Central Bureau for Astronomical Telegrams
IAUC 5914: 1993J; N Cas 1993
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Circular No. 5914
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
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MARSDEN@CFA or GREEN@CFA (.SPAN, .BITNET or .HARVARD.EDU)
SUPERNOVA 1993J IN NGC 3031
N. Bartel and M. Bietenholz, York University; M. Rupen, J.
Conway, T. Beasley, R. Sramek, and J. Romney, National Radio
Astronomy Observatory; M. Titus, Haystack Observatory; D. Graham,
Max-Planck-Institut fur Radioastronomie; V. Altunin and D. Jones,
Jet Propulsion Laboratory; A. Rius, Instituto de Astronomia y
Geodesia, Madrid; T. Venturi and G. Umana, Instituto di Radioastronomia,
CNR; R. Francis, M. McCall, M. Richer, and C. Stevenson, York
University; K. Weiler, Naval Research Laboratory; S. Van Dyk, Naval
Research Laboratory and University of California at Berkeley; N.
Panagia, Space Telescope Science Institute; W. Cannon, Institute
for Space and Terrestial Science and York University; J. Popelar,
Energy, Mines, and Resources, Ottawa; and R. Davis, Nuffield Radio
Astronomy Laboratories, report: ''Global VLBI observations of SN
1993J during the first three months after the explosion, with 9 to
15 antennas for up to 18 hours, show a supernova consistent with
being circularly symmetric and expanding uniformly. A selected set
of 30 percent of the data is now correlated and analyzed. Following
are epochs, observing frequencies, and the radii of circular
uniform disk models used in fits to the visibility data: Apr. 27.2
UT, 22.2 GHz, 96 +/- 8 microarcsec; May 17.2, 22.2, 145 +/- 14; May
17.2, 8.4, 151 +/- 11; June 27.0, 14.9, 241 +/- 21; June 27.0, 8.4,
275 +/- 9; June 27.0, 4.9, 205 +/- 85. A weighted least-squares
linear fit gives a zero-point of expansion of Mar. 25 +/- 4. With
the more precise optically derived shock-breakout date of Mar. 28.0
+/- 0.1 (Wheeler et al. 1993, Ap.J. 417, L71), the expansion rate
is 2.98 +/- 0.08 microarcsec per day. An equivalent power-law fit
gives an index of 0.96 +/- 0.07, showing no evidence yet for
deceleration of the shock front. Combining the angular expansion rate
trigonometrically with the optically derived maximum expansion
speed of the hydrogen gas, we obtain a value for the distance to
M81 of 4.0 +/- 0.6 Mpc. All errors are 1-sigma uncertainties, with
statistical and systematic contributions included. We have continued
the observations at intervals of six weeks and should be able
to obtain a sequence of detailed images of the expanding supernova."
NOVA CASSIOPEIAE 1993
Further CCD photometry by H. Mikuz, Ljubljana, Slovenia (cf.
IAUC 5912): Dec. 28.72 UT, V = 7.00 +/- 0.02, B-V = +0.68 +/- 0.04.
1993 December 30 (5914) Daniel W. E. Green
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