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GCN Circular 8876

Subject
GRB 090131: Fermi GBM detection
Date
2009-02-03T03:23:47Z (15 years ago)
From
Adam Goldstein at Fermi-GBM/UAH <adam.m.goldstein@msfc.nasa.gov>
A. Goldstein (UAH) and A.J. van der Horst (NASA/MSFC/ORAU) report 
on behalf of the Fermi GBM Team: 

"At 02:09:21.15 UT on 31 January 2009, the Fermi Gamma-Ray Burst Monitor 
triggered and located GRB 090131 (trigger 255060563 / 090131090).

The on-ground calculated location, using the GBM trigger data, is 
RA = 353.0, DEC = +16.4 (J2000 degrees, equivalent to 23h 32m, 16d 26'), 
with a statistical uncertainty of less than 1 degree (radius, 1-sigma 
containment) and an additional systematic error which is currently 
estimated to be 2 to 3 degrees.
The angle from the Fermi LAT boresight is 40 degrees.

The GBM light curve consists of two emission pulses, each with 
substructure and separated by a period of no significant 
emission above background.  The total duration (T90) is about 
36.4 s (8-1000 keV).  The time-averaged spectrum from T0+0.0 s to 
T0+42.2 s is best fit by a Band function with 
Epeak = 58.4 +/- 3.9 keV, alpha = -1.27 +/- 0.07, and 
beta = -2.26 +/- 0.05 (chi-square 597.4 for 453 d.o.f.).

The event fluence (8-1000 keV) in this time interval is 
(2.23 +/- 0.17)E-05 erg/cm^2. The 1-sec peak photon flux measured 
starting from T0+6.4 s in the 8-1000 keV band 
is 47.9 +/- 10.0 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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