TITLE:   GCN CIRCULAR
NUMBER:  31829
SUBJECT: GRB 220403B: Fermi GBM detection
DATE:    22/04/04 15:12:37 GMT
FROM:    Rachel Hamburg at UAH  <rkh0007@uah.edu>

Rachel Hamburg (UAH) and Boyan Hristov (UAH)
report on behalf of the Fermi GBM Team:

"At 20:42:39.05 UT on 03 April 2022, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 220403B (trigger 670711364 / 220403863), which
was also detected by the Swift/BAT and the Swift/XRT (Klingler et al. 2022,
GCN 31820). Additionally, the optical afterglow was detected by the
Swift/UVOT (Klingler et al. 2022, GCN 31820), D50 (Jelinek et al. 2022,
GCN 31821), Nanshan/NEXT (Zhu et al. 2022, GCN 31823) and LBT (Rossi 2022,
GCN 31826).

The angle from the Fermi LAT boresight at the GBM trigger time is 43
degrees.

The GBM light curve shows broad rise with multiple peaks with a
duration (T90) of about 28 s (50-300 keV).

The time-averaged spectrum from T0-6.1 s to T0+21.5 s is best fit by a
power law function with an exponential high-energy cutoff. The power law
index is -1.2 +/- 0.1 and the cutoff energy, parameterized as Epeak,
is 79 +/- 3 keV. The spectrum is also well fit by a Band function with
Epeak = 70 +/- 5, alpha = -1.1 +/- 0.1, and beta = -2.6 +/- 0.2.

The event fluence (10-1000 keV) in this time interval is
(5.2 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+7.6 s in the 10-1000 keV band is 4.3 +/- 0.2 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/"