GRB 090227, GRB 090227A

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

The long GRB 090227A (Bissaldi et al., GCN 8917
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 ) triggered the
Suzaku Wide-band All-sky Monitor (WAM) which covers an energy
range of 50 keV - 5 MeV at 07:25:56.862 UT (=T0).

The observed light curve shows a multi-peaked structure starting at T0-1s,
ending at T0+17s with a duration (T90) of about 12.7 seconds. The
fluence in 100 - 1000 keV was 8.00(-1.41, +0.36) x 10^-6 erg/cm^2. The
1-s peak flux measured from T0+1s was 2.27(-1.00, +0.14)
photons/cm^2/s in the same energy range.

Preliminary result shows that the time-averaged spectrum from T0-1s
to T0+17s is fitted by a power-law with exponential cutoff model:

 dN/dE ~  E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
 alpha       1.16(-0.28, +0.22), and
 Epeak       1328(-465, +951) keV (chi^2/d.o.f. = 6.73/14).

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

The light curves for this burst are available at:
http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html

E. Bissaldi (MPE) reports on behalf of the Fermi GBM Team: 


"At 07:25:57.00 UT on 27 February 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090227 (trigger 257412359 / 090227310).
The on-ground calculated location, using the GBM trigger
data, is RA = 3.2, DEC = -43.1 (J2000 degrees,
equivalent to 00h 13m, -43d 06'), with an uncertainty
of 1.2 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 21 degrees.

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

The GBM light curve shows one main FRED-like pulse with substructure.
Emission continues to at least 80 seconds.
T90 (8-1000 keV) is about 50 s and T50 (8-1000 keV) is about 20 s.
The time-averaged spectrum from T0 to T0+16.3 s is
adequately fit by a power law function with an exponential
high energy cutoff.  The power law index is -0.91 +/- 0.06 and
the cutoff energy, parameterized as Epeak, is 1355 +/- 259 keV
(chi squared 748 for 729 d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(9.0 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.9 s in the 8-1000 keV band
is 4.57 +/- 0.13 ph/s/cm^2.

A Band function fits the spectrum equally well (chi squared 
748 for 728 d.o.f.) with Epeak = 1357 +/- 284 keV, 
alpha = -0.92 +/- 0.06 and beta = -3.6 +/- 2.9.


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