TITLE: GCN GRB OBSERVATION REPORT NUMBER: 311 SUBJECT: GRB990510: NFI X-ray source DATE: 99/05/10 21:38:12 GMT FROM: Luigi Piro at IAS/CNR Frascati Luigi Piro (BeppoSAX Mission Scientist on behalf of the BeppoSAX team) report: BeppoSAX MAIL n. 99/8: GRB990510: possible X-ray afterglow A BeppoSAX follow-up of GRB990510 started about 8 hr after the burst. Preliminary analysis of the first two orbits of the MECS data at SOC shows a previously unknown strong source in the center of the WFC error circle. Preliminary coordinates are: R.A.(2000)= 204.605 DEC(2000)= -80.490 The error radius is 1.5' Considering its strength, this X-ray source is likely the X-ray afterglow of GB990510. BeppoSAX is continuing its observation.