TITLE: GCN CIRCULAR NUMBER: 39502 SUBJECT: GRB 250225B: Fermi GBM Observation DATE: 25/02/26 22:38:04 GMT FROM: Matt Godwin msg0028@uah.edu
M. Godwin (UAH), C. Meegan (UAH), P. Veres (UAH) and R. Hamburg (USRA) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 19:39:13.83 UT on 25 February 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250225B (trigger 762205158/250225819). which was also detected by Swift BAT (H. A. Krimm et al. 2025, GCN 39473), Konus-Wind (A. Tsvetkova et al. 2025, GCN 39498), and VLT/FORS2 (Schneider et al. 2025, GCN 39494) The Fermi GBM on-ground location is consistent with the Swift BAT position.
The angle from the Fermi LAT boresight is 55 degrees.
The GBM light curve consists of one bright peak followed my multiple short peaks with a duration (T90) of about 335 s. The time-averaged spectrum from T0-3.6 to T0+340.5 s is best fit by a power law function with an exponential high-energy cutoff.The power law index is -1.30 +/- 0.05 and the cutoff energy, parameterized as Epeak, is 218 +/- 28 keV.
The event fluence (10-1000 keV) in this time interval is (2.14 +/- 0.11)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1.3 s in the 10-1000 keV band is 21.9 +/- 0.3 ph/s/cm^2.
The time-averaged spectrum of the first peak from T0 to T0+3.6 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.06 +/- 0.02 and the cutoff energy, parameterized as Epeak, is 568 +/- 42 keV. The Band function fits the spectrum equally well, with an Epeak of 547 +/- 46 keV, alpha = -1.05 +/- 0.03 and beta = -2.85 +/-0.67.
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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