182850+3630244 = SN 2013gn with the BAO 1.01-m telescope on Nov. 22.8 UT. The spectrum is that of a type-Ia supernova about 1 or 2 months after maximum. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2013 CBAT 2013 November 29 (CBET 3727) Daniel W. E. Green