GCN Circular 1060

X-ray precursors to the large flare from SGR 1900+14

M. Feroci (IAS/CNR, Rome), J.J.M. in 't Zand (Astronomical Institute,
Utrecht University and SRON), P. Soffitta (IAS/CNR, Rome), K. Hurley
(UCB, California), F. Frontera (Univ. Ferrara and TESRE/CNR, Bologna)
and E. Mazets (IOFFE, S. Petersburg), report:

"A high-time resolution analysis has been performed of the BeppoSAX
Wide Field Camera data of SGR 1900+14 taken on April 18, 2001, when
the most recent giant flare was detected (Guidorzi et al., GCN 1041
Not found
 
 

and IAUC 7611). The data cover a short intermediate pointing of Wide
Field Camera unit 1 between two scheduled targets. The observation
started 2780 s before the giant flare and ended with the automatic
switch off due to that flare. The observation was interrupted when
BeppoSAX traversed the SAA, from 2282 till 1052 s before the
giant flare. The analysis revealed the presence of 3 short X-ray
precursors, occurring 2537, 755, and 444 s before the giant flare
(respectively, 25975, 27757 and 28068 s UT), with durations of 100,
125 and 55 ms, peak fluxes in excess of 20 Crab units (2-28 keV),
and 9-28/2-9 keV spectral hardness ratios that are consistent with
power laws with photon indices between roughly 0.5 and 1.2. None of the
precursors was detected in the gamma-ray data from the BeppoSAX/GRBM,
the gamma-ray burst detector on Ulysses, and from Konus on Wind."