GRB 090227B

S. Guiriec (UAH)
reports on behalf of the Fermi GBM Team:

"At 18:31:01.41 UT on 27 February 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located the short and bright GRB 090227B
(trigger 257452263 / 090227772).

The on-ground calculated location, using the GBM trigger data, is
RA = 11.81, Dec = +32.17 (J2000 degrees, equivalent to 11h48m36,+32d10'12),
with an uncertainty of 1.77 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 72 degrees.

This burst was also independently detected by INTEGRAL SPI-ACS.

The GBM light curve consists of one spike with a duration (T90) of about
0.9 s (10-1000 keV).
The time-averaged spectrum from T0-0.1s to T0+0.4s is best fitted by a Band
function with Epeak = 2255 +/- 116 keV,  alpha = -0.53 +/- 0.02, and
beta = -3.04 +/- 0.23 (chi squared 673 for 607 d.o.f.).

The event fluence (10-1000 keV) in this time interval is
(0.87 +/- 0.01)E-05 erg/cm^2. The 1-sec peak photon flux measured starting
from T0 in the 10-1000 keV band is 34.6 +/- 0.3 ph/s/cm^2.

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

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,

K. Yamaoka, M. Ohno, Y. Fukazawa, T. Takahashi, M. Tashiro, Y. Terada,
T. Murakami, K. Makishima, and Y. Hanabata on behalf of the Suzaku-WAM team,

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

A. von Kienlin, G. Lichti, and A. Rau, and K. Hurley on behalf of the
INTEGRAL SPI-ACS team report:

Konus-Wind, INTEGRAL-SPI-ACS, and Suzaku-WAM observed the bright short
hard GRB 090227B at about 18:31:00 UT (corresponding to the Fermi/GBM
trigger 257452263 / 090227772: Guiriec, GCN 8921
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 ).

The burst light curve shows a single pulse with a duration of ~0.2 sec.

Triangulation gives a Konus-WAM annulus centered at RA(2000)=336.619
(22h 26m 29s) Dec(2000)=-16.013 (-16d 00' 46"), whose radius is 56.968
�0.097 deg (3 sigma), and a Konus-SPI-ACS annulus centered at
RA(2000)=337.423 (22h 29m 42s) Dec(2000)= -19.538 (-19d 32' 16"), whose
radius is  59.273 � 0.224 deg (3sigma). These annuli intersect at
grazing incidence to form two long error boxes, one of which may be
eliminated by the GBM location (Guiriec, GCN 8921
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 ).
The resulting error box has the coordinates:
-----------------------------------------------------
       RA(2000), deg              Dec(2000), deg
-----------------------------------------------------
Center:
    13.499 (00h 54m 00s)   +28.401 (+28d 24' 05")
Corners:
    8.168 (00h 32m 40s)   +32.167 (+32d 10' 02")
   11.644 (00h 46m 34s)   +30.005 (+30d 00' 20")
   17.745 (01h 10m 59s)   +24.579 (+24d 34' 44")
   15.181 (01h 00m 43s)   +26.796 (+26d 47' 46")
-----------------------------------------------------

The error box area is 1.531 sq. deg.

This error box may be improved.

We have also derived a Konus-GBM annulus for the burst which is fully 
consistent with the Konus-WAM annulus.

The GBM location is consistent with the IPN box.
The center of the GBM location lies 1.830 deg from the Konus-WAM annulus
and 4.041 deg from the center of the box.
You can find the GBM confidence contours overplotted on the IPN box at 
the IPN triangulation map. The contours should be considered as 
preliminary and we expect the GBM localization code will be
refined. No systematic error has been added.

The Konus-Wind light curve of this GRB and IPN triangulation map is
available at http://www.ioffe.ru/LEA/GRBs/GRB090227_T66659/

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:

The bright short hard GRB 090227B (Fermi/GBM trigger 257452263 /
090227772: Guiriec, GCN 8921
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 ) localized by IPN (Golenetskii et al., GCN
8925
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 ) triggered Konus-Wind at T0=66659.079 s UT (18:30:59.079).

As observed by Konus-Wind the burst
had a fluence of (2.75 +/- 0.27)x10^-5 erg/cm2,
and a 16-ms peak flux measured from T0+0.008 s
of 3.98(-0.58, +0.59)x10^-4 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst
(from T0 to T0+0.192 s) is well fitted (in the 20 keV - 10 MeV
range) by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.43(-0.09, +0.10),
and Ep = 2253(-262, +292) keV (chi2 = 29.4/47 dof).
Fitting by GRB (Band) model yields:
the low-energy photon index alpha = -0.41(-0.10, +0.12),
the high energy photon index beta < -2.5,
the peak energy Ep = 2134(-326, +332) keV (chi2 = 28.1/46 dof).

The emission is clearly seen up to 10 MeV.

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