Electronic Telegram No. 4229 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 2015bh IN NGC 2770 = PSN J09093496+3307204 = PSN J09093506+3307221 S. Howerton, Arkansas City, KS, USA; A. J. Drake, S. G. Djorgovski, A. Mahabal, M. J. Graham, and R. Williams, California Institute of Technology; M. Catelan, Pontificia Universidad Catolica de Chile; and E. Christensen and S. M. Larson, Lunar and Planetary Laboratory, University of Arizona, report the Catalina Real-time Transient Survey discovery of a transient source in public images from the Catalina Sky Survey (CSS). SN 2015 UT R.A. (2000.0) Decl. Mag. Offset 2015bh Feb. 7.39 9 09 34.96 +33 07 20.4 19.1 15".8 E, 4".4 S The variable was designated PSN J09093496+3307204 when it was posted at the Central Bureau's TOCP webpage and is here designated SN 2015bh based on the spectroscopic confirmation reported below. An independent discovery was reported by Z.-j. Xu (Nanjing, Jiangsu, China) and X. Gao (Urumqi, Xinjiang, China), with the object reported at mag approximately 17.8 on one 40-s survey image (limiting mag about 18.0) taken by Gao in the course of the Xingming Sky Survey on Apr. 7.737 UT with a Celestron C14 Schmidt-Cassegrain telescope; the position end figures were measured to be 35s.03 +/- 0s.03, 21".9 +/- 0".3 (with offset 15".2 east and 2".6 south of the center of NGC 2770, and when they posted the object as a new discovery on the TOCP, it was automatically assigned the designation PSN J09093496+3307204. Additional CCD magnitudes for 2015bh: 1998 Apr. 21, [19.6 (Gao; Digitized Sky Survey); 2014 Dec. 15, [21.0 (CSS); 24.32, 20.3 (CSS); 2015 Jan. 21.35, 19.5 (CSS); 22.38, 19.5 (CSS); Feb. 8.144, 19.9 (Howerton; 0.28-m f/5 reflector; image posted at URL https://www.flickr.com/photos/watchingthesky/15846899274); 17.825, 19.6 (G. Masi; remotely using a 43-cm telescope at Ceccano, Italy; position end figures 35s.11, 21".5); Mar. 22, [19.0 (Gao); 24, [18.7 (Gao); Apr. 9.716, 18.0 (Gao); 9.717, 18.3 (Gao); May 16.928, 16.0 (R. Arbour, South Wonston, U.K.; position end figures 35s.11, 22".2). The type-I supernovae 1999eh (cf. IAUC 7282) and 2007uy (IAUC 8908) also appeared in NGC 2770. A. de Ugarte Postigo, Instituto de Astrofisica de Andalucia, Consejo Superior de Investigaciones Cientificas (CSIC), Granada, Spain, and Dark Cosmology Centre, Niels Bohr Institute, Copenhagen; C. C. Thoene, Instituto de Astrofisica de Andalucia, CSIC; G. Leloudas, Weizmann Institute of Science, Rehovot, Israel, and Niels Bohr Institute, Copenhagen; and F. Aceituno, Instituto de Astrofisica de Andalucia, CSIC, report that they found PSN J09093496+3307204 = PSN J09093506+3307221 = SN 2015bh to be unexpectedly bright at magnitude R = 16.0 on May 15.865 UT in images obtained with the 0.9-m telescope at Sierra Nevada Observatory (Granada, Spain), the object's position end figures being measured as 35s.12, 21".3 (offset 16" east, 4" south of the center of the galaxy NGC 2770); an image taken on May 6 with the 1.5-m telescope at Sierra Nevada Observatory showed the object fainter at R = 18.5. After the object had been first announced by Howerton, Drake et al. (see above), it was determined to be an eruption of a luminous blue variable (e.g., see Elias-Rosa et al. 2015, as posted at website URL http://www.astronomerstelegram.org/?read=7042; and de Ugarte Postigo et al. 2015, website URL http://www.astronomerstelegram.org/?read=7409). The absolute magnitude of the object corresponds to -16.6, assuming a distance of 27 Mpc for NGC 2770; this brightness is unusually luminous for an LBV in outburst but is fully compatible with supernova explosions. An optical spectrogram (resolution 1000; wavelength range 360-1000 nm) was obtained on May 16.89 UT with the Gran Telescopio Canarias at La Palma. The spectrum is typical of type-IIn supernovae, demonstrating prominent Balmer lines with a narrow component superimposed on a broader asymmetric component. The full- width-at-half-maximum of the H-alpha line is about 1800 km/s. He I lines (587.6-, 667.8-, and 706.5-nm) are also detected in emission, and the strongest line (He I 587.6-nm) clearly shows a double component with a narrow line superimposed on a broader base. On the blue side of H-beta, they observe a feature that they identify as He II 468.6-nm, a line that is often observed in spectra of supernovae, obtained early after explosion, when the temperature is high. All features are superimposed on a blue continuum. It is therefore quite possible from this discovery that the LBV has evolved into a supernova. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2015 CBAT 2015 December 22 (CBET 4229) Daniel W. E. Green