[IAUC] CBET 4175: 20151116 : SUPERNOVA 2015ac IN UGC 12474 = PSN J23164332+3359476

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                                                  Electronic Telegram No. 4175
Central Bureau for Astronomical Telegrams
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Prepared using the Tamkin Foundation Computer Network


SUPERNOVA 2015ac IN UGC 12474 = PSN J23164332+3359476
     Constantine Emmanouilidi, Thesaloniki, Greece, reports the discovery of
an apparent supernova (unfiltered mag about 16.8) on CCD images (limiting mag
about 17.5) taken by Stavros Koukioglou as part of the Greek Supernovae
Survey Team on July 28.07 UT with a 0.30-m reflector at a private robotic
observatory in Thessaloniki, Greece.  The new variable is located at R.A. =
23h16m43s.32, Decl. = +33d59'47".6 (equinox 2000.0), which is 1" west and 3"
north of the nucleus of PGC 70909 = UGC 12474.  Nothing is visible at this
position on Palomar Sky Survey images nor on an image taken (presumably with
the discovery telescope) on 2007 July 18.04.  The Greek images were posted at
URL http://www.stellar-explosions.com/supernova-at-galaxy-pgc-70909/.  The
variable was designated PSN J23164332+3359476 when it was posted at the
Central Bureau's TOCP webpage and is here designated SN 2015ac based on the
spectroscopic confirmation reported below.  Additional CCD magnitudes for
2015ac:  July 29.070, 16.2 (S. Kiyota, Kamagaya, Japan; remotely with an
iTelescope 0.32-m f/8 CDK astrograph + SBIG STXL-6303E camera at Nerpio,
Spain; position end figures 43s.42, 51".9; image posted at website URL
http://meineko.sakura.ne.jp/ccd/PSN_J23164332+3359476.jpg); 29.815, 18.1 (J.
Brimacombe, Cairns, Australia; position end figures 43s.32, 47".6; image
posted at URL https://www.flickr.com/photos/43846774@N02/19950647320/);
 Aug. 19.824, 16.7 (G. Masi and P. Catalano; remotely using a 43-cm telescope
at Ceccano, Italy; position end figures 43s.39, 51".4); Sept. 5.019, 17.9 (V.
Tsamis, near Athens, Greece; 40-cm f/10 Schmidt-Cassegrain reflector; position
end figures 43s.44, 52".9).

     D. D. Balam, Dominion Astrophysical Observatory, National Research
Council of Canada (NRCC); and M. L. Graham, Las Cumbres Observatory Global
Telescope, University of California at Santa Barbara, report that a
spectrogram (range 365-720 nm, resolution 0.3 nm) of PSN J23164332+3359476 =
SN 2015ac, obtained on Aug. 5.36 UT with the 1.82-m Plaskett Telescope of the
NRCC, shows it to be a normal type-Ia supernova near maximum light.  Cross-
correlation with a library of supernova spectra using the "Supernova
Identification" code (Blondin and Tonry 2007, Ap.J. 666, 1024) suggests that
2015ac is most similar to the normal type-Ia supernova 1981B at two days
prior to maximum light.  Adopting the published redshift of the presumed host
(Wegner et al. 1993, A.J. 105, 1251), they measure the photospheric velocity
from the Si II 635.5-nm feature to be 11500 km/s.

     P. Ochner, S. Benetti, E. Cappellaro, N. Elias-Rosa, A. Pastorello, L.
Tomasella, L. Tartaglia, G. Terreran, and M. Turatto, Osservatorio Astronomico
di Padova, Istituto Nazionale di Astrofisica, report that an optical
spectrogram (range 340-820 nm; resolution 1.4 nm) of PSN J23164332+3359476 =
SN 2015ac, obtained on Aug. 5.99 UT with the Asiago 1.82-m Copernico
Telescope, suggests that this variable is a type-Ia supernova.  Assuming a
recessional velocity of 5117 km/s for the host galaxy, UGC 12474 (Wegner at
al. 1993, A.J. 105, 1251; via NED), a good match is found with the 1991bg-
like type-Ia supernova 1986G at two or three days before maximum light.  The
expansion velocity of the ejected material, as inferred from the position of
the absorption of the Si II 635.5-nm line, is about 10700 km/s.
Classifications were done with GELATO (Harutyunyan et al. 2008, A.Ap. 488,
383) and SNID (Blondin and Tonry 2007, ApJ, 666, 1024).  The Asiago
classification spectra are posted at URL http://sngroup.oapd.inaf.it.


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
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                         (C) Copyright 2015 CBAT
2015 November 16                 (CBET 4175)              Daniel W. E. Green