TITLE: GCN CIRCULAR NUMBER: 39367 SUBJECT: GRB 250217C: Fermi GBM Observation DATE: 25/02/18 18:55:40 GMT FROM: Jacob Smith at Fermi-GBM Team jrs0118@uah.edu

Jacob Smith (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:

At 23:54:41.80 UT on 17 February 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250217C (trigger 761529286/250217996). which was also detected by AstroSat (M. Tembhurnikar, et al. 2025, GCN 39359) and IPN triangulation (A.S. Kozyrev, et al. 2025, GCN 39365). The Fermi GBM on-ground location is consistent with the IPN triangulation.

The angle from the Fermi LAT boresight is 100 degrees.

The GBM light curve consists of a double emission episode with a duration (T90) of about 0.35 s (50-300 keV). The time-averaged spectrum from T0-0.06 to T0+0.38 s is best fit by a Band function with Epeak = 85 +/- 13 keV, alpha = -0.2 +/- 0.3, and beta = -1.83 +/- 0.04.

The event fluence (10-1000 keV) in this time interval is (1.68 +/- 0.05)E-06 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.0 s in the 10-1000 keV band is 62 +/- 3 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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