GCN Circular 35369

E. Bissaldi (Politecnico and INFN Bari), P. Veres (UAH) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:


"At 09:47:17.81 UT on 15 December 2023, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 231215A (trigger 724326442 / 231215408),
which was also detected by the Swift/BAT (D'Avanzo et al. 2023, GCN 35343
Not found
 
 
).
The GBM on-ground location is consistent with the Swift position.
We note that the burst was automatically named incorrectly (GRB 231215B, GCN 35344
Not found
 
 
),
likely because the GBM trigger differs from the BAT trigger by 8 s.

The angle from the Fermi LAT boresight
at the GBM trigger time is 111 degrees.

The GBM light curve consists of a single bright pulse
with a duration (T90) of about 16 s (50-300 keV).
The time-averaged spectrum from T0-1.8 s to T0+32 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is 0.73 +/- 0.02 and
the cutoff energy, parameterized as Epeak, is 761 +/- 22 keV.

The event fluence (10-1000 keV) in this time interval is
(7.15 +/- 0.05)E-5 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+7.5 s in the 10-1000 keV band
is 20.3 +/- 0.4 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 759 +/- 23 keV, alpha = -0.73 +/- 0.02
and beta = 4.7 +/- 1.4.


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/"