Electronic Telegram No. 1213
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT@CFA.HARVARD.EDU (science)
URL http://www.cfa.harvard.edu/iau/cbat.html


SUPERNOVA 2007sr IN NGC 4038
     G. Pojmanski, Warsaw University Observatory; and J. L. Prieto, K. Z.
Stanek, and J. F. Beacom, Ohio State University, report the detection of
SN 2007sr in several V-band images obtained by the "All-Sky Automated Survey
(ASAS) for Nearby Supernovae" before the announced discovery date (2007 Dec.
18.53 UT; cf. CBET 1172).  The supernova is absent in ASAS images obtained on
Dec. 1.36 (limiting mag 14.0) but is clearly detected in images obtained
after Dec. 7.35.  The measured V-band magnitudes (+/- 0.1 mag) are as follows:
2007 Dec. 7.35, 13.46; 14.36, 12.70; 18.35, 12.83; 22.34, 12.91; 26.33, 13.08;
2008 Jan. 3.32, 13.58; 7.35, 13.62; 11.37, 13.87; 15.31, 13.84.  ASAS data
show that this nearby type-Ia supernova (CBET 1173, 1174) had peaked around
Dec. 14 UT and was therefore detected about 7 days before peak.  A formal fit
to the ASAS V-band light curve, using the template-fitting method of Prieto
et al. (2006, Ap.J. 647, 501), gives the time of maximum as Dec. 16 at V =
12.79, with a light-curve decline rate after 15 days (delta_m15) of 0.8-0.9
mag.  Using the calibrated peak absolute magnitudes for a type-Ia supernovae
in the Hubble flow with similar decline rates from Prieto et al. (using
H_0 = 72 km/s/Mpc), a distance modulus to NGC 4038 of 32.0 mag (25 Mpc) is
estimated, after correcting for Galactic extinction in the line-of-sight
(A_V = 0.15 mag; Schlegel et al. 1998, Ap.J. 500, 525).


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                         (C) Copyright 2008 CBAT
2008 January 18                  (CBET 1213)              Daniel W. E. Green