Circular No. 6903
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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SUPERNOVA 1998bw IN ESO 184-G82
     S. R. Kulkarni and J. S. Bloom, California Institute of
Technology; D. A. Frail, National Radio Astronomy Observatory; and
R. Ekers, M. Wieringa, R. Wark, and J. L. Higdon, Australian
Telescope National Facility, report:  "Within the localization of
GRB 980425 (IAUC 6884), Galama et al. (IAUC 6895) reported a
possible supernova candidate for which Wieringa et al. (IAUC 6896)
saw a brightening radio source.  The object appears to be a young
supernova, possibly of type-Ib (IAUC 6901), which exploded on or
around Apr. 24, the epoch of GRB 980425.  For an assumed expansion
speed of 20 000 km/s and a distance of 44 Mpc to the host galaxy of
the supernova (from the redshift given on IAUC 6896), we derive a
brightness temperature of 3 x 10E14 K from the observed 39 mJy at 6
cm on May 5 (IAUC 6896).  This is in excess of the usual Compton
limit of 10E12 K.  Despite this, no x-ray emission is seen (GCN 69).
Thus we are forced to invoke a relativistic expansion speed that
results in a larger source size and correspondingly smaller
brightness temperature.  We suggest that the radio emission arises
in a relativistic shock and the optical emission in a standard
low-velocity shock.  We urge observers to carry out higher-
frequency radio observations and infrared observations, as the
radio spectrum may rapidly evolve.  The model predicts that the
radio source should not exhibit diffractive scintillation.  VLBI
observations would be of great value."
     Visual magnitude estimates by B. Monard, Pretoria, South
Africa:  May 10.14 UT, 13.5; 13.15, 13.5.


SUPERNOVA 1988ae IN MCG +02-53-002
     J. Mueller reports her discovery of an apparent supernova (mag
about 16.5) on a plate taken with the 1.2-m Oschin Schmidt
Telescope on 1988 Sept. 15 in the course of the second Palomar Sky
Survey.  SN 1988ae is located at R.A. = 20h44m09s.0, Decl. =
+12o24'53" (equinox 2000.0), which is 10" west and 15" south of the
center of MCG +02-53-002.  The star also appears on a Sky Survey
plate taken by Mueller on 1988 Aug. 12 at mag about 17.  Sky Survey
plates taken on 1988 Aug. 6 and 1990 Aug. 18 do not show SN 1988ae,
neither does the object appear on the Digital Sky Survey.

                      (C) Copyright 1998 CBAT
1998 May 13                    (6903)            Daniel W. E. Green