TITLE:   GCN CIRCULAR
NUMBER:  31955
SUBJECT: GRB 220426A: Fermi GBM detection
DATE:    22/04/26 19:42:53 GMT
FROM:    Christian Malacaria at NASA-MSFC/USRA  <cmalacaria@usra.edu>

C. Malacaria (USRA) and C. Meegan (UAH) report on behalf of the Fermi GBM Team:

At 06:49:51.23 UT on 26 April 2022, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 220426A (trigger 672648596 / 220426285).

The on-ground calculated location, using the GBM trigger data,
is RA = 335.8, DEC = -20.5 (J2000 degrees, equivalent
to 22h 23m, -20d 30'), with an uncertainty of 1.0 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 76 degrees.

The GBM light curve consists of a double pulse on top of a broader peak
with a duration (T90) of about 6 s (50-300 keV).
The time-averaged spectrum from T0+0.002 s to T0+9.856 s is
best fit by a Band function with Epeak = 146.3 +/- 0.9 keV,
alpha = -0.05 +/- 0.01, and beta = -3.08 +/- 0.04 .

The event fluence (10-1000 keV) in this time interval is
(1.084+/-0.005)E-04 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+3.9 s in the 10-1000 keV band
is 180.7 +/- 0.9 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/