Circular No. 6584
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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GRB 970228
     P. J. Groot and T. J. Galama, University of Amsterdam (UoA);
J. van Paradijs, UoA and University of Alabama, Huntsville; R.
Strom, Netherlands Foundation for Research in Astronomy and UoA; J.
Telting and R. G. M. Rutten, Isaac Newton Group of Telescopes, La
Palma; M. Pettini and N. Tanvir, Institute of Astronomy, Cambridge;
R. Naber, University of Groningen; C. Kouveliotou, Universities
Space Research Association; J. in 't Zand and J. Heise, Space
Research Organization of the Netherlands, Utrecht; E. Costa, M.
Feroci, and L. Piro, Instituto di Astrofisica Spaziale, CNR; F.
Frontera and G. Zavattini, Universita di Ferrara; and L. Nicastro
and E. Palazzi, Instituto Tecnologia e Studie Radiazione
Extraterrestri, CNR, report:  "Comparison of the V- and I-band
images of the error box of GRB 970228 (IAUC 6572), taken on Mar.
1.0 UT (IAUC 6574) and on Mar. 8.9 with the William Herschel
Telescope (I band, 900 s) and the Isaac Newton Telescope (V band,
2500 s), reveals one object with a large brightness variation in
both bands.  The variable had V = 21.3 and I = 20.6 on Mar. 1.0 and
V > 23.6 and I > 22.2 on Mar. 8.9.  Its position is R.A. =
5h01m46s.70, Decl. = +11o46'53".0 (equinox 2000.0; estimated
accuracy 1").  Approximately 4" away (at position end figures
46s.73, 53".0), we find another object, with V = 23.1 and I = 20.5
on Mar. 8.9, whose brightness on Mar. 1.0 (measured somewhat less
accurately because of the nearby variable) differed by < 0.2 mag
from these values.  The point-spread function of the variable, and
that of the nearby constant object, is consistent with those of
stars in the images; the two objects are therefore extended by less
than about 1".5.  Radio observations at 5 GHz obtained with the
Westerbork Synthesis Radio Telescope on Mar. 1.75 and 2.75 (12 hr
each) show no radio source at the position of the variable above
0.35 mJy (3 sigma).  The variable is located within the
intersection of the BeppoSAX WFC error box (IAUC 6572), the
BeppoSAX LECS error box (IAUC 6576), and the Ulysses/BeppoSAX
annulus (IAUC 6578); it is more than 1' away from the radio source
reported on IAUC 6576.  Its position and rapid decline
contemporaneous with that of the BeppoSAX LECS x-ray transient
(IAUC 6576) indicate that the two are related.  If the x-ray
transient is related to GRB 970228, we have detected the first
transient optical signal related to a gamma-ray burst."
     Corrigendum.  On IAUC 6582, Bloom et al., line 6, for  We
find V = 21.4,  read  We find V = 22.4,

                      (C) Copyright 1997 CBAT
1997 March 12                  (6584)            Daniel W. E. Green