[IAUC] CBET 1059: 20070911 : SUPERNOVA 2007if

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                                                  Electronic Telegram No. 1059
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVA 2007if
     On August 28, F. Yuan, Physics Department, University of Michigan;
and R. Quimby, University of Texas, on behalf of the ROTSE collaboration,
reported the discovery of a variable object (mag 19.5 +/- 0.1) in Pisces
on unfiltered CCD images taken on Aug. 16.29 UT with the 0.45-m ROTSE-IIIb
telescope at McDonald Observatory.  The new object, which was quickly
posted on the Central Bureau's unconfirmed-objects webpage, is located at
1h10m51s.37, Decl. = +15o27'39".9 (equinox 2000.0; uncertainty < 1").
There were then 13 images showing the variable taken by the ROTSE-IIIb and
by the ROTSE-IIIc telescopes at the H.E.S.S. site at Mt. Gamsberg, Namibia.
Additional magnitudes (calibrated relative to R magnitudes from the
USNO-B1.0 catalogue) for the variable:  Aug. 14.30, [20.1; 19.28, 18.3;
22.01, 17.8; 24.26, 17.8; 26.38, 17.2; 26.98, 17.6.  The field has been
monitored by ROTSE-III telescopes on a daily basis before and after
the discovery, weather permitting; the variable recently has remained
around mag 17, up to Sept. 9.98 (when observed at the H.E.S.S. site).  No
object (including a possible host galaxy) is seen at this position in the
Sloan Digital Sky Survey images, a Digitized Sky Survey image, or any USNO
archive plates.  A spectrum was taken with the MDM 2.4-m telescope by C.
Peters and J. Thorstensen (Dartmouth College) around Aug 22.4 UT; the low
S/N data may show a broad absorption feature around 575 nm.  There might
also be a P-Cyg feature at about 699 nm, which could be H-alpha at z =
0.066.  However, none of these features are significant in the preliminary
analysis, and thus no evidence can be claimed for determining the nature
of the transient.  Spectroscopy at the HET telescope on Aug. 29 also
failed to show significant features that could identify the nature of the
transient.  Further information on the ROTSE observations including a
finding chart and a light curve can be found at:
http://www.rotse.net/transients/j0110+1527/index.html.
     Today, Yuan and Quimby, joined by C. Akerlof and J. Miller, University
of Michigan; C. Peters and J. Thorstensen, Dartmouth College; by the "Nearby
Supernova Factory" collaboration (C. Baltay, A. Bauer, D. Rabinowitz, and R.
Scalzo, Yale University; G. Rigaudier and E. Pecontal, Centre de Recherche
Astronomique de Lyon; C. Buton, Y. Copin, E. Gangler, G. Smadja, and C. Tao,
Institut de Physique Nucleaire de Lyon; P. Antilogus, S. Bailey, R. Pain, R.
Pereira, and C. Wu, Laboratoire de Physique Nucleaire et de Haute Energies
de Paris; G. Aldering, C. Aragon, S. Bongard, M. Childress, S. Loken, P.
Nugent, S. Perlmutter, K. Runge, R. C. Thomas, and B. A. Weaver, Lawrence
Berkeley National Laboratory; D. Birchall, Institute for Astronomy,
University of Hawaii, Hilo; and J. Cough, J. Holtzman, New Mexico State
University, Las Cruces); and by A. Rau and M. Kasliwal, California Institute
of Technology; and A. Gal-Yam, Weizman Institute of Science, Rehovot, Israel,
report that the variable is spectroscopically similar to the possibly
"super-Chandrasekhar-mass" type-Ia supernova 2003fg (cf. IAUC 8147, 8148;
Howell et al. 2006, Nature 443, 308), and thus the new variable is hereby
designated as SN 2007if.  The "Nearby Supernova Factory" collaboration has
independently discovered 2007if at mag 18.4 in images obtained on Aug. 25.4
UT using the QUEST-II camera on the Palomar Oschin 1.2-m Schmidt telescope,
operated by the Palomar-QUEST Consortium.  By Sept. 3, 2007if had brightened
to mag 17.7 (both magnitudes calibrated to the R band, via comparison with
the USNO-B1.0 catalogue); nothing was detected at this position in Palomar
images obtained on Aug. 9.5 (no limiting magnitude provided).
     A spectrum (range 320-1000 nm) of 2007if, obtained on Aug. 26.5 with
the SuperNova Integral Field Spectrograph (SNIFS) on the University of
Hawaii 2.2-m telescope, consists of a blue continuum with scattered small-
amplitude absorption features superimposed.  Lacking additional constraints
(such as host-galaxy redshift), the target was not positively identified as
a type-Ia supernova.  Additional spectroscopy of 2007if was obtained by
Kasliwal, Rau, and Gal-Yam using the Double Spectrograph mounted on the
Hale 5-m telescope at Palomar on Sept. 6.45; inspection of a quick reduction
of this spectrum suggested that 2007if is a type-Ia supernova, and further
analysis using the 'Superfit' supernova-spectral-identification code (Howell
et al. 2005, Ap.J. 634, 1190) shows that the best matches are obtained with
type-Ia supernovae well before peak, indicating that 2007if must have been
detected shortly after explosion.  An additional SNIFS spectrum of 2007if,
obtained on Sept. 10.5, is an unambiguous match to that of SN 2003fg.  A
comparison plot (corrected to rest-frame, assuming z = 0.07 for this object)
is available at http://snfactory.lbl.gov/snf/data/SNF20070825-001.png.  The
C II identification around 400 nm reported by Howell et al. can also be made
for 2007if:  after a small correction for the B-band telluric absorption,
C II 658-nm is clearly visible, as predicted by Howell et al.  Assuming z =
0.07 and the magnitudes reported above (as bright as mag 17), it is noted
that 2007if is clearly overluminous (absolute magnitude M < -20) for a
type-Ia supernova, agreeing well with the spectroscopic results and
suggesting a "super-Chandrasekhar-mass" event.


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                         (C) Copyright 2007 CBAT
2007 September 11                (CBET 1059)              Daniel W. E. Green