GCN Circular 34670

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
Not found
 
 
) 
and Konus-Wind (D. Frederiks et al. 2023, GCN 34659
Not found
 
 
).

The Fermi GBM Final Localization (GCN 34656
Not found
 
 
) 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/"