Electronic Telegram No. 2754 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 PSN J17592296+0617267 IN NGC 6509 Further to CBET 2745, J. Kelly, S. B. Cenko, W. Li, and A. V. Filippenko report the LOSS discovery of an apparent supernova on unfiltered KAIT images. The object was designated PSN J17592296+0617267 when posted at the Central Bureau's TOCP webpage. The discovery observation is tabulated below. 2011 UT R.A. (2000.0) Decl. Mag. Offset June 24.37 17 59 22.96 + 6 17 26.7 18.5 34".4 W, 13".6 N Additional CCD magnitudes (unfiltered unless noted otherwise) for PSN J17592296+0617267: a co-added frame from June 2 to 19 UT, [19.8 (KAIT); June 24.37, 18.6 (KAIT); 25.426, 18.2 (J. Brimacombe, Cairns, Australia; position end figures 23s.03, 25".7); 25.925, 18.2 (Federica Luppi, Schiaparelli Observatory, Varese, Italy, 0.36-m f/7.9 reflector + Bessell R filter; position end figures 22s.99, 26".1); 26.333, 18.7 (Brimacombe; position end figures 22s.99, 26".5). Luppi adds that nothing is visible at this position on Digitized Sky Survey red, blue, and infrared images (limiting red mag about 19.5 on 1991 June 16); her image is posted at website URL http://www.astrogeo.va.it/pub/TOCP/PSN_N6509.jpg. Brimacombe's image from June 25 is posted at http://www.flickr.com/photos/43846774@N02/5868925873/. Brimacombe's image from June 26 is posted at the following website URL: http://www.flickr.com/photos/43846774@N02/5875580438/. J. M. Silverman, S. B. Cenko, P. E. Nugent, and A. V. Filippenko, University of California, Berkeley, report that inspection of a CCD spectrum (range 340-1000 nm), obtained on June 29 UT with the 10-m Keck I telescope (+ LRIS), shows that PSN J17592296+0617267 very closely resembles SN 2008S at early phases (Smith et al. 2009, Ap.J. 697, L49). Strong, intermediate-width (FWHM roughly 1000 km/s) hydrogen Balmer and Ca II near-infrared triplet emission lines are superposed on a relatively featureless continuum, and there are very narrow (unresolved) prominent [Ca II] emission lines as well. Thus, this object is most likely a "supernova impostor" resembling a type-IIn supernova, but resulting from the outburst of a luminous blue variable star. Note that the Ca II H and K absorption lines are extremely strong, yet Na I D absorption is weak, suggesting that the Ca II lines are of circumstellar origin and may well be variable; further spectroscopic monitoring is encouraged. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2011 CBAT 2011 June 30 (CBET 2754) Daniel W. E. Green