E. Bissaldi (Politecnico & INFN Bari), C. Meegan (UAH) and
O.J. Roberts (USRA) report on behalf of the Fermi GBM Team:
"At 23:28:17.53 UT on 13 March 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180313A (trigger 542676502 / 180313978).
The on-ground calculated location, using the GBM trigger
RA, Dec = 317.51, -26.55 (J2000 degrees)
with an uncertainty of 5.7 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 trigger resulted in an Autonomous Repoint Request (ARR)
by the GBM Flight Software owing to the high peak flux
of the GRB. This ARR was accepted and the spacecraft slewed to the GBM in-flight
location. The initial angle from the Fermi LAT boresight to
the best location is 40 degrees.
The GBM light curve shows/consists of single peak
with a duration (T90) of about 0.1 s (50-300 keV).
The time-averaged spectrum from T0+0 s to T0+0.13 s is
best fit by a power-law function with an exponential
high-energy cutoff. The power law index is -0.26 +/- 0.21 and
the cutoff energy, parameterized as Epeak, is 287 +/- 44 keV
The event fluence (10-1000 keV) in this time interval is
(1.9 +/- 0.1)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 +/- 1 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."