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IAUC 6576: GRB 970228

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                                                 Circular No. 6576
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
     E. Costa, M. Feroci, L. Piro, and M. N. Cinti, Istituto di
Astrofisica Spaziale (IAS), CNR, Frascati; F. Frontera and G.
Zavattini, Universita di Ferrara; L. Nicastro, E. Palazzi, D. Dal
Fiume, and M. Orlandini, Istituto Tecnologie e Studio Radiazioni
Extraterrestri (ITESRE), CNR, Bologna; J. in 't Zand, J. Heise, and
R. Jager, Space Research Organization of the Netherlands (SRON),
Utrecht; A. Parmar and A. Owens, Space Science Department, ESTEC;
S. Molendi, Istituto di Fisica Cosmica e Tecnologie Relative, CNR,
Milano; G. Cusumano, M. C. Maccarone, and S. Giarrusso, Istituto di
Fisica Cosmica e Applicazioni Informatica, CNR, Palermo; L. A.
Antonelli, F. Fiore, P. Giommi, J. M. Muller, L. Salotti, G.
Gennaro, M. Stornelli, G. Crisigiovanni, R. Ricci, and A. Coletta,
BeppoSAX, Rome; and R. C. Butler, Agenzia Spaziale Italiana, Rome,
report:  "The BeppoSAX GRBM/WFC error box of GRB 970228 (IAUC 6572)
was observed with the BeppoSAX Narrow Field Instruments on Feb.
28.458 UT for 15~000 s (8 hr after the gamma-ray burst).  A
previously unknown intense x-ray source, SAX J0501.7+1146, has been
detected by the MECS and LECS at the same position (R.A. = 5h01m44s,
Decl. = +11o46'.7, equinox 2000.0; estimated error radius 50").
This position lies at the edge of the reported BeppoSAX WFC error
box (IAUC 6572).  The source flux is (2.8 +/- 0.4) x 10E-12 erg
cmE-2 sE-1 in the MECS (2-10 keV) and (4.0 +/- 0.6) x 10E-12 erg
cmE-2 sE-1 in the LECS (0.5-10 keV).  The field was observed again
on Mar. 3.734, and a source was detected at a position consistent
with the previous one, but at a flux level lower by a factor of 20.
Given this very peculiar time variability, we conclude that the new
BeppoSAX x-ray source is related to GRB 970228."
     D. A. Frail, National Radio Astronomy Observatory; S. R.
Kulkarni, California Institute of Technology; E. Costa, M. Feroci,
and L. Piro, IAS, Frascati; L. Nicastro, D. Dal Fiume, and E.
Palazzi, ITESRE, Bologna; F. Frontera, Universita di Ferrara; and R.
Jager and J. Heise, SRON, report:  "Observations at 20 cm with the
Very Large Array on Mar. 1.03 and 2.16 UT, and at 6 cm on Mar. 4.04,
centered on the gamma-ray burst position given on IAUC 6572, have
detected a single, unresolved radio source in the error circle of
the x-ray transient seen by Costa et al. (above).  The radio source
is at R.A. = 5h01m41s.68 +/- 0s.01, Decl. = +11o47'05".1 +/- 0".2
(equinox J2000.0).  Flux densities measured on these three days are
0.80, 0.76, and 0.62 mJy, respectively, with errors of order 0.15
mJy."

                      (C) Copyright 1997 CBAT
1997 March 6                   (6576)            Daniel W. E. Green

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