GRB 091120

David Gruber (MPE) reports on behalf of the Fermi GBM Team: 


"At 04:34:40.23  UT on 20 November 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 091120 (trigger 280384482 / 091120191).

The on-ground calculated location, using the GBM trigger 
data, is RA = 224.8, DEC = -24.8 (J2000 degrees, 
equivalent to 14h 59m, -24d 48'), with an uncertainty 
of 1.32 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 45 degrees.
Moreover, this burst was bright enough to result in
a Fermi spacecraft repointing maneuver.

The GBM light curve consists of several peaks with a 
duration (T90) of about 52 s (8-1000 keV). 
The time-averaged spectrum from T0-3 s to T0+56 s is 
adequately fit by a power law function with an exponential
high energy cutoff.  The power law index is -1.17 +/- 0.02 and
the cutoff energy, parameterized as Epeak, is 129 +/- 3 keV.
(C-stat 691 for 362 d.o.f.).

The event fluence (8-1000 keV) in this time interval is 
(3.02 +/- 0.04)E-5 erg/cm^2. The 1-sec peak photon flux measured 
starting from T0+26.6 s in the 8-1000 keV band 
is 21.3 +/- 0.4 ph/s/cm^2.

A Band function fits the spectrum equally well (C-stat 687 for 361 d.o.f.) 
with Epeak= 124 +/- 4 keV, alpha = -1.15 +/- 0.02 
and beta = -2.98 +/- 0.27. 

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

M.Nakajima (Nihon U.), S.Nakahira (AGU), M.Sugizaki, M.Kohama(RIKEN),
M.Suzuki (ISAS/JAXA), A.Yoshida, K.Yamaoka (AGU), 
N.Kawai, M.Morii(Tokyo Tech), H.Negoro (Nihon U.), M.Matsuoka, H.Tomida,
S.Ueno(ISAS/JAXA), Y.Ueda, S.Eguchi (Kyoto U.) and H.Tsunemi (Osaka Univ.)  
on behalf of the MAXI team report:

The Gas Slit Camera (GSC) of MAXI detected a bright hard X-ray
transient at 04:34:56 on 20 November 2009 (UT).  This event should
correspond to a GRB detected by Fermi-GBM, INTEGRAL SPI-ACS
andKonus-Wind.

The location of the source derived from the GSC data is 
(R.A.,Dec.)=(226.81 deg, -21.79 deg)=(15:07:14.40, -21:47:24.0)(J2000) 
with an uncertainty of about 0.5 degree.  This is consistent with that
reported by Gruber (GCNC10187) within an error.

The GSC FOV scanned over the source from 04:34:56 (UT) (16 seconds
after the GBM trigger) for about 40 seconds.  The average X-ray flux
over the observation is 4.9x10^-8 erg/cm2/s in 3-15 keV.  Significant
intensity variation was clearly seen in the light curve. 

MAXI is currently under the commissioning phase and the systematic
uncertainty in localization will be significantly improved with the
progress of the alignment calibration.
This message may be citable.

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

The long GRB 091120 reported by Fermi GBM, (Gruber, GCN 10187
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 )
and localized by MAXI GSC (Nakajima et al., GCN 10188
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 )
triggered Konus-Wind at T0=16476.183 s UT (04:34:36.183).

The burst light curve consists of several peaks with a total
duration of ~55 s. The Konus-Wind light curve of this GRB
is available at http://www.ioffe.ru/LEA/GRBs/GRB091120_T16476/
Considerable hard to soft spectral evolution is noticed during the
initial part of the burst.

As observed by Konus-Wind the burst
had a fluence of 2.6(+/-0.3)x10-5 erg/cm2,
and a 256-ms peak flux measured from T0 + 25.344s
of 2.4(+/-0.3)x10-6 erg/cm2/s
(both in the 20 keV - 2 MeV energy range).

The time-integrated spectrum of the burst
(from T0 to T0+57.600 s) is well fitted
in the 20 keV - 2 MeV range by a power law
with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep), with
alpha = -1.2(-0.25, +0.28),
and Ep = 145(-18, +26) keV (chi2 = 67/61 dof).

The spectrum of the most intense peak (measured
from T0+24.832 to T0+33.024 s) is also well fitted
in the 20 keV - 2 MeV range by a power law
with exponential cutoff model, for which
alpha = -1.0(-0.4, +0.45),
and Ep = 101(-15, +16) keV (chi2 = 48/61 dof).


All the quoted results are preliminary.
All the quoted errors are at the 90% confidence level.

K. Hurley and T. Cline, on behalf of the Mars Odyssey
and Konus GRB teams,

I. G. Mitrofanov, D. Golovin, M. L. Litvak, and A. B. Sanin,
on behalf of the HEND-Odyssey GRB team,

W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr, on
behalf of the GRS-Odyssey GRB team,

S. Golenetskii, R. Aptekar, E. Mazets, V. Pal'shin, and D. Frederiks, 
on behalf of the Konus-Wind team,

V. Connaughton, M. Briggs, and C. Meegan, on
behalf of the Fermi-GBM team,

A. von Kienlin, G. Lichti, and A. Rau, on behalf of the
INTEGRAL SPI-ACS GRB team, 

D. M. Smith, R. P. Lin, J. McTiernan, R. Schwartz, C. Wigger, and W.
Hajdas, on behalf of the RHESSI GRB team, and 

G. Di Cocco, F. Fuschino, M. Galli, C. Labanti, and M. Marisaldi, 
on behalf of the AGILE MCAL team, report:

AGILE (MiniCalorimeter), INTEGRAL (SPI-ACS), Konus-Wind, and
Mars Odyssey (HEND) observed GRB091120 (Gruber et al. GCN 10187
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 ;
Nakajima et al. GCN 10188
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 ; Golenetskii et al. GCN 10189
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 ).  We
have triangulated this burst to an error ellipse which may be
approximated by the following preliminary, 3 sigma error box:

-----------------------------------------------
    RA(2000), deg              Dec(2000), deg
-----------------------------------------------
Center:
  227.393 (15h 09m 34s)   -19.849 (-19d 50' 56")
Corners:
  226.629 (15h 06m 31s)   -22.609 (-22d 36' 33")
  226.458 (15h 05m 50s)   -22.135 (-22d 08' 05")
  228.539 (15h 14m 09s)   -15.899 (-15d 53' 57")
  228.535 (15h 14m 08s)   -16.885 (-16d 53' 08")
-----------------------------------------------

The IPN-only error box area is approximately 6600 square
arcminutes, and is consistent with the MAXI error circle; 
the IPN/MAXI error box area is approximately 1000 square 
arcminutes.  This triangulation can be improved.

A figure showing the GBM, MAXI, and IPN localizations is
posted at ssl.berkeley.edu/ipn3/091120