[vsnet-grb-info 7629] GRB 090418C: Fermi GBM Detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9184
SUBJECT: GRB 090418C: Fermi GBM Detection
DATE:    09/04/22 01:08:13 GMT
FROM:    Valerie Connaughton at MSFC  <valerie at nasa.gov>

Valerie Connaughton (UAH) reports on behalf of the Fermi GBM Team:

"At 19:35:24.92 UT on 18 April 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090418C (trigger 261776126 / 090418816).

The on-ground calculated location, using the GBM trigger
data, is RA = 262.8, DEC = -28.3 (J2000 degrees,
equivalent to 17 h 31 m, -28 d 18 '), with an uncertainty
of 14.4 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 58 degrees.

The GBM light curve shows a short, double-peaked burst
with a duration (T90) of about 0.6 s (8-1000 keV).
The time-averaged spectrum from T0-0.128 s to T0+0.256 s is
well fit by a power law with index -1.27 +/- 0.04, though
formally it is best fit by a power law function with an exponential
high energy cutoff.  The power law index in this case
is -0.94 +/- 0.08 and the cutoff energy, parameterized as Epeak,
lies above 1 MeV.

The event fluence (8-1000 keV) in this time interval is
(6.0 +/- 0.3)E-7 erg/cm^2. The 0.128-sec peak photon flux measured
starting from T0-0.128 s in the 8-1000 keV band
is 8.5 +/- 0.5 ph/s/cm^2.

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