Electronic Telegram No. 2711 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 2011cb IN PGC 69707 = PSN J22470700-6449430 Greg Bock, Windaroo, Queensland, Australia, reports the discovery by Stuart Parker (Oxford, Canterbury, New Zealand) of an apparent supernova (mag 14.9) on an unfiltered CCD image obtained on Apr. 29.68 UT with a 35-cm Celestron C14 f/6.3 reflector (+ ST10 CCD camera) in the course of the Backyard Observatory Supernova Search. The new object (which was designated PSN J22470700-6449430 when posted at the Central Bureau's TOCP webpage and is here designated SN 2011cb based on the spectroscopic report below) was reported by Stuart to be located at R.A. = 22h47m07s.00, Decl. = -64d49'43".0 (equinox 2000.0). Bock measured 2011cb to be at position end figures 07s.49, 43".4, which is 8" east and 7" north of the nucleus of the galaxy PGC 69707. Nothing is visible at this position on red and infrared images from the Digitized Sky Survey (limiting mag > 19). Additional magnitudes for 2011cb: Apr. 30.508, 15.1 (Stuart; measured by Bock); 30.808, 15.2 (Joseph Brimacombe, Cairns, Australia, 30-cm reflector + STL6K camera + red filter; position end figures 06s.9, 43".3); May 1.800, 15.2 (Brimacombe). Brimacombe's Apr. 30 image is posted at the following website URL: http://www.flickr.com/photos/43846774@N02/5676226310/; his May 1 image is posted at http://www.flickr.com/photos/43846774@N02/5679218216/. M. Stritzinger, Oskar Klein Centre, Stockholm University; N. Morrell, Las Campanas Observatory; and G. Folatelli, IPMU, University of Tokyo, report on spectra (range 360-1011 nm) of SN 2011cb taken on May 1.3 and 2.3 UT by B. Madore of the Carnegie Observatories. Both spectra were obtained at Las Campanas Observatory with the 2.5-m du Pont telescope (+ WFCCD), and they show that 2011cb is a type-IIb supernova. Comparison with a library of supernova spectra via the Supernova Identification tool (SNID; Blondin and Tonry, 2007, Ap.J. 666, 1024) shows that 2011cb is very similar to SN 1997dd as observed on 1997 Sept. 6 and that it also resembles other type-IIb events around maximum light. The spectra exhibit prevalent P-Cyg absorption lines associated with the the Balmer series and Ca II. Additional features related with He I are visible, most noticeably He I 587.6-nm, which is probably blended with Na I D. Features related to the Fe II multiplet 42 are also discernible. Adopting a host-galaxy recession velocity of 2366 km/s for PGC 69707 (Koribalski et al. 2004, A.J. 128, 16), expansion velocities of 13000 km/s and 12500 km/s for the first and second epochs, respectively, are obtained from the absorption minimum of H-alpha. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2011 CBAT 2011 May 4 (CBET 2711) Daniel W. E. Green