TITLE:   GCN CIRCULAR
NUMBER:  31928
SUBJECT: GRB 220418B Fermi GBM observation
DATE:    22/04/21 01:25:04 GMT
FROM:    Cori Fletcher at USRA  <cfletcher@usra.edu>

C. Fletcher (USRA), S. Dalessi (UAH) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 17:16:21.65 UT on 18 April 2022, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 220418B (trigger 671994986 / 220418720).
which was also detected by the Swift-BAT/GUANO (GCN 31919, 31921)
The Fermi GBM Final Real-time Localization (GCN 31915) is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 80 degrees.

The GBM light curve shows a single peak
with a duration (T90) of about 1.7 s (50-300 keV).
The time-averaged spectrum from T0-1.024 s to T0+1.024 s is
best fit a simple power law function with index -1.6 +/- 0.1.

The event fluence (10-1000 keV) in this time interval is
(3.8 +/- 0.6)E-07 erg/cm^2. The 64-ms peak photon flux measured
starting from T0-0.57 s in the 10-1000 keV band
is 121 +/- 76 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html

For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"