TITLE:   GCN CIRCULAR
NUMBER:  42340
SUBJECT: GRB 251011A: Fermi GBM Observation
DATE:    25/10/18 02:27:15 GMT
FROM:    rhamburg@usra.edu

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

"At 03:41:40.09 UT on 11 October 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 251011A (trigger 781846905/251011154), which was also
detected by AstroSat (Tembhurnikar et al. 2025, GCN 42199), Insight-HMXT (Wang 
et al. 2025, GCN 42210), and Swift-BAT/GUANO (DeLaunay et al. 2025, GCN 42245).
The Fermi GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight is 62 degrees.

The GBM light curve consists of a multi-peaked structure with a duration (T90)
of about 4.9 s (50-300 keV). The time-averaged spectrum from T0-0.7 to T0+4.9 s
is best fit by a power law function with an exponential high-energy cutoff.
The power law index is -0.76 +/- 0.01 and the cutoff energy, parameterized as 
Epeak, is 136 +/- 1 keV.

The event fluence (10-1000 keV) in this time interval is 
(3.26 +/- 0.07)E-06 ergs/cm^2 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1.8 s in the 10-1000 keV band is 11.5 +/- 0.3 ph/s/cm^2.

A Band function fits the spectrum equally well with Epeak = 125 +/- 1 keV, 
alpha = -0.69 +/- 0.01 and beta = -2.70 +/- 0.04.

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/"