[vsnet-grb-info 3656] Two bright bursts from SGR 1806-20 detected with IBAS

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  5490
SUBJECT: Two bright bursts from SGR 1806-20 detected with IBAS
DATE:    06/08/30 15:48:59 GMT
FROM:    Diego Gotz at IASF-CNR  <dgotz at cea.fr>

D. Gotz (CEA, Saclay) and S. Mereghetti (IASF, Milano), on behalf of the IBAS
Localization Team report:

The INTEGRAL Burst Alert System (IBAS) has detected several bursts from
SGR 1806-20 in the IBIS/ISGRI data, indicating that the source is in an
active state. We report here the properties of the two brightest and
longest bursts, that were detected on August 29, 2006, as well as the
times of the other events detected in the last few days.

The burst detected on Aug 29 at 21:57:43 UT was so bright to fully
saturate the ISGRI telemetry share after about 1 s. This burst was also
detected by the Anti-Coincidence System of the SPI instrument above ~80
keV, where it lasted 2 s. The 20-200 keV spectrum, derived from the the
available IBIS/ISGRI data, can be fitted with a Thermal Bremsstrahlung
(TB) model with a temperature of 22 keV. This is a typical value for the
SGR 1806-20 bursts, but the lower limit on its fluence ( 7E-7 erg/cmsq,
15-100 keV) places this burst among the brightest detected with INTEGRAL
(Gotz et al., 2006, A&A, 445, 313).

The second burst was detected at 22:10:28 UT and lasted 1.2 s. In this
case the telemetry was saturated only partially. The lower limit on the
fluence is 1E-6 erg/cmsq, and the TB temperature is 19 keV.

The times of all the recent IBAS triggers due to bursts from SGR 1806-20
are given below. For 15 of them automatic alert packets have been sent
(see Alerts #3437-3452 at http://ibas.iasf-milano.inaf.it).

2006-08-19T05:57:48

2006-08-25T21:03:31

2006-08-26T02:13:37
2006-08-26T03:23:35
2006-08-26T04:13:22
2006-08-26T04:25:25
2006-08-26T12:32:55
2006-08-26T18:48:47
2006-08-26T22:07:52

2006-08-27T03:14:45
2006-08-27T04:20:10
2006-08-27T08:49:52
2006-08-27T12:25:26
2006-08-27T12:41:34

2006-08-28T13:38:31

2006-08-29T21:57:43
2006-08-29T22:10:28
2006-08-29T22:48:01

2006-08-30T03:16:47
2006-08-30T14:58:39
2006-08-30T15:11:34

INTEGRAL will continue to monitor regularly the region of the Galactic Centre
(at least once every 3 days) until October 26th.

This message can be cited.