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GCN Circular 153

Subject
SGR1900+14, BeppoSAX-GRBM observations
Date
1998-09-01T15:49:39Z (25 years ago)
From
Marco Feroci at IAS/CNR Frascati <feroci@ias.rm.cnr.it>
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."
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