TITLE: GCN CIRCULAR NUMBER: 39050 SUBJECT: GRB 250117A: Fermi GBM Observation DATE: 25/01/28 00:30:20 GMT FROM: oindabimukherjee@gmail.com
O. Mukherjee (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 20:21:57.89 UT on 17 January 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250117A (trigger 758838122/250117849). which was also detected by Konus-Wind (Ridnaia et al. 2025, GCN 39001), Swift/BAT-GUANO (DeLaunay et al. 2025, GCN 38988), and SVOM/GRM (Wang et al. 2025, GCN 38994).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 252.55, Dec = -26.18 (J2000 degrees, equivalent to J2000 20h 26m, +21d 13'), with a statistical uncertainty of 3.32 degrees. (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a mixture of two Gaussians, one with a radius of 1.8 degrees (52% contribution) and one with a radius of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]).
The angle from the Fermi LAT boresight is 67 degrees.
An overwhelming volume of data produced by a contemporaneous solar flare affected the spacecraft's ability to record data nominally, so TTE data was unavailable for this burst. Consequently, the temporal and spectral analysis used the CTIME and CSPEC data types only. The GBM light curve consists of one peak with a duration (T90) of about 0.8 s (50-300 keV). The time-averaged spectrum from T0+0.002 to T0+1.824 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.18 +/- 0.09 and the cutoff energy, parameterized as Epeak, is 904 +/- 386 keV.
The event fluence (10-1000 keV) in this time interval is (1.35 +/- 0.08)E-06 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.35 s in the 10-1000 keV band is 27 +/- 1 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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