[vsnet-grb-info 7848] GRB 090518B: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9392
SUBJECT: GRB 090518B: Fermi GBM detection
DATE:    09/05/18 14:45:29 GMT
FROM:    Andreas von Kienlin at MPE  <azk at mpe.mpg.de>

A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: 

"At 05:51:04.67 UT on 18 May 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090518B (trigger 264318666 / 090518244).
The on-ground calculated location, using the GBM trigger 
data, is RA = 211.2, DEC = -16.7 (J2000 degrees, 
equivalent to 14h 05m, -16d 42'), with an uncertainty 
of 4.5 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 90 degrees.

The GBM light curve shows one structured peak
with a duration (T90) of about 12 s (8-1000 keV). 
The time-averaged spectrum from T0-0.768 s to T0+6.656 s is 
well fit by a power law function with an exponential
high energy cutoff.  The power law index is -0.74 +/- 0.13 and
the cutoff energy, parameterized as Epeak, is 127 +/- 12 keV
(chi squared 399 for 363 d.o.f.).

The event fluence (8-1000 keV) in this time interval is 
(2.2 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured 
starting from T0-0.256 s in the 8-1000 keV band 
is 5.6 +/- 0.6 ph/s/cm^2.

The spectrum can also be fit by using a Band function with 
Epeak = 86 +/- 15 keV and beta = -2.10 +/- 0.14. However alpha 
is poorly constrained.

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