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GCN Circular 8971

Subject
GRB 090309B: Fermi GBM detection
Date
2009-03-10T16:12:00Z (15 years ago)
From
Alexander van der Horst at NASA/MSFC <Alexander.J.VanDerHorst@nasa.gov>
A.J. van der Horst (NASA/MSFC/ORAU) reports on behalf of the
Fermi GBM Team:

"At 18:25:07.19 UT on 9 March 2009, the Fermi Gamma-ray Burst Monitor
(GBM) triggered and located GRB 090309B (trigger 258315909 / 090309.767).
The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 168.4, Dec = -55.0 (J2000 degrees, equivalent to
J2000 11h13m, -55d01'), with a statistical uncertainty of 2.6 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 26 degrees.

The GBM light curve consists of two main peaks, with durations of ~10
and ~25 seconds, and no significant emission above background level in
between for ~25 seconds. The time-averaged spectrum over the two peaks,
from T0-4.1 to T0+5.1 s and from T0+32.8 to T0+54.3 s, is best fit by
a power law with an exponential high-energy cutoff. The index is
-1.52 +/- 0.10 and the cutoff energy, parameterized as Epeak, is
197 +/- 65 keV (chi squared 358 for 360 d.o.f.). The fluence
(8-1000 keV) in this time interval is (4.7 +/- 0.4)E-6 erg/cm^2.
The 1-sec peak photon flux measured starting from T0+37.9s in the
8-1000 keV band is 4.43 +/- 0.17 ph/s/cm^2.

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