[IAUC] CBET 1837: 20090609 : SUPERNOVAE 2009fx AND 2009fy

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                                                  Electronic Telegram No. 1837
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVAE 2009fx AND 2009fy
     J. Vinko, University of Texas; F. Yuan, University of Michigan; H. Marion,
University of Texas and Texas A&M University; R. Quimby, California Institute
of Technology; D. Chamarro, M. D. Sisson, and C. Akerlof, University of
Michigan; and J. C. Wheeler and E. Chatzopoulos, University of Texas, on
behalf of the ROTSE collaboration, report the discovery of two 1991T-like
type-Ia supernovae.
     SN 2009fx, which was discovered in unfiltered CCD images taken on May
29.34 (at mag about 18.5) and June 1.32 UT (mag about 18.0) with the 0.45-m
ROTSE-IIIb telescope at McDonald Observatory, is located at R.A. =
16h53m11s.28, Decl. = +23o57'54".9 (equinox 2000.0; uncertainty about 0".5),
which is 0".4 north of the center of its apparent host galaxy, SDSS
J165311.27+235754.4; according to the NASA/IPAC Extragalactic Database (NED),
the apparent host galaxy has a spectroscopic redshift of z = 0.04766.  A
finding chart has been posted at the following website URL:
http://www.rotse.net/rsvp/j165311.3+235755/j165311.3+235755.jpg.  A spectrum
(range 420-1020 nm), obtained on June 6.40 with the 9.2-m Hobby-Eberly
Telescope (HET; + Marcario Low-Resolution Spectrograph) by S. Rostopchin,
shows 2009fx to be a type-Ia supernova.  The spectrum contains the Si II
635.5-nm line and also other S II/Mg II/Fe II features that are
characteristic of type-Ia supernovae.  SNID software (Blondin and Tonry 2007,
Ap.J. 666, 1024) indicates that the spectrum best matches the spectra of
normal type-Ia supernovae between -6 and +2 days relative to maximum, at a
redshift consistent with that of the presumed host; this age estimate is
supported by the ROTSE-III lightcurve, which shows that 2009fx brightened
before the spectroscopic observation and stayed roughly constant (at mag
about 17.5) between June 5.3 and 8.3.  However, the Si II 635.5-nm feature
is weak compared to the majority of type-Ia supernovae, and the Si II
580.0-nm feature is not detected.  The spectrum is noisy at longer
wavelengths, but there is no evidence for the O I 770-nm feature, and the
Ca II infrared triplet is weak or absent.  This suggests that 2009fx belongs
to the subclass of 1991T-like, shallow-silicon supernovae (Filippenko xxxx,
Ann. Rev. A. Ap. 35, 309; Branch et al. 2006, PASP 118, 560), and it is
slightly before or at maximum light.  The expansion velocity, derived
from the minimum of the Si II 635.5-nm line, and correcting for the
host-galaxy redshift, is about 10000 km/s.
     SN 2009fy was discovered in unfiltered CCD images taken on June 1.04
with the 0.45-m ROTSE-IIId telescope at the TUBITAK National Observatory
at Bakirlitepe, Turkey, and it was also observed by ROTSE-IIIb since May
24.43, although the transient-search pipeline software did not identify it
due to a nearby saturated object.  SN 2009fy is located at R.A. =
23h24m05s.13, Decl. = +16o39'50".9 (equinox 2000.0, uncertainty about 0".5),
which is 1".4 west and 7".7 north of the center of its apparent host galaxy,
SDSS J232405.23+163943.1 (= 2MASXI J2324052+163943; z = 0.0408, according to
NED).  ROTSE-III photometry shows 2009fy at mag about 16.0 between May 24 and
28, and it decayed afterward.  A finding chart has been posted at website URL
http://www.rotse.net/rsvp/j232405.1+163951/j232405.1+163951.jpg.  An HET/LRS
spectrum obtained by S. C. Odewahn on June 8.44 shows 2009fy to be a type-Ia
supernova about two weeks after maximum.  According to SNID, the spectrum
best resembles those of SN 1991T (16 days after maximum) and SN 1997br (+12
days).  The Si II 635.5-nm line appears to be slightly blended with Na I D.
There is no O I feature at 770 nm, and the Ca triplet is weak.  The redshift
measured by SNID is z = 0.042, which is consistent with the redshift of the
host.  The photospheric velocity, estimated from the minimum of the Si II
635.5-nm feature, and corrected for the host-galaxy redshift, is about 8700
km/s.


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                         (C) Copyright 2009 CBAT
2009 June 9                      (CBET 1837)              Daniel W. E. Green