GCN Circular 9895
Subject
GRB 090904B: Fermi GBM detection
Date
2009-09-04T22:01:47Z (15 years ago)
From
Adam Goldstein at Fermi-GBM/UAH <adam.m.goldstein@msfc.nasa.gov>
A. Goldstein (UAH) reports on behalf of the Fermi GBM Team:
"At 01:24:13.93 UT on 04 September 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090904B (trigger 273720255 / 090904058),
which was also detected by the SWIFT-BAT (D'Elia et al. 2009, GCN 9881).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 113 degrees.
The GBM light curve consists of three bright peaks
with a duration (T90) of about 71 s (8-1000 keV).
The time-averaged spectrum from T0-9.2 s to T0+65.5 s is
well fit by a power law function with an exponential
high energy cutoff. The power law index is 1.41 +/- 0.08 and
the cutoff energy, parameterized as Epeak, is 149.30 +/- 22.10 keV
(chi squared 243.6 for 238 d.o.f.).
The event fluence (8-1000 keV) in this time interval is
(2.44 +/- 0.15)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+21.5 s in the 8-1000 keV band
is 9.8 +/- 0.7 ph/s/cm^2.
A Band function fits the spectrum equally well
(chi squared 239.0 for 237 d.o.f.) with Epeak= 106.30 +/- 24.60 keV,
alpha = -1.26 +/- 0.15 and beta = -2.18 +/- 0.18.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."