GRB 090518B

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."

M.Cwiok, W.Dominik, G.Kasprowicz, A.Majcher, A.Majczyna,
K.Malek, L.Mankiewicz, K.Nawrocki, L.W.Piotrowski,
D.Rybka, M.Sokolowski, J.Uzycki, G.Wrochna, M.Zaremba, A.F.Zarnecki
on behalf of "Pi of the Sky" collaboration http://grb.fuw.edu.pl

The "Pi of the Sky" apparatus observed error box of Fermi GRB090518B
before, during and after the burst, starting 23 minutes before the
Fermi trigger. No new source brighter than 11 mag has been identified
on 10s exposures.