[IAUC] CBET 4164: 20151112 : SUPERNOVA 2015U IN NGC 2388 = PSN J07285387+3349106

[quai en eps.harvard.edu]

                                                  Electronic Telegram No. 4164
Central Bureau for Astronomical Telegrams
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SUPERNOVA 2015U IN NGC 2388 = PSN J07285387+3349106
     Further to CBET 4026, S. Kumar, H. Yuk, W. Zheng, and A. V. Filippenko,
University of California at Berkeley, report the LOSS discovery of a possible
supernova in NGC 2388 on unfiltered KAIT images:

 SN       2015 UT       R.A. (2000.0) Decl.      Mag.      Offset
 2015U    Feb. 13.222  7 28 53.87  +33 49 10.6   16.4    5".5 E, 2".2 N

A finding chart for thie variable was posted at the following website URL:
http://astro.berkeley.edu/~zwk/findingchart/PSN_J07285387+33491060.jpg.
The variable was designated PSN J07285387+3349106 when it was posted at the
Central Bureau's TOCP webpage and is here designated SN 2015U based on the
spectroscopic confirmation reported below.  Additional approximate CCD
magnitudes for 2015U:  Feb. 10.24 UT, 17.1 (KAIT); 11.26, 16.5 (KAIT);
17.811, 16.5 (G. Masi; remotely using a 43-cm telescope at Ceccano, Italy;
position end figures 53s.91, 10".1); 17.882, V = 16.3 (M. Martignoni, Magnago,
Italy; 25-cm Schmidt-Cassegrain reflector; position end figures 53s.87,
09".5).

     P. Ochner, S. Benetti, A. Pastorello, E. Cappellaro, N. Elias-Rosa, L.
Tartaglia, G. Terreran, L. Tomasella, M. Turatto, and S. Zaggia, Osservatorio
Astronomico di Padova, INAF; and F. Patat, European Southern Observatory,
report that an optical spectrogram (range 340-925 nm; resolution 1.4 nm) of
PSN J07285387+3349106 = SN 2015U, obtained on 2015 Feb. 18.79 UT with the
Asiago 182-cm Copernico Telescope (+ AFOSC) in the framework of the Asiago
Transient Classification Program (Tomasella et al. 2014, AN 335, 841), shows
an almost featureless continuum, but with a narrow, strong interstellar Na I
D absorption at the redshift of the host galaxy.  From the equivalent width
of this feature (about 0.66 nm), and following Turatto et al. 2003 (Proc.
>From Twilight to Highlight:  The Physics of Supernovae, ESO/MPA/MPE Workshop,
Garching, 2002 July 29-31), the authors estimate a reddening value E(B-V)
around 1.  After reddening correction, they infer a black-body temperature of
about 15300 K.  These characteristics are consistent with those of a very
young core-collapse supernova.  Narrow emission lines (H-alpha, [N II], and
[S II]) are spatially extended and therefore attributed to the host-galaxy
background.  However, from a closer inspection of the spectrum, unresolved
emission lines of He I (including 587.6 nm and 706.5 nm) are detected and
are attributed to the transient.  For this reason, the authors tentatively
suggest for PSN J07285387+3349106 a type-Ibn classification (Pastorello et
al. 2008, MNRAS 389, 113; Pastorello et al. 2015, MNRAS, in press, preprint
via arXiv 1502.04946).  Accounting for the bright apparent magnitude of the
transient at discovery, this yields an absolute magnitude of -20.2.  The
Asiago classification spectra are posted at URL http://sngroup.oapd.inaf.it.

     I. Shivvers, W. Zheng, and A. V. Filippenko, University of California,
Berkeley, report that inspection of a CCD spectrogram (range 350-1000 nm),
obtained on Feb. 15.256 UT with the Shane 3-m reflector (+ Kast spectrograph)
at Lick Observatory, shows that PSN J07285387+3349106 = 2015U is a young and
heavily-reddened type-Ibn supernova.  The spectrum shows a blue continuum with
narrow (unresolved) helium emission features atop broader wings (FWHM of a few
thousand kms) -- similar to the early spectra of type-IIn supernovae, except
with weak or no hydrogen features.


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

                         (C) Copyright 2015 CBAT
2015 November 12                 (CBET 4164)              Daniel W. E. Green