Central Bureau for Astronomical Telegrams
IAUC 8152: 2003gd
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Circular No. 8152
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVA 2003gd IN M74
R. Kotak and W. P. S. Meikle, Imperial College, London, and
S. J. Smartt, Institute of Astronomy, Cambridge, on behalf of the
European Supernova Collaboration, report that a spectrum (range
about 400-840 nm) of SN 2003gd was obtained at the William Herschel
Telescope (+ ISIS spectrograph) by C. Benn on June 14.2 UT.
Comparison of a preliminary reduction of the spectrum with spectra
of SN 1992H and SN 1987A (Filippenko 1997, ARAA 35, 309) indicates
that the new supernova is of type II, roughly 2 months post-
explosion. The strong H_alpha P-Cyg profile extends from -8800 to
+7100 km/s in the host-galaxy rest frame.
M. Phillips, Carnegie Observatories, reports that echelle
spectroscopy of SN 2003gd, reduced by M. Navarrete from
observations obtained on June 14 UT by G. Preston with the Baade
6.5-m telescope at Las Campanas, indicates that this is a type-II
event that was discovered approximately 1 month after explosion.
Further to IAUC 8150, R. H. McNaught provides a better
position for SN 2003gd (and revised red mag 13.3 on June 13.84 UT):
R.A. = 1h36m42s.65, Decl. = +15o44'19".9 (equinox 2000.0;
uncertainties +/- 0".1 in each coordinate).
S. J. Smartt, J. R. Maund, and M. A. Hendry, Institute of
Astronomy, Cambridge, report that the position of SN 2003gd lies on
deep pre-explosion archive images from the Hubble Space Telescope
(+ WFPC2) and Gemini North (+ GMOS). Differential astrometry,
using an image obtained at the William Herschel Telescope (+ Aux
Port Camera) by C. R. Benn on June 15.2 UT, indicates the presence
of a progenitor star (V = 26.1 +/- 0.15) in the 3100-s F606W WFPC2
image at a distance of 0".06 +/- 0".2 from the supernova position.
The star has an absolute magnitude of M_V = -3.5, assuming the
distance and foreground reddening given by Smartt et al. (2002,
Ap.J. 572, L147). The apparent progenitor (I approximately 23.8,
V-I = +2.3) is detected on the GMOS i' band (0".6 seeing) but is
close to a neighboring star that is resolved in the HST F606W
image. The color and absolute magnitude suggest that this star is
a red supergiant, probably of spectral type M, with luminosity log
(L/L_sun) approximately 4 and a relatively low mass in the range
8-10 M_sun. Smartt et al. add that they will use the HST override
program to observe SN 2003gd (with ACS), so as to obtain a
significant reduction in the astrometric error, as well as to
determine the extinction in this region. Given the likelihood of a
progenitor detection, observations of this supernova at all
wavelengths are strongly encouraged.
(C) Copyright 2003 CBAT
2003 June 18 (8152) Daniel W. E. Green
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