TITLE: GCN CIRCULAR NUMBER: 39030 SUBJECT: GRB 250119C: Fermi GBM Observation DATE: 25/01/25 14:45:44 GMT FROM: Jacob Smith at Fermi-GBM Team jrs0118@uah.edu

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

At 22:41:06.30 UT on 19 January 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250119C (trigger 759019271/250119945). which was also detected by Swift/BAT-GUANO (Ronchini, S. et al. 2025, GCN 39008). The Fermi GBM on-ground location is consistent with the Swift/BAT-GUANO position.

The angle from the Fermi LAT boresight is 66 degrees.

The GBM light curve consists of a single short emission episode with a duration (T90) of about 1 s (50-300 keV). The time-averaged spectrum from T0-0.2 to T0+0.2 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.63 +/- 0.2 and the cutoff energy, parameterized as Epeak, is 1120 +/- 420 keV.

The event fluence (10-1000 keV) in this time interval is (5.4 +/- 0.4)E-07 erg/cm^2. The 64-ms peak photon flux measured starting from T0-0.064 s in the 10-1000 keV band is 4.9 +/- 0.7 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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