Circular No. 6730
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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GRB 970828
     A. J. Castro-Tirado and J. Gorosabel, Laboratorio de
Astrofisica Espacial y Fisica Fundamental, Madrid; J. Iglesias, L.
M. Cairos, J. Vilchez, A. Mora, C. Gutierrez, J. Licandro, and V.
Bejar, Instituto de Astrofisica de Canarias (IAC), La Laguna; and
J. Greiner, Astrophysikalisches Institut, Potsdam, report:
"Following the detection of the x-ray afterglow from GRB 970828 by
RXTE (IAUC 6726, 6727), R-band images were obtained (on Aug. 29.03
and 29.95 UT) with the Teide Observatory 0.8-m IAC-80 telescope,
and unfiltered (Aug. 29.91, 30.09, and 31.10) and B-band (Aug.
30.92) images were obtained with the Calar Alto 2.2-m telescope (+
CAFOS).  About 90 objects are detected in the ASCA error box (IAUC
6729), down to mag 23.  No variations larger than 0.3 mag are seen
for objects brighter than mag 22.5.  An object of magnitude B =
22.7 +/- 0.3 is clearly seen in the 25-min B-band image but only
barely visible in the 60-min, co-added unfiltered image.  Its
position (+/- 1") is R.A. = 18h08m32s.7, Decl. = +59o18'22".9
(equinox 2000.0) -- i.e., 16" west and 13" north of a galaxy (B =
20.2) seen on the Palomar Sky Survey.  It lies in the intersection
between the RXTE and ASCA error boxes."
     D. A. Frail, National Radio Astronomy Observatory and S. R.
Kulkarni, California Institute of Technology, communicate: "The VLA
was used to observe the field of GRB 970828 (IAUC 6726) on three
occasions.  A single radio source was detected within the area
defined by the intersection of the refined RXTE ASM error ellipse
(IAUC 6728) of GRB 970828 and the ASCA error circle (IAUC 6729).
The position of the radio source is R.A. = 18h08m25s.51 +/- 0s.05,
Decl. = +59o18'08".5" +/- 0".4 (equinox 2000.0).  On Aug. 31.19 and
Sept. 1.27 UT, the source had a mean flux of 0.36 and 0.27 mJy,
respectively, at 6 and 3.6 cm; the rms error in the flux is 0.03
mJy.  There is some evidence of variability, since this radio
source was not detected at 6 cm on Aug. 28.88.  A 4-sigma upper
limit to the flux of the source at this epoch is 0.18 mJy."
     S. G. Djorgovski and S. C. Odewahn, California Institute of
Technology; and Kulkarni and Frail further report:  "CCD images of
the radio field noted by Frail and Kulkarni (above) were obtained
by C. C. Steidel, K. L. Adelberger, and M. Kellog at the prime
focus of the 5-m Hale telescope on Aug. 30, 31, and Sept. 1 UT.  We
have identified a faint object (magnitude R about 24.5 +/- 0.5)
that is coincident with this radio source.  The source did not vary
significantly over the three-night interval."

                      (C) Copyright 1997 CBAT
1997 September 1               (6730)            Daniel W. E. Green