Central Bureau for Astronomical Telegrams
IAUC 5762: 1993J
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Circular No. 5762
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)
TWX 710-320-6842 ASTROGRAM CAM EASYLINK 62794505
MARSDEN@CFA or GREEN@CFA (.SPAN, .BITNET or .HARVARD.EDU)
SUPERNOVA 1993J IN NGC 3031
R. G. Strom, Netherlands Foundation for Research in Astronomy
(NFRA), Dwingeloo, reports on behalf of the NFRA supernova team (A.
J. Boonstra, R. Braun, A. G. de Bruyn, A. R. Foley, and himself):
"We have made recent 6-cm observations of SN 1993J with the Westerbork
Telescope. On Apr. 8.60-9.10 UT, no object brighter than 0.4
+/- 0.2 mJy is seen within 10" of SN 1993J. In an observation on
Apr. 12.59-13.09, we have possibly detected a source within 1" of
the VLA position (IAUC 5759). Its flux density at 6 cm (4869 MHz)
was 0.44 +/- 0.16 mJy. This is consistent with detections made at
shorter wavelengths (IAUC 5751, 5752, 5759), and also with the
temporal development of the source spectrum. The flux density of
the nuclear component in NGC 3031 is 123 mJy in both measurements."
N. Panagia, Space Telescope Science Institute and University
of Catania; and S. D. Van Dyk and K. W. Weiler, Naval Research
Laboratory, write: "The available radio observations of SN 1993J are
already sufficient for initial modelling of the progenitor star and
projection of the likely evolution of the radio emission. Applying
the Chevalier mini-shell model, which has been shown appropriate
for other radio supernovae (Weiler et al. 1986, Ap.J. 301, 790)
with the usual assumptions for the stellar wind from the red
supergiant progenitor star, and assigning a normal spectral index of
-0.7 and an index for the emission decay rate of -0.7, the model
yields a pre-supernova mass loss rate of about 2 x 10E-6 M(sun)/yr.
The stellar evolution models of Maeder and Meynet (1988, A.Ap.
Suppl. 76, 411) then imply a ZAMS mass for the progenitor of SN
1993J of < 15 M(sun). Comparison with other known radio supernovae,
however, indicates that SN 1993J is quite similar in radio properties
to SN 1980K and SN 1981K and may represent the lower end of
the mass range of stars that can explode as type-II supernovae.
This relative consistency of properties may indicate a relatively
firm lower limit to the radio properties of type-II supernovae, and
therefore a possible minimum distance indicator. Our modelling also
results in predictions of the radio flux density to be expected
from SN 1993J at various frequencies to assist planning observations
at other telescopes. Taking Mar. 26 as day 1, the expected peak
flux densities at different radio frequencies are as follows: Apr.
14 (day 20), about 20 mJy at 23 GHz; Apr. 19, about 20 mJy at 15
GHz; May 4, about 25 mJy at 8.4 GHz; May 19, about 30 mJy at 5 GHz;
Aug. 2 (day 130), about 35 mJy at 1.4 GHz. After peak, the flux
density at each frequency should decline approximately as tE-0.7."
1993 April 16 (5762) Daniel W. E. Green
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