TITLE:   GCN CIRCULAR
NUMBER:  20975
SUBJECT: GRB 170403A: Fermi GBM observation
DATE:    17/04/03 23:37:23 GMT
FROM:    Oliver J Roberts at USRA/NASA  <oliver.roberts@nasa.gov>

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

"At 13:59:17.80 UT on the 3rd of April 2017, the
Fermi Gamma-Ray Burst Monitor triggered and
located GRB 170403A (trigger 512920762 / 170403583).
The on-ground calculated location using the GBM
trigger data is,

RA = 267.08, DEC = +14.53 (J2000 degrees)

with an uncertainty of 7.16 degrees (radius, 1-sigma
containment, statistical only; there is additionally
a systematic error which we have characterized as a
core-plus-tail model, with 90% of GRBs having a 3.7 deg.
error and a small tail suffering a larger than 10 deg.
systematic error [Connaughton et al. 2015, ApJS, 216, 32]).

The angle from the Fermi LAT boresight at the GBM trigger
time is 88 degrees.

The GBM light curve consists of a short, bright GRB with
emission over a duration (T90) of about 1s
(50-300 keV). The time-averaged spectrum from T0-0.096 s to
T0+0.384 s is best fit by a power law function with an
exponential high-energy cutoff.  The power law index is
-1.01 +/- 0.14 and the cutoff energy, parameterized as
Epeak is 470 +/- 163 keV.

The event fluence (10-1000 keV) in this time interval is
(3.9 +/- 0.2)E-07 erg/cm^2. The 64 ms peak photon flux
measured starting from T0+0 s in the 10-1000 keV band
is 16.6 +/- 1.5 ph/s/cm^2.

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