Electronic Telegram No. 3643
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 2013fb IN IC 221 = PSN J02224207+2816012
     S. Nakano, Sumoto, Japan, reports the discovery by Masaki Tsuboi
(Kuchita-minami, Asakita-ku, Hiroshima, Japan) of an apparent supernova (mag
16.0) on two unfiltered 20-s CCD frames (limiting mag 17.8) taken on Aug.
27.683 UT using a 0.30-m f/5.3 reflector (+ ST-9XE camera).  The new object is
located at R.A. = 2h22m42s.07, Decl. = +28d16'01".2 (equinox 2000.0), which is
15".6 east and 35".9 north of the center of the galaxy IC 221.  Nothing is
visible at this position on a red Digitized Sky Survey image (limiting mag
about 21).  The discovery image has been posted at the following website URL:
http://tenku.dee.cc/PSN/IC221130828-01.jpg.  The variable was designated PSN
J02224207+2816012 when it was posted at the Central Bureau's TOCP webpage and
is here designated SN 2013fb based on the spectroscopic confirmation reported
below.  Additional CCD magnitudes for 2013fb:  Aug. 18.718, [18.2 (Tsuboi);
28.548, 15.6 (Tsuboi; limiting mag 17.3); 28.713, 16.0 (Ken-ichi Kadota, Ageo,
Saitama-ken, Japan, 0.25-m f/5 reflector + SBIG ST-9E camera; limiting mag
18.8; ten stacked 90-s frames; position end figures 42s.07, 01".1; offset 16"
east, 36" north; galaxy center at position end figures 40s.86, 15'24".9;
GSC-ACT reference stars; communicated by Nakano; image posted at website URL
http://members.jcom.home.ne.jp/kenic-k/image/PSNinIC221-20130828.jpg); 28.882,
16.3 (Gianluca Masi and Francesca Nocentini, remotely using a 43-cm telescope
at Ceccano, Italy; position end figures 42s.07, 01".0); 29.547, 16.4
(Toshihide Noguchi, Katori, Chiba-ken, Japan, 0.23-m f/6.3 reflector + BITRAN
BT-11E camera; position end figures 42s.07, 01".1; offset 15" east, 36" north;
UCAC-4 reference stars; sixteen stacked 40-s exposures; limiting mag 18.0;
image posted at URL http://park8.wakwak.com/~ngc/images/PSNinIC221.jpg;
communicated by Nakano); 29.699, 16.4 (J. Brimacombe, Cairns, Australia; 41-cm
telescope + infrared filter; bandpass > 700 nm; position end figures 42s.07,
01".0; image posted at http://www.flickr.com/photos/43846774@N02/9632344367/);
30.027, V = 15.9 (Massimiliano Martignoni, Magnago, Italy, 0.25-m f/10
Schmidt-Cassegrain reflector; position end figures 42s.08, 00".9); 30.419,
16.0 (T. Yusa, Osaki, Japan; remotely using an iTelescope 0.43-m astrograph
near Mayhill, NM, U.S.A.; position end figures 42s.09, 00".9; UCAC4 reference
stars; three stacked 120-s exposures; limiting mag 20.0; image posted at URL
http://space.geocities.jp/yusastar77/supernova/PSNinI221_130830.htm).  Masi
and Nocentini add that a spectrogram obtained on Aug. 28.966 remotely using a
36-cm robotic telescope at Ceccano using a 100 lines/mm grating (providing a
dispersion of 3.41 nm/pixel) shows a clear Si II absorption around 615 nm,
suggesting that 2013fb is a type-Ia supernova.

     K. Ayani, Bisei Astronomical Observatory (BAO), Ibara, Okayama, Japan,
obtained a low-resolution spectrogram (range 400-800 nm, resolution 0.5 nm at
H-alpha) of PSN J02224207+2816012 = SN 2013fb with the BAO 1.01-m telescope on
Aug. 28.7 UT.  The spectrum is that of a type-Ia supernova around maximum.
The absorption minimum of the Si II 635.5-nm feature is blueshifted by about
14000 km/s, assuming the resession velocity of IC 221 to be 5090 km/s (Huchra
et al. 1999, Ap.J. Suppl. 121, 287).

     K. Takaki, Y. Moritani, and K. S. Kawabata, Hiroshima University; and M.
Yamanaka, Kyoto University, obtained a low-resolution optical spectrogram
(range 450-900 nm) of PSN J02224207+2816012 = SN 2013fb on Aug. 28.70 UT with
the 1.5-m Kanata telescope (+ HOWPol) at Higashi-Hiroshima Observatory.  The
spectrum is consistent with a type-Ia supernova around or a few days before
maximum.  A comparison with a library of supernova spectra using GELATO
(Harutyunyan et al. 2008, A.Ap. 488, 383) suggests that the spectrum of 2013fb
is good match to that of SN 2007af at -2 days or SN 2002bo at -7 days.  The
velocity of the Si II 635.5-nm absorption line is about -14000 km/s.


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2013 CBAT
2013 September 1                 (CBET 3643)              Daniel W. E. Green