TITLE: GCN GRB OBSERVATION REPORT NUMBER: 153 SUBJECT: SGR1900+14, BeppoSAX-GRBM observations DATE: 98/09/01 15:49:39 GMT FROM: Marco Feroci at IAS/CNR Frascati SGR 1900+14 M. Feroci, P. Soffitta, E. Costa, Istituto di Astrofisica Spaziale, CNR, Rome, and F. Frontera, Istituto Tecnologie e Studio Radiazioni Extraterrestri, CNR, Bologna, on behalf of the BeppoSAX/GRBM team, and M. Tavani, Istituto di Fisica Cosmica, CNR, Milano, and Columbia Astrophysics Laboratory, New York, report: "The Gamma-Ray Burst Monitor (GRBM) onboard BeppoSAX was triggered by the event reported by Cline et al. (IAUC 7002) on Aug. 27.4321259. The event showed a fast rise (<1s) and an exponential-like decay, lasting more than 300s. The event was observed at an off-set angle of about 56 degrees from the axis of GRBM unit 1, and showed a peak intensity in (40-700 keV) of about 64000 c/s. The event was clearly detected above 100 keV. A preliminary analysis shows that the spectrum is hard during the initial 1s, followed by a sudden softening. Subsequent spectral evolution shows a progressive hardening. The near-5s periodicity reported by Cline et al. (IAUC 7002) is evident in the GRBM data for the entire duration of the event. In addition, starting from about 35s after the event onset, the GRBM clearly detected a periodic pattern of subpulses for each near-5s oscillation. The repetitive pattern is made of four subpulses of period near-1s. More detailed temporal and spectral analyses are in progress."