GRB 091123

S. McBreen (UCD/MPE), V. Connaughton (UAH), C. Wilson-Hodge (NASA MSFC),
M. Finger (USRA) and D. Tierney (UCD) report on behalf of the Fermi GBM Team:

"At 07:08:37.26 UT on 23 November 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 091123 (trigger 280652919 / 091123298).
The on-ground calculated location, using the GBM trigger
data, is RA = 297.1, DEC = -29.2 (J2000 degrees,
equivalent to 19 h 48 m, -29 d 12'), with an uncertainty
of 2.4 degrees (radius, 1-sigma containment,
statistical only; there is additionally a systematic
error which is currently estimated to be 2 to 3 degrees).
The angle from the Fermi LAT boresight is 106 degrees.
This burst was also independently detected by INTEGRAL SPI-ACS
and Konus-Wind.

The GBM light curve consists of 4 main emission phases,
each containing structure, separated by long periods of quiescence.
Comparison with Konus-Wind data shows that the the event was
already on-going when when it rose above the Earth's horizon.
This allows a further constraint to be placed on the possible
arrival direction of this burst. A plot showing the 3-sigma
localization contours (statistical only) and the limb of
the Earth at T0, T0-5, and T0+5 s is available at:

http://gammaray.nsstc.nasa.gov/gbm/science/loc_091123298.gif


In the GBM data alone, the burst has  a duration of at least
650 sec (8-1000 keV).

The time-averaged spectrum from T0-5 s to T0+650 s is
adequately fit by a power law function with an exponential
high energy cutoff.  The power law index is -1.08 +/- 0.05 and
the cutoff energy, parameterized as Epeak, is 101.30 (+5.16/-4.52) keV
(C-stat 1008 for 355 d.o.f.). There is significant spectral
evolution within the fitted time interval.

The event fluence (8-1000 keV) in this time interval is
(4.07 +/- 0.09)E-05erg/cm^2. The 1-sec peak photon flux measured
starting from T0+11.2 s in the 8-1000 keV band
is 6.1 +/- 0.2 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

We thank Valentin Pal'shin for providing the Konus-Wind
lightcurves and informing us of the burst occultation by
the Earth before the GBM trigger time.

S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, P.
Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the Konus-Wind
team report:

A very long GRB 091123 was detected by Konus-Wind in the waiting mode at 
~T0=25585 s UT (07:06:25). The most part of the burst was also detected 
and localized by Fermi-GBM, while it missed the first ~130 s due to the 
Earth occultation (McBreen et al., GCN 10226
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 ).

The burst light curve shows several pulses with a total duration of ~800 s.

As observed by Konus-Wind, the burst had a fluence of (8.3 +/-
0.8)x10^-5 erg/cm2 (in the 20 - 1300 keV energy range).

Modeling the K-W 3-channel time-integrated spectrum (from T0 to T0+806 
s) by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha = -1.49 +/- 0.36, Ep = 243 +/- 80 keV.
The 3-channel spectrum of the most intense pulse
(from T0+100 s to T0+150 s) can be modeled by a power law with 
exponential cutoff model with alpha = -1.03 +/- 0.11, Ep = 293 +/- 35 
keV. The fluence of this pulse is (3.17 +/- 0.16)x10^-5 erg/cm2.

All the quoted errors are estimated at the 1 sigma confidence level.

The K-W light curve of this burst is available at
http://www.ioffe.rssi.ru/LEA/GRBs/GRB091123/

N. Ohmori, E. Sonoda, K. Kono, H. Hayashi, A. Daikyuji, Y.Nishioka,
K. Noda, M. Yamauchi (Univ. of Miyazaki), M. Ohno, M. Suzuki, 
M. Kokubun, T. Takahashi (ISAS/JAXA), K. Yamaoka (Aoyama  Gakuin U.),
S. Sugita (Nagoya U.), T. Sugasahara, M. Tashiro, Y. Terada, A. Endo, 
K. Onda, W. Iwakiri (Saitama U.), Y. E. Nakagawa, T. Tamagawa (RIKEN), 
N. Vasquez (Tokyo Tech.), Y. Urata, H.M  Lin (NCU), Y. Hanabata, 
T. Uehara, T. Takahashi, Y. Fukazawa (Hiroshima U.), T. Enoto, 
K. Nakazawa, K. Makishima (Univ. of Tokyo), S. Hong (Nihon U.), 
on behalf of the Suzaku WAM team, report

The very long GRB 091123 (Fermi-GBM trigger #280652919 / 091123298; 
McBreen et al., GCN 10226
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 ) was detected by the the Suzaku Wide-band 
All-sky Monitor (WAM) which covers an energy range of 50 keV - 5 MeV 
at 07:07:42 UT (=T0).

The observed light curve shows several pulses with a total duration of 
at least 650 s. The first bright emission episode was seen starting at 
T0-90 s, ending at T0+90 s. After the emission returned to the background 
level, three pulses was observed again at T0+220 s, T0+450 s, and T0+600 s, 
respectively.

The fluence in 100 - 1000 keV was 3.78 (-0.59, +0.45) x10^-5 erg/cm^2.
The 1-s peak flux measured from T0+45s was 2.08 (-0.31, +0.27) photons/cm^2/s
in the same energy range.

Preliminary result shows that the time-averaged spectrum from T0-90s to
T0+607s is fitted by a single power-law with a photon index
of 2.30 (-0.14, +0.16) (chi^2/d.o.f. = 63.4/99).

All the quoted errors are at statistical 90% confidence level,
in which the systematic uncertainties are not included.


The light curves with 1-sec time resolution for this burst will be appeared at:

http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/untrig/grb_table.html