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GCN Circular 32851

GRB 221025A: Fermi GBM Observation
2022-10-25T16:52:20Z (a year ago)
Joshua Wood at MSFC/Fermi-GBM <>
J. Wood (NASA/MSFC) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 00:58:18 UT on 25 October 2022, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 221025A (trigger 688352303 / 221025040).
which was also detected by Fermi-LAT (Arimoto M. et al. 2022, GCN 32843).
The Fermi GBM on-ground location is consistent with the Fermi-LAT position.

The on-ground calculated location, using the GBM trigger
data, is RA = 128.9, DEC = +2.2 (J2000 degrees,
equivalent to 08h 36m, +02d 12'), with an uncertainty
of 6.8 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 is 48.5 degrees.

The GBM light curve consists of a single pulse with a duration (T90)
of about 0.4 s (50-300 keV). The time-averaged spectrum
from T0+0.0 to T0+0.8 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.4 +/- 0.1 and the cutoff energy,
parameterized as Epeak, is 1680 +/- 345 keV.

The event fluence (10-1000 keV) in this time interval is
(1.7 +/- 0.1)E-06 erg/cm^2. The 64-ms peak photon flux measured
starting from T0+0.3 s in the 10-1000 keV band is 13.3 +/- 0.9 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:

For Fermi GBM data and info, please visit the official Fermi GBM Support Page:"
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