[vsnet-grb-info 5068] Intense burst from SGR 1806-20 detected on September 7

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6775
SUBJECT: Intense burst from SGR 1806-20 detected on September 7
DATE:    07/09/10 16:59:15 GMT
FROM:    Valentin Pal'shin at Ioffe Inst  <val at mail.ioffe.ru>

S. Golenetskii, R. Aptekar, E. Mazets, V. Pal'shin, D. Frederiks,
and T. Cline on behalf of the Konus-Wind team,

J. Cummings, S. Barthelmy, N. Gehrels, H. Krimm, and D. Palmer
on behalf of the Swift-BAT team,

K. Hurley, A. von Kienlin, G. Lichti, A. Rau, D. Gotz, and
S. Mereghetti, on behalf of the INTEGRAL GRB team,
report:

An intense, short SGR-like event triggered Konus-Wind
at 2007-09-07 T0=60387.314 s UT (16:46:27.314).
It was also detected by Swift-BAT (out FoV) and INTEGRAL-SPI-ACS.
It was not detected by any other IPN spacecraft.

We have triangulated this burst to the Konus-BAT annulus
centered at RA(2000)=330.018 (22h 00m 04s)  Dec(2000)=-7.254 (-7d 15' 
14"), whose radius is 57.445 +/- 0.407 deg (3 sigma)
and to the Konus-SPI-ACS annulus
centered at RA(2000)=328.332 (21h 53m 20s)  Dec(2000)=-1.259 (-1d 15' 
31"), whose radius is 58.080 +/- 0.653 deg (3 sigma).
The center lines of these annuli pass 0.041 deg from the position of SGR 
1806-20 (correspondingly 0.3 and 0.2 sigma). They are inconsistent with 
the positions of all other known SGRs. The Konus ecliptic latitude 
response indicates that the source of the burst is near the ecliptic 
plane. Thus we conclude that this burst originated from SGR 1806-20.

The burst light curve shows a ~30-ms long spike at T-T0 ~-0.240 s 
followed by the main pulse with a duration of ~2 s, and
a small hump at T-T0 ~5.9 s with a duration of ~100 ms.
The Earth-crossing time of the first spike was 60384.6 s UT (16:46:24.6).

As observed by Konus-Wind the burst had a fluence of
1.47(-0.05, +0.04)x10^-5 erg/cm2, and a 16-ms peak flux
measured from T0+0.016 s of (1.67 +/- 0.21)x10^-5 erg/cm2
(both in the 20-200 keV range).

The spectrum of the burst (from T0 to T0+8.448) can be fitted
(in the 20-200 keV range) by the OTTB spectral model:
dN/dE ~ E^{-1} exp(-E/kT)
with kT = 20.9 +/- 0.9 keV (chi2 = 36/27 dof).

All the quoted errors are at 90% c.l.

The Konus-Wind light curve of this burst is available
at http://www.ioffe.rssi.ru/LEA/SGRs/070907_T60387/

The last burst from SGR 1806-20 to trigger Konus-Wind
was on July 27, 2007 (Golenetskii et al., GCN 6684).

Additional smaller bursts have been detected by BAT at
2007-09-09 22:45:36 and 2007-09-10 05:31:06 UT.