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GCN Circular 9688

GRB 090720: Fermi GBM detection
2009-07-20T14:44:23Z (15 years ago)
Arne Rau at MPE <>
Arne Rau (MPE) reports on behalf of the Fermi GBM Team:

"At 06:38:08.28 UT on 20 July 20009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090720 (trigger 269764690 / 090720276).

The on-ground calculated location, using the GBM trigger
data, is RA = 199.5, DEC = -16.4 (J2000 degrees,
equivalent to 13 h 18 m, -16 d 24 '), with an uncertainty
of 5.0 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 113 degrees.

This burst was also independently detected (but not triggered) by 

The GBM light curve shows a single peak
with a duration (T90) of about 7.0 s (8-1000 keV).
The time-averaged spectrum from T0-1.856 s to T0+5.312 s is
best fit by a power law function with an exponential
high energy cutoff.  The power law index is -0.75 +/- 0.10 and
the cutoff energy, parameterized as Epeak, is 117.50 +/- 7.12 keV
(chi squared 507 for 507 d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(2.9 +/- 0.1)E-06 erg/cm^2. The 1.024-sec peak photon flux measured
starting from T0+0.002 s in the 8-1000 keV band
is 10.9 +/- 0.3 ph/s/cm^2.

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