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GCN Circular 9813

GRB 090815B: Fermi GBM detection
2009-08-15T14:48:04Z (15 years ago)
Andreas von Kienlin at MPE <>
A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: 

"At 10:30:41.85 UT on 15 August 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090815B (trigger 272025043 / Y090815438).

The on-ground calculated location, using the GBM trigger data, 
is RA = 21.4, DEC = 53.4 (J2000 degrees, equivalent to 01h 26m, 53d 24'), 
with an uncertainty of 5.7 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 82 degrees.

The GBM light curve consists of two peaks with a duration (T90) 
of about 30 s (8-1000 keV). The time-averaged spectrum from 
T0-7.168 s to T0+23.552 s is well fit by a power law function 
with an exponential high energy cutoff.  The power law index 
is -1.89 +/- 0.12 and the cutoff energy, parameterized as Epeak, 
is 15.1 +/- 10.8 keV (chi squared 297 for 238 d.o.f.).

The event fluence (8-1000 keV) in this time interval is 
(5.05 +/- 0.25)E-06 erg/cm^2. The 1.024-sec peak photon flux measured 
starting from T0+16.384 s in the 8-1000 keV band 
is 14.4 +/- 0.5 ph/s/cm^2.

A Band function fits the spectrum equally well (chi squared 296 
for 237 d.o.f.) with Epeak= 18.6 +/- 9.6 keV, alpha = -1.82 +/- 0.19 
and beta = -2.7 +/- 0.4. 

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