TITLE: GCN CIRCULAR NUMBER: 33389 SUBJECT: GRB 230228A: Fermi GBM Observation DATE: 23/03/01 16:12:06 GMT FROM: Cori Fletcher at USRA cfletcher@usra.edu
C. Fletcher (USRA), S. Lesage (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 05:50:51 UT on 28 February 2023, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 230228A (trigger 699256256/230228244). which was also detected by Swift BAT (S. Dichiara et al. 2023, GCN 33378). The Fermi GBM on-ground location is consistent with the Swift BAT position.
The angle from the Fermi LAT boresight is 114 degrees.
The GBM light curve consists of a single burst with a duration (T90) of about 2 s (10-1000 keV). The time-averaged spectrum from T0-0.9 to T0+1.5 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.8 +/- 0.3 and the cutoff energy, parameterized as Epeak, is 110 +/- 20 keV.
The event fluence (10-1000 keV) in this time interval is (5.9 +/- 0.6)E-07 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0 s in the 10-1000 keV band is 6 +/- 1 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/"