GCN Circular 159

D. A. Smith (MIT) reports on behalf of the RXTE/ASM Team at MIT and
NASA/GSFC:

"The RXTE All-Sky Monitor has detected a hard X-ray flare, beginning
within a few seconds of 1998 December 20, 21:52:21 (UTC) and lasting
for about 20 s.  The flare consisted of a single symmetric peak that
reached a maximum flux (1.5-12 keV; 1-s bins) of 1.2+-0.1x10^-7 erg
cm^-2 s^-1.  The event was detected in a single camera and was
localized to an error box 5.0' x 60.0' (full width; 90% confidence
including a rough estimate of systematic error due to calibration
drift), centered on the position: R.A. = 03h43m01s, Decl. = +17o09'.0
(J2000.0) at a position angle of 75.54 degrees east of north.  This
position is inconsistent with any known X-ray sources. See
http://xte.mit.edu/grb/grb981220/ for a sky map and other relevent
plots."

M. Feroci and B. Preger (IAS/CNR, Rome), L. Amati, F. Frontera and M.
Orlandini (ITESRE/CNR, Bologna) report on behalf of the BeppoSAX/GRBM
Team:

"The BeppoSAX Gamma Ray Burst Monitor was triggered on 1998 December
20, 21:52:25.89365 UTC on a gamma-ray burst of about 15 s duration. The
preliminary estimated fluence in the 40-700 keV energy band is 1.0+-0.2
x 10^-5 erg cmE-2 sE-1, while its peak flux is about 10+-2 photons cmE-2 sE-1.
We therefore confirm that the event reported by the RXTE/ASM Team was
indeed a real GRB."

[GCN OP NOTE, 18:15 UT:  This archived copy of the Circular was edited
to fix the typo in the original distribution: "1.0+-0.2 erg cmE-2 sE-1"
was replaced with "1.0+-0.2 x 10^-5 erg cmE-2 sE-1".]
[GCN OP NOTE,  This archived copy of the Circular was edited to fix
a mistake in the original distribution:  the "degrees west of north"
was changed to "degrees east of north".]