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IAUC 6578: GRB 970228; C/1995 O1

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                                                 Circular No. 6578
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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GRB 970228
     S. M. Matz, Northwestern University; K. McNaron-Brown, George
Mason University; and J. E. Grove and G. H. Share, Naval Research
Laboratory, report on behalf of the OSSE team: "The OSSE instrument
on the Compton Gamma Ray Observatory had good exposure to the
position of GRB 970228 (IAUC 6572) before and after the burst.  We
are able to derive limits on flux from the source, starting about
33 min after the event, including the period during which BeppoSAX
detected an x-ray source (IAUC 6576).  No transient or persistent
flux has been detected from about 40 keV to 10 MeV.  Preliminary
post-burst limits (3 sigma, in units of 10E-5 photons cmE-2 sE-1
keVE-1) at about 40-80 keV are as follows:  Feb. 28.149-28.444 UT,
5.3; Feb. 28.473-28.630 (roughly the SAX interval), 8.3; and Feb.
28.149-Mar. 3.000, 2.2.  The limit on the flux in the day prior to
the burst (Feb. 27.124-28.107) is 3.7 x 10E-5.  The source position
was not continuously observed during these intervals.  The OSSE 40-
80-keV upper limit during the SAX accumulation is comparable to the
flux seen by SAX at 2-10 keV.  A single power law, consistent with
both the SAX observation and the OSSE limits up to 250 keV, must be
softer than photon spectral index -0.3."
     K. Hurley, Space Sciences Laboratory, Berkeley, on behalf of
the Ulysses Gamma-Ray Burst Team; E. Costa and M. Feroci, Istituto
Astrofisica Spaziale, CNR, Frascati; F. Frontera, Universita di
Ferrara and ITESRE, Bologna; and D. Dal Fiume and M. Orlandini,
ITESRE, Bologna, report:  "A triangulation of GRB 970228 has been
done using preliminary Ulysses and SAX GRBM data.  The resulting
position is an annulus whose half-width is conservatively estimated
to be 0.015 deg at 3-sigma confidence, centered at R.A. = 11h03m47s,
Decl. = +36o31'.5 (equinox 2000.0), with central radius 83.422 deg.
Combining this with the BeppoSAX error circle by Costa et al. (IAUC
6572) gives an approximately 6-arcmin**2 trapezoidal error box with
corners at R.A., Decl. = 5h01m49s, +11o44'.2; 5h01m46s, +11o45'.2;
5h02m00s, +11o43'.6; 5h01m46s, +11o48'.1.  Although this trapezoid
formally excludes the fading VLA source reported by Frail et al.
(IAUC 6576), the annulus alone is consistent with it and with the
MECS/LECS x-ray source reported by Costa et al.  Further processing
may result in a narrower annulus."

     Naked-eye m1 estimates by G. W. Kronk, Troy, IL:  Mar. 4.47
UT, 0.3; 6.47, 0.1; 7.47, 0.0; 8.46, 0.0.

                      (C) Copyright 1997 CBAT
1997 March 8                   (6578)            Daniel W. E. Green

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