TITLE: GCN GRB OBSERVATION REPORT NUMBER: 159 SUBJECT: GRB 981220: RXTE/ASM and BeppoSAX/GRBM results DATE: 98/12/22 17:14:20 GMT FROM: Don Smith at MIT 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".]