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/"
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