[IAUC] CBET 3607: 20130728 : SUPERNOVAE 2012im AND 2013ek IN NGC 6984

Sab Jul 27 21:42:12 ART 2013

                                                  Electronic Telegram No. 3607
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 en eps.harvard.edu (alternate cbat en iau.org)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network

SUPERNOVAE 2012im AND 2013ek IN NGC 6984
     S. Howerton, Arkansas City, KS, U.S.A.; A. J. Drake, S. G. Djorgovski, A.
Mahabal, M. J. Graham, and R. Williams, California Institute of Technology;
J. L. Prieto, Princeton University; M. Catelan, Pontificia Universidad
Catolica de Chile; R. H. McNaught, Australian National University; and E. C.
Beshore, S. M. Larson, and E. Christensen, Lunar and Planetary Laboratory,
University of Arizona, report the Catalina Real-time Transient Survey
discovery of an apparent supernova in public images from the Siding Spring
Survey (SSS).

 SN       2012 UT        R.A. (2000.0) Decl.      Mag.      Offset
 2012im   July 25.54   20 57 53.92  -51 52 24.8   18.9    0".6 W, 9".8 S

The variable was designated PSN J20575392-5152248 when it was posted at the
Central Bureau's TOCP webpage and is here designated SN 2012im based on the
spectroscopic confirmation reported below.  Addtional CCD magnitudes for
2012im:  2012 May 25.76 UT, [20.0 (SSS); July 27.491, 17.3 (Joseph Brimacombe,
Cairns, Australia; 43-cm CDK Planewave telescope + infrared filter; bandpass >
700 nm; position end figures 53s.88, 24".5; image posted at website URL
http://www.flickr.com/photos/43846774@N02/7660396306/); 29.463, 17.3
(Brimacombe; position end figures 53s.87, 24".5; image posted at website URL
http://www.flickr.com/photos/43846774@N02/7693912868/); 30.538, 17.6
(Brimacombe; position end figures 53s.96, 24".4; image posted at website URL
http://www.flickr.com/photos/43846774@N02/7709041256/); 31.614, R = 16.9 (P.
Miller, P. Roche, A. Tripp, R. Miles, R. Holmes, S. Foglia, and L. Buzzi;
2.0-m f/10 "Faulkes Telescope South" at Siding Spring; Bessell R filter; 120-s
image taken in good seeing and bright moonlight; position end figures 53s.93,
24".7; image posted at http://www.astrogeo.va.it/pub/TOCP/PSN_N6984_FTS.jpg);
Aug. 2.552, 17.7 (Brimacombe; position end figures 53s.87, 25".0; image posted
at URL http://www.flickr.com/photos/43846774@N02/7851648270/); Sept. 3.58,
19.9 (SSS); Oct. 20.42, 20.5 (SSS).  F. Cellier-Holzem et al. reported (at
website URL http://www.astronomerstelegram.org/?read=4300) that 2012im was a
type-Ic supernova around peak brightness from spectroscopy obtained on 2012
Aug. 8 with the New Technology Telescope at the European Southern Observatory.

     Stuart Parker, Canterbury, New Zealand, reports the discovery of an
apparent supernova (red mag 16.9) on a 30-s unfiltered CCD image (limiting mag
18.5) taken by himself on July 24.457 UT with a 30-cm Astro-Tech AT12RC
Ritchey-Chretien astrograph (+ ST10 camera) at his Parkdale Observatory in the
course of the Backyard Observatory Supernova Search.  The new object is
located at R.A. = 20h57m53s.90, Decl. = -51d52'24".5 (equinox 2000.0;
reference stars from USNO-B and UCAC3 catalogues), which is 1" west and 10"
south of the nucleus of the galaxy NGC 6984; Parker noted the closeness of
this variable to the position of SN 2012im (see above).  Nothing is visible at
this position on Digitized Sky Survey red and infrared images (limiting red
magnitude > 19) or on previous images taken by Parker with the discovery
telescope on July 13.552 (limiting red magnitude > 19).  Parker's image of
2013ek is posted at website URL http://tinyurl.com/mmkczzx.  The variable was
designated PSN J20575390-5152245 when it was posted at the Central Bureau's
TOCP webpage and is here designated SN 2013ek based on the spectroscopic
confirmation reported below.

     D. Milisavljevic, Harvard-Smithsonian Center for Astrophysics (CfA); R.
Fesen, Dartmouth College; T. Pickering and P. Kotze, South African
Astronomical Observatory and the Southern African Large Telescope; and M.
Drout, R. Margutti, and A. Soderberg, CfA, report that low-dispersion spectra
(range 320-900 nm) of PSN J20575390-5152245 = SN 2013ek, obtained on July 25.1
UT with the 10-m SALT telescope (+ RSS), show it to be a young type-Ib/c
supernova.  Cross-correlation with a library of supernova spectra using the
"Supernova Identification" code (Blondin and Tonry 2007, Ap.J. 666, 1024)
produces matches with type-Ib events around maximum light.  Notably, however,
the spectrum of 2013ek also bears close similarity to a class of rapidly
evolving type-Ic objects such as 2005ek and 2010X within a week of maximum
light (see Drout et al. 2013, posted at http://lanl.arxiv.org/abs/1306.2337).
Milisavljevic et al. find that 2012im, which was classified as a type-Ic
supernova similar to SN 1997dq around maximum by Cellier-Holzem et al.
(posted at website URL http://www.astronomerstelegram.org/?read=4300), is
also similar to this class of fast transients but at a later stage of
evolution -- i.e., a few weeks after maximum light.  Both spectra are
consistent with the redshift z = 0.016 of the host galaxy, NGC 6984.
Possible interpretations of the two events (2012im and 2013ek) include two
nearby explosions or non-terminal explosion of the same object.  Additional
observations are encouraged to confirm the spatial coincidence of the two
events and to monitor the potentially rapid evolution of this latest event.

NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
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                         (C) Copyright 2013 CBAT
2013 July 28                     (CBET 3607)              Daniel W. E. Green