TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  2920
SUBJECT: Giant flare from SGR 1806-20 detected by INTEGRAL
DATE:    04/12/29 11:19:07 GMT
FROM:    Sandro Mereghetti at IASF/CNR  <sandro@mi.iasf.cnr.it>

J.Borkowski (CAMK, Torun), D. Gotz, S. Mereghetti (IASF, Milano),
N.Mowlavi, S.Shaw, M.Turler (ISDC, Versoix), report:

A large flare most likely coming from the soft repeater SGR 1806-20 has
been detected with INTEGRAL on December 27 at 21:30:26 UT.

The flare caused a large and rapid increase in the count rate of the SPI
ACS which reached a peak flux of 2x10^6 counts/s (compared to a
background level of 88,000 counts/s ).  The initial spike, lasting about
1.5 s, is followed by a 300 s long tail in which pulsations at 7.57 s are
clearly visible.  The IBAS ACS system triggered on a fainter event
occurring about 140 s before the main flare and possibly due to a
precursor from the same source.

No positional information is available with the SPI ACS data. The
shape of the light curve, similar to that of the 27 August 1998 flare
from SGR 1900+14, but with a  periodicity of 7.6 s, indicates
that SGR 1806-20 is the most likely origin of the observed event.
This would be the first giant flare observed from SGR 1806-20.

At the time of the flare, INTEGRAL was pointing at 106 degrees from the
direction of SGR 1806-20, which was outside the fields of view of the
imaging instruments.

See also the News section of  http://ibas.mi.iasf.cnr.it/
for further details of the ongoing analysis

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