[vsnet-grb-info 7874] GRB 090516C: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9418
SUBJECT: GRB 090516C: Fermi GBM detection
DATE:    09/05/21 23:32:21 GMT
FROM:    Alexander van der Horst at NASA/MSFC  <Alexander.J.VanDerHorst at nasa.gov>

A.J. van der Horst (NASA/MSFC/ORAU) reports on behalf of the
Fermi GBM Team:

"At 20:28:40.05 UT on 16 May 2009, the Fermi Gamma-ray Burst Monitor
(GBM) triggered and located GRB 090516C (trigger 264198522 / 090516.853).
The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 15.7, Dec = -13.7 (J2000 degrees, equivalent to
J2000 1h03m, -13d41'), with a statistical uncertainty of 3.5 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 69 degrees.

The GBM light curve consists of one short spike and some smaller peaks,
with a total duration (T90) of 15 s (8-1000 keV). The time-averaged
spectrum from T0+0.00 to T0+15.26 s is adequately fit by a power law
with an exponential high-energy cutoff. The index is -1.51 +/- 0.08
and the cutoff energy, parameterized as Epeak, is 210 +/- 68 keV
(chi squared 372 for 360 d.o.f.). The Band function provides a
significantly better fit (chi squared 365 for 359 d.o.f.) with a lower
Epeak value, but the low-energy index alpha and the amplitude are
poorly constrained: alpha is -0.44 +/- 0.81, beta is -1.81 +/- 0.06,
and Epeak is 38 +/- 14.
The fluence (8-1000 keV) in this interval is (4.0 +/- 0.3)E-6 erg/cm^2.
The 1-sec peak photon flux measured starting from T0+0.0s in the
8-1000 keV band is 7.7 +/- 0.4 ph/s/cm^2.

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