GRB 090428B

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


"At 13:15:11.06 UT on 28 April 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090428B (trigger 262617313 / 090428552).
The on-ground calculated location, using the GBM trigger
data, is RA = 0.8, DEC = +6.5 (J2000 degrees,
equivalent to 00h 03m, 06d 30'), with an uncertainty
of 4.4 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 101 degrees.

The GBM light curve consists of a broad single peak
with a duration (T90) of about 30 s (8-1000 keV).
The time-averaged spectrum from T0-9.2 s to T0+15.3 s is
adequately fit by a power law function with an exponential
high energy cutoff. The power law index is -1.86 +/- 0.07
and the cutoff energy, parameterized as Epeak,
is 65 +/- 16 keV (chi squared 279 for 241 d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(5.2 +/- 0.3)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+3.1 s in the 8-1000 keV band
is 10.1 +/- 0.7 ph/s/cm^2.

A Band function fits the spectrum equally well
(chi squared 278 for 240 d.o.f.) with Epeak = 53 +/- 19 keV,
alpha = -1.81 +/- 0.13 and beta = -2.17 +/- 0.21.


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

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),
K. Yamaoka, S. Sugita (Aoyama Gakuin U.), Y. E. Nakagawa,
T. Tamagawa (RIKEN), S. Hong (Nihon U.), N. Vasquez (Tokyo Tech.),
on behalf of the Suzaku WAM team, report:

The long GRB 090428B (Fermi/GBM
trigger 262617313 / 090428552, Bissaldi et al., GCN 9295
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 )
triggered the Suzaku Wide-band  All-sky Monitor (WAM) which covers an
energy range of 50 keV - 5 MeV at 13:15:12.66 UT (=T0).
The observed light curve shows a single FRED-like peak
starting at T0-10s, ending at T0+9s, with a duration (T90) of about 19.0 seconds. 

The fluence in 100 - 1000 keV was 2.6(+0.5/-0.9) X10^-6 erg/cm^2.
The 1-s peak flux measured from T0+1s was 1.1 photons/cm^2/s in the same
energy range.

Preliminary result shows that the time-averaged spectrum from T0-10s to
T0+9s is well fitted by a single power-law with a photon index
of 2.0 (+0.5/-0.4) (chi^2/d.o.f = 5/7).
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