GCN Circular 9366
Subject
GRB 090509: Fermi GBM observation
Date
2009-05-15T15:33:09Z (15 years ago)
From
Andreas von Kienlin at MPE <azk@mpe.mpg.de>
A. von Kienlin (MPE) and Sheila McBreen (UCD/MPE)
report on behalf of the Fermi GBM Team:
"At 05:10:05.72 UT on 09 May 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090509 (trigger 263538607 / 090509215)
which was also detected by the SWIFT-BAT (Grupe et al. 2008, GCN 9325;
Krimm et al., GCN 9349). The GBM on-ground location is consistent
with the Swift position.
The angle from the Fermi LAT boresight is 75 degrees.
The GBM light curve consists of two widely separated multi-peaked
emission periods with a duration (T90) of about 295 s (8-1000 keV).
The time-averaged spectrum of the first emission complex from
T0-3.072 to T0+24.576 s is well fit by a power law function with
an exponential high energy cutoff. The power law index is -0.90 +/- 0.16
and the cutoff energy, parameterized as Epeak, is 343 +/- 93 keV
(chi squared 375 for 360 d.o.f.).
The time-averaged spectrum of the second emission complex from
T0+239.619 s to T0+288.772 s is best fit by a simple power
law function with index -1.55 +/- 0.07 (chi squared 328 for 361 d.o.f.).
The summed event fluence (8-1000 keV) of both time intervals is
(8.4 +/- 0.4)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+18.432 s in the 8-1000 keV band
is 3.1 +/- 0.3 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."