TITLE: GCN CIRCULAR NUMBER: 39291 SUBJECT: GRB 250207A: Fermi GBM Observation DATE: 25/02/11 21:31:46 GMT FROM: oindabimukherjee@gmail.com

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

"At 01:16:03.15 UT on 07 February 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250207A (trigger 760583768/250207053). which was also detected by Swift BAT (Ferro et al. 2025, GCN 39182), COLIBRÍ/DDRAGO (Angulo et al. 2025, GCN 39186), Swift/UVOT (Kuin et al. 2025, GCN 39199), and Konus-Wind (Ridnaia. et al. 2025, GCN 39284) The Fermi GBM Final Real-time Localization (GCN 39181) is consistent with the Swift BAT position.

The angle from the Fermi LAT boresight is 46 degrees.

The GBM light curve consistes of a single emission episode with multiple peaks with a duration (T90) of about 20 s (50-300 keV). The time-averaged spectrum from T0-3.1 to T0+25.6 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.10 +/- 0.06 and the cutoff energy, parameterized as Epeak, is 290 +/- 30 keV.

The event fluence (10-1000 keV) in this time interval is (1.04 +/- 0.04)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+12 s in the 10-1000 keV band is 4.7 +/- 0.3 ph/s/cm^2.

A Band function fits the spectrum equally well with Epeak= 240 +/- 30 keV, alpha = -1.03 +/- 0.08 and beta = -2.3 +/- 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/"

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