TITLE: GCN GRB OBSERVATION REPORT NUMBER: 224 SUBJECT: GRB 990123: BATSE Observations DATE: 99/01/25 22:18:55 GMT FROM: R. Marc Kippen at BATSE/UAH/MSFC R. M. Kippen (University of Alabama in Huntsville) reports on behalf of the BATSE GRB team: GRB 990123 was detected by BATSE on 1998 January 23.407594 as trigger number 7343. The event was strong and consisted of a multi-peaked temporal structure lasting >100 s, with significant spectral evolution. The T50 and T90 durations are 29.82 (-/+ 0.10) s and 63.30 (-/+ 0.26) s, respectively. The burst's peak flux (50-300 keV; integrated over 1.024 s) and fluence (>20 keV) are 16.42 (-/+ 0.12) photons cmE-2 sE-1 and 5.09 (-/+ 0.02) x 10E-4 erg cmE-2, respectively---ranking it in the top 2% (0.3%) of the BATSE burst flux (fluence) distribution. The average spectral hardness of the burst, as estimated by the ratio of 100-300 keV counts to those in the 50-100 keV range, is H32 = 1.51 (-/+ 0.004), which is average among BATSE bursts. The BATSE burst location is consistent with those measured by BeppoSAX (GCN 199,202,203) and with the proposed optical/radio transient counterpart (GCN 201; 204-221). A location sky-map and lightcurve for this event (and other notable bursts) are available at the BATSE Rapid Burst Response world-wide-web site: http://www.batse.msfc.nasa.gov/~kippen/batserbr/ -eof-