[IAUC] CBET 2777: 20110803 : SUPERNOVA 2011ei IN NGC 6925 = PSN J20342262-3158236

Mie Sep 14 16:18:44 ART 2011

                                                  Electronic Telegram No. 2777
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


SUPERNOVA 2011ei IN NGC 6925 = PSN J20342262-3158236
     Peter Marples, Loganholme Observatory, Queensland, Australia, reports the
discovery by Stuart Parker (Oxford, Canterbury, New Zealand) of an apparent
supernova (red mag 18.0) on a 30-s unfiltered CCD image taken on July 25.434
UT with a Celestron C14 35-cm f/6.3 Schmidt-Cassegrain reflector (+ ST10 CCD
camera).  Colin Drescher (Calamvale, Queensland, Australia) measured the
magnitude and the position of the new object to be R.A. = 20h34m22s.62, Decl.
= -31d58'23".6 (equinox 2000.0), which is 26" east and 28" north of the
nucleus of the galaxy NGC 6925.  Nothing is visible at this position on a red
Digitized Sky Survey image from 1990 Sept. 24 (no limiting magnitude provided).
The variable was designated as PSN J20342262-3158236 when posted at the
Central Bureau's TOCP webpage and is here designated SN 2011ei based on the
spectroscopic reports below.  Additional magnitudes for 2011ei:  2011 June
23.58, [19.1 (Parker; red magnitude); July 26.43, 18.3 (Greg Bock, Leyburn,
Queensland, Australia; Meade 35-cm LX200 ACF Schmidt-Cassegrain telescope
+ ST10 CCD camera; unfiltered red mag measured by Marples; limiting red
mag 18.6); 27.322, 18.7 (Joseph Brimacombe, Cairns, Australia; remotely using
a 51-cm RCOS telescope + unfiltered STL11K camera at the New Mexico Skies
observatory near Mayhill, NM, U.S.A.; position end figures 22s.63, 22".9
image posted at URL http://www.flickr.com/photos/43846774@N02/5982678302/);
27.508, 17.8 (Brimacombe, Coral Towers Observatory, Cairns; 30-cm telescope
+ red filter; position end figures 22s.52, 24".1; 27.515, 17.7 (Brimacombe;
40-cm RCOS telescope + STL6K camera + infrared filter; position end figures
22s.60, 22".4; http://www.flickr.com/photos/43846774@N02/5983785346/); Aug.
2.330, 16.9 (Brimacombe; red filter; image posted at website URL
http://www.flickr.com/photos/43846774@N02/6002976621/).

     M. Stritzinger, Stockholm University; N. Morrell, Las Campanas
Observatory; and G. Pignata, Universidad Andres Bello, report that they
obtained a spectrum (range 373-945 nm) of PSN J20342262-3158236 = SN 2011ei
on July 29.2 UT with the Magellan II Clay 6.5-m telescope (+ LDSS3) at Las
Campanas Observatory.  The spectrum is consistent with a type-II supernova.
Comparison with a library of supernova spectra (Blondin and Tonry 2007, Ap.J.
666, 1024) suggests that 2011ei is most similar to the type-IIb supernovae
1993J and 1996cb prior to maximum light, although a comparison to SN 1987A
at early phases cannot be ruled out.

     D. Milisavljevic and R. Fesen, Dartmouth College; K. Nordsieck,
University of Wisconsin; and T. Pickering, A. Gulbis, and D. O'Donoghue, South
African Astronomical Observatory, on behalf of a larger SALT Commissioning
Team, report that low-dispersion spectra (range 320-900 nm), obtained July
29.8 UT with the 10-m SALT telescope (+ RSS), show PSN J20342262-3158236 =
SN 2011ei to be a type-II supernova.  Comparison with spectra retrieved from
the Supernova Spectrum Archive (SUSPECT; see the following website URL:
http://bruford.nhn.ou.edu/~suspect/index.html) shows a good match to the
energetic type-IIb 'hypernova' 2003bg at approximately 7 days before maximum
light (Hamuy et al. 2009, Ap.J. 703, 1612).  Assuming a redshift of z =
0.0093 for the host galaxy, NGC 6925 (Koribalski et al. 2004, A.J. 128, 16),
the H-alpha P-Cyg profile shows broad emission spanning 622-700 nm with a
relatively shallow absorption minimum blueshifted around -15700 km/s.


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                         (C) Copyright 2011 CBAT
2011 August 3                    (CBET 2777)              Daniel W. E. Green