TITLE:   GCN CIRCULAR
NUMBER:  36949
SUBJECT: GRB 240727B: Fermi GBM Observation
DATE:    24/07/27 19:00:39 GMT
FROM:    Cori Fletcher at USRA <cfletcher@usra.edu>

C. Fletcher (USRA), R. Hamburg (CNRS/IJCLab) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 06:00:08.96 UT on 27 July 2024, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 240727B (trigger 743752813/240727250).
which was also detected by Swift/BAT-GUANO (Ronchini et al. 2024, GCN 36945) and AstroSat (Waratkar et al. 2024, GCN 36943).
The Fermi GBM on-ground location is consistent with the Swift/BAT-GUANO position.

The angle from the Fermi LAT boresight is 114 degrees.

The GBM light curve consists of multiple peaks with a duration (T90)
of about 19 s (50-300 keV). The time-averaged spectrum
from T0-3.3 to T0+20.2 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.3 +/- 0.1 and the cutoff energy,
parameterized as Epeak, is 850 +/- 90 keV.

The event fluence (10-1000 keV) in this time interval is
(1.52 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+8.7 s in the 10-1000 keV band is 3.4 +/- 0.4 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 848 +/- 116 keV, alpha = -0.3 +/- 0.1 and beta = -2.5 +/- 0.3.

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/"