TITLE: GCN CIRCULAR NUMBER: 42204 SUBJECT: GRB 251011B: Fermi GBM Observation DATE: 25/10/12 00:26:55 GMT FROM: oindabimukherjee@gmail.com
O. Mukherjee (USRA), C. Meegan (UAH), U. Pathak (IIT Bombay) and L. Scotton (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 07:08:21.91 UT on 11 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251011B (trigger 781859306/251011297). which was also detected by Swift BAT (A. D'Ai et al. 2025, GCN 42197), and Swift XRT (P.A. Evans et al. 2025, GCN 42201). The Fermi GBM on-ground location is consistent with the Swift BAT position.
The angle from the Fermi LAT boresight is 81.8 degrees.
The GBM light curve consists of a single pulse with a duration (T90) of about 35 s (50-300 keV). The time-averaged spectrum from T0-8.0 to T0+26.5 s is best fit by a Band function with Epeak = 36 +/- 5 keV, alpha = 0.4 +/- 0.7, and beta = -2.2 +/- 0.1.
The event fluence (10-1000 keV) in this time interval is (3.3 +/- 0.3)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.58 s in the 10-1000 keV band is 3 +/- 0.2 ph/s/cm^2.
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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