Probable SGR or Short Duration GRB Detected by HETE
G. Ricker, D. Lamb, and S. Woosley on behalf of the HETE Science Team;
R. Vanderspek, G. Crew, J. Doty, G. Monnelly, J. Villasenor, N.
Butler, T. Cline, J.G. Jernigan, A. Levine, F. Martel, E. Morgan, G.
Prigozhin, J. Braga, R. Manchanda, and G. Pizzichini, on behalf of
the HETE Operations and HETE Optical-SXC Teams;
N. Kawai, M. Matsuoka, Y. Shirasaki, T. Tamagawa, K. Torii, T.
Sakamoto, A. Yoshida, E. Fenimore, M. Galassi, T. Donaghy, and C. Graziani, on
behalf of the HETE WXM Team;
J-L Atteia, M. Boer, J-F Olive, J-P Dezalay, and K. Hurley on behalf
of the HETE FREGATE Team;
At 05:06:30.61 UTC (18390.61 s UT) on 22 August, the HETE FREGATE
instrument detected a short, intense burst from a probable soft
gamma-ray repeater or (less likely) a short duration GRB. This event
was promptly distributed as a GCN Notice (HETE BID_1715). No signal
was detected in the WXM, indicating that the event was likely to
be >40 degrees from the anti-sun direction. For the current HETE
pointing direction, SGR1900+14 is about 48 degrees off the boresight,
while SGR1806-20 is about 56 degrees off the boresight, so that
either could be a candidate.
The burst duration in the 8-85 keV band was ~200 ms. A total of 500
counts were detected during that interval, corresponding to a fluence
of ~9 x 10-8 ergs cm-2 . The peak flux was >2 x 10-6 ergs cm-2 s-1
(ie >50 x Crab flux) over a duration of 30 ms.
A search for this event in the archives of other GRB instruments is
encouraged. This message is citeable.