GRB 090617

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


"At 04:59:58.58 UT on 17 June 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090617 (trigger 266907600 / 090617208).
The on-ground calculated location, using the GBM trigger
data, is RA = 78.9, Dec = +15.7 (J2000 degrees,
equivalent to 05h 16m, 15d 42'), with an uncertainty
of 4.2 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 45 degrees.

The GBM light curve consists of a single bright pulse
with a duration (T90) of about 0.45 s (8-1000 keV).
The time-averaged spectrum from T0-0.032 s to T0+0.192 s is
best fit by a Band function with Epeak = 684 (-200/+250) keV,
alpha = -0.45 (-0.27/+0.17) and beta = -2.00 (-0.20/+0.24)
(Castor Stat 626 for 604 d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(4.68 +/- 0.20)E-07 erg/cm^2. The 32-msec peak photon flux
measured starting from T0-0.032 s in the 8-1000 keV band
is 10.0 +/- 0.5 ph/s/cm^2.


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

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

The short GRB 090617 (Fermi-GBM trigger 266907600 / 090617208;
Bissaldi et al., GCN 9523
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 ) triggered the Suzaku Wide-band All-sky 
Monitor (WAM) which covers an energy range of 50 keV - 5 MeV
at 04:59:58.105 UT (=T0).

The observed light curve shows a bright multi-peaked structure
starting at T0+0.45 s, ending at T0+0.6 s. 
The total T90 duration is about 0.14 seconds.

The fluence in 100 - 1000 keV was 8.8 (-5.9, +2.8)x10-7 erg/cm2.
The 1-s peak flux measured from T0 s was 1.7 (-1.0, +0.5) photons/cm2/s 
in the same energy range.

Preliminary result shows that the time-averaged spectrum from
T0 s to T0+1 s is well fitted by a power-law with exponential cutoff model:
  dN/dE ~  E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
  alpha       -0.02(-1.21, +1.07), and
  Epeak        698(+859, -171) keV (chi2/d.o.f. = 13.7/13).
 
All the quoted errors are at statistical 90% confidence level,
in which the systematic uncertainties are not included.
 
The light curves for this burst is available at:
http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html