GRB 090131

A. Goldstein (UAH) and A.J. van der Horst (NASA/MSFC/ORAU) report 
on behalf of the Fermi GBM Team: 

"At 02:09:21.15 UT on 31 January 2009, the Fermi Gamma-Ray Burst Monitor 
triggered and located GRB 090131 (trigger 255060563 / 090131090).

The on-ground calculated location, using the GBM trigger data, is 
RA = 353.0, DEC = +16.4 (J2000 degrees, equivalent to 23h 32m, 16d 26'), 
with a statistical uncertainty of less than 1 degree (radius, 1-sigma 
containment) and an additional systematic error which is currently 
estimated to be 2 to 3 degrees.
The angle from the Fermi LAT boresight is 40 degrees.

The GBM light curve consists of two emission pulses, each with 
substructure and separated by a period of no significant 
emission above background.  The total duration (T90) is about 
36.4 s (8-1000 keV).  The time-averaged spectrum from T0+0.0 s to 
T0+42.2 s is best fit by a Band function with 
Epeak = 58.4 +/- 3.9 keV, alpha = -1.27 +/- 0.07, and 
beta = -2.26 +/- 0.05 (chi-square 597.4 for 453 d.o.f.).

The event fluence (8-1000 keV) in this time interval is 
(2.23 +/- 0.17)E-05 erg/cm^2. The 1-sec peak photon flux measured 
starting from T0+6.4 s in the 8-1000 keV band 
is 47.9 +/- 10.0 ph/s/cm^2.

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

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 090131 (Goldstein et al., GCN 8876
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 ) triggered the
Suzaku Wide-band All-sky Monitor (WAM) which covers an energy
range of 50 keV - 5 MeV at 2009-01-31 02:09:24.187 UT (=T0).

The observed light curve shows a multi-peaked structure starting at T0-5s,
ending at T0+46s with a duration (T90) of about 32.6 seconds. The fluence in
100 - 1000 keV was 9.95(-0.59, +0.57) x 10^-6 erg/cm^2. The 1-s peak
flux measured from T0+19s was 5.01(-0.39, +0.35) photons/cm^2/s in the
same energy range.

Preliminary result shows that the time-averaged spectrum from T0-5s
to T0+46s is fitted by a single power-law with a photon index
of 2.29(-0.15, +0.17) (chi^2/d.o.f = 11.4/13).

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.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html