GCN Circular 38668

R. Sonawane (IISER, TVM) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 12:08:46.63 UT on 23 December 2024, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 241223A (trigger 756648531/241223506).

The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 159.85, Dec = -34.80 (J2000 degrees, equivalent to
J2000 10h 39m, -34d 47'), with a statistical uncertainty of 1.00 degrees.
(radius, 1-sigma containment, statistical only; there is additionally a
systematic error which we have characterized as a mixture of two Gaussians,
one with a radius of 1.8 degrees (52% contribution) and one with a radius
of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]).

The angle from the Fermi LAT boresight is 67 degrees.

The GBM light curve consist of one weak emission episode (possibly a precursor) followed by a strong emission episode with a duration (T90)
of about 30.5 s (50-300 keV). The time-averaged spectrum
from T0+0.003 to T0+47.489 s is best fit by
a Band function with Epeak = 239 +/- 5 keV,
alpha = -0.66 +/- 0.02, and beta = -2.42 +/- 0.06.

The event fluence (10-1000 keV) in this time interval is
(6.28 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+26 s in the 10-1000 keV band is 34.4 +/- 0.4 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/"