S. Poolakkil (UAH) and C. Meegan (UAH) report on
behalf of the Fermi GBM Team:
"At 15:14:05.49 UT on 18 February 2018, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 180218A (trigger 540659650 / 180218635). This GRB
was also triangulated by IPN (Svinkin et al., GCN 22423).
The on-ground calculated location, using the GBM trigger
data, is RA = 47.23, DEC = 46.65, with an uncertainty
of 4 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 GBM light curve consists of a single bright peak
with a duration (T90) of about 6 s (50-300 keV).
The time-averaged spectrum from T0-1.02 s to T0+10.24 s is
best fit by a Band function with Epeak= 388 +/- 13 keV, alpha = -0.62 +/-
0.03 and beta = -2.36 +/- 0.06.
The event fluence (10-1000 keV) in this time interval is
(5.51 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+4.28 s in the 10-1000 keV band
is 65.9 +/- 0.86 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."