GRB 090528

A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: 

"At 04:09:01.14 UT on 28 May 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090528 (trigger 265176543 / 090528173).
The on-ground calculated location, using the GBM trigger 
data, is RA = 134.9, DEC = -35.8 (J2000 degrees, 
equivalent to 09h 00m, -35d 48'), with an uncertainty 
of 3.4 degrees (radius, 1-sigma containment, 
statistical only; there is additionally a systematic
error which is currently estimated to be 2 to 3 degrees).
The GBM on-ground location is within two sigma of the 
Vela X-1 position, nevertheless we think this event 
is due to a real gamma-ray burst because intensity, duration 
and spectrum are unusual for Vela X-1 observed outburst.
 
The angle from the Fermi LAT boresight is 81 degrees.

The GBM light consists of one major structured pulse
with a duration (T90) of about 68 s (8-1000 keV). 
The time-averaged spectrum from T0-5.120  s to T0+29.696 s is 
well fit by a power law function with an exponential
high energy cutoff.  The power law index is -1.7 +/- 0.1 and
the cutoff energy, parameterized as Epeak, is 99 +/- 26 keV
(chi squared 357 for 359 d.o.f.).

The event fluence (8-1000 keV) in this time interval is 
(9.3 +/- 0.9)E-06 erg/cm^2. The 1-sec peak photon flux measured 
starting from T0+3.072 s in the 8-1000 keV band 
is 7.6 +/- 0.3 ph/s/cm^2.

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

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

The long GRB 090528 (Fermi/GBM trigger 265176543 / 090528173, von Kienlin et al.,
GCN 9446
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 ) was detected by the Suzaku Wide-band All-sky Monitor (WAM) which
covers an energy range of 50 keV - 5 MeV at 04:09:01.00 UT (=T0). The observed
light curve shows a single-peaked structure lasting from T0-8s, ending at T0+28s,
with a duration (T90) of about 26.0 seconds. 

The fluence in 100 - 1000 keV was 1.9 (+0.2/-0.7) * 10^-6 erg/cm^2.
The 1-s peak flux measured from T0+2.5s was 0.5 (+0.2/-0.3) photons/cm^2/s
in the same energy range.

Preliminary result shows that the time-averaged spectrum from T0-4s to T0+22s
is well fitted by a single power-law with a photon index of 2.6 (+0.7/-0.5)
(chi^2/d.o.f = 13/13). 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.ac.jp/suzaku/research/HXD-WAM/WAM-GRB/grb/untrig/grb_table.html