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IAUC 8413: 2004et

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                                                  Circular No. 8413
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVA 2004et IN NGC 6946
     T. Zwitter, University of Ljubljana; and U. Munari,
Astronomical Observatory, Padova, report the discovery by S.
Moretti, on unfiltered CCD images taken on Sept. 27 with a 0.4-m
telescope at Ravenna, of a bright supernova (mag 12.8) in NGC 6946.
The new object is located at R.A. = 20h35m25s.33, Decl. =
+60o07'17".7 (equinox 2000.0).  A high-resolution spectrogram,
secured on Sept. 28 with the echelle spectrograph at the 1.82-m
telescope in Asiago, shows a relatively featureless spectrum with a
very broad, low-contrast H_alpha emission.  Sharp interstellar Na I
absorption lines are observed at heliocentric radial velocities of
-21.1 (+/- 0.7) and +45.2 (+/- 0.4) km/s, matching expectation for
separate origin within our galaxy and NGC 6946.  The equivalent
width of Na I D_2 lines corresponds to a total reddening of E(B-V)
= 0.41 mag, following the calibration by Munari and Zwitter (1997,
A.Ap. 318, 269).
     H. Yamaoka, Kyushu University, reports that K. Itagaki (Teppo-
cho, Yamagata, Japan) found nothing at the location of SN 2004et on
an unfiltered CCD image taken on Sept. 19.655 UT with a 0.60-m
reflector (limiting mag 18.5).  A. Klotz, C. Pollas and M. Boer,
Observatoire de Haute Provence, report R magnitudes for 2004et,
obtained with the robotic TAROT telescope:  Sept. 19.989, [19.2 +/-
0.45; 21.021, [17.6 +/- 1.3; 22.017, [19.4 +/- 1.2; 22.983, 15.17
+/- 0.16; 25.978, 12.7 +/- 0.3; 27.035, 12.8 +/- 0.4; 27.974, 12.2
+/- 0.1; 28.092, 12.6 +/- 0.5.
     W. Li and A. V. Filippenko, University of California, Berkeley;
and S. D. Van Dyk, Infrared Processing and Analysis Center,
California Institute of Technology, report that SN 2004et was
imaged on Sept. 30 UT with the 0.76-m Katzman Automatic Imaging
Telescope (KAIT) at Lick Observatory, yielding position end figures
25s.37, 17".8 (equinox 2000.0; uncertainty about 0".2 in each
coordinate).  A faint object, possibly extended, appears at this
location on multi-band images of NGC 6946 taken with the Kitt Peak
0.9-m telescope on 1989 May 30.  Based on calibrations of the field
on three photometric nights with the Lick Nickel 1-m telescope,
they measure the object at R = 20.8 +/- 0.2, adding that it was not
detected in the Kitt Peak B- and I-band images (B > 21.3, I > 19.7).
Using a distance of 5.5 Mpc to NGC 6946 (Shapley et al. 2001, Ap.J.
Suppl. 137, 139), and E(B-V) = 0.41 mag (from Zwitter and Munari,
above), the absolute magnitudes of the object are M_B > -9.1, M_R =
-8.9, and M_I > -9.7.  The high luminosity makes it likely to be a
star cluster rather than a single star.  Unfortunately, there do
not appear to be Hubble Space Telescope or KAIT pre-explosion
images of the site of SN 2004et.

                      (C) Copyright 2004 CBAT
2004 September 30              (8413)            Daniel W. E. Green

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