[vsnet-grb-info 8158] GRB 090718B: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9690
SUBJECT: GRB 090718B: Fermi GBM detection
DATE:    09/07/20 14:49:19 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 18:17:42.84 UT on 18 July 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090718B (trigger 269633864 / 090718762).
The on-ground calculated location, using the GBM trigger data, is
RA = 274.1, DEC = -36.4 (J2000 degrees, equivalent to 18h16m, -36d23'),
with an uncertainty of 1.2 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 76 degrees.

The GBM light curve consists of several peaks with
a duration (T90) of about 28 s (8-1000 keV).
The time-averaged spectrum from T0 to T0+29.7 s is well fit by
a power law function with an exponential high energy cutoff.  The
power law index is -1.21 +/- 0.02 and the cutoff energy, parameterized
as Epeak, is 198 +/- 9 keV (chi squared 507 for 480 d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(2.52 +/- 0.05)E-5 erg/cm^2. The 1-sec peak photon flux
measured starting from T0+21.5 s in the 8-1000 keV band
is 32.0 +/- 0.5 ph/s/cm^2.

A Band function fits the spectrum equally well (chi squared 504 for
479 d.o.f.) with Epeak = 184 +/- 9 keV, alpha = -1.18 +/- 0.03 and
beta = -2.59 +/- 0.26.

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