TITLE:   GCN CIRCULAR
NUMBER:  34670
SUBJECT: GRB 230911D: Fermi GBM observation
DATE:    23/09/11 22:45:14 GMT
FROM:    Lorenzo Scotton at UAH <lscottongcn@outlook.com>

L. Scotton (UAH), R. Hamburg (CNRS/IJCLab), and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 07:53:09.72 UT on 11 September 2023, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 230911D (trigger 716111594 / 230911329),
which was also detected by the Fermi LAT (F. Longo et al. 2023, GCN 34668) 
and Konus-Wind (D. Frederiks et al. 2023, GCN 34659).

The Fermi GBM Final Localization (GCN 34656) is consistent with the Fermi LAT position.

The angle from the Fermi LAT boresight at the GBM trigger time is 72 degrees.

The GBM light curve consists of multiple peaks
with a duration (T90) of about 45.6 s (50-300 keV).
The time-averaged spectrum from T0-4.4 s to T0+77.6 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -1.00 +/- 0.01 and
the cutoff energy, parameterized as Epeak, is 429.9 +/- 7.8 keV

The event fluence (10-1000 keV) in this time interval is 
(1.214 +/- 0.007)E-04 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+16.1 s in the 10-1000 keV band
is 24.8 +/- 0.3 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 420.6 +/- 9.0 keV, alpha = -1.00 +/- 0.01 and beta = -3.02 +/- 0.25.

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/"