TITLE:   GCN CIRCULAR
NUMBER:  20835
SUBJECT: GRB 170307A: Fermi GBM observation   
DATE:    17/03/08 05:44:32 GMT
FROM:    C. Michelle Hui at MSFC/Fermi-GBM  <c.m.hui@nasa.gov>

C.M. Hui (NASA/MSFC) and O.J. Roberts (USRA/NASA)
report on behalf of the Fermi GBM Team:

At 20:25:17.49 UT on 07 March 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170307A (trigger 510611122 /170307851),
which was also detected by Swift BAT (A. Y. Lien et al., GCN 20832).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time 
using the Swift-BAT location is 98 degrees.

The GBM light curve consists of multiple peaks with a duration (T90) 
of about 57.9s (50-300 keV). The time-averaged spectrum 
from T0-27.6s to T0+28.7 s is adequately fit by a power law function 
with an exponential high-energy cutoff. The power law index 
is -1.18 +/- 0.26 and the cutoff energy, parameterized as Epeak, 
is 83.80 +/- 19.90 keV.

The event fluence (10-1000 keV) in this time interval is 
(1.85 +/- 0.25)E-06 erg/cm^2. The 1-sec peak photon flux measured 
starting from T0+8.3 s in the 10-1000 keV band is 
1.72 +/- 0.25 ph/s/cm^2.

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