TITLE: GCN CIRCULAR NUMBER: 39726 SUBJECT: GRB 250313A: Fermi GBM Detection DATE: 25/03/15 02:17:47 GMT FROM: eliza.neights@gmail.com
Eliza Neights (George Washington University, NASA Goddard Space Flight Center), M. Godwin (UAH), C. Meegan (UAH) and O.J. Roberts (USRA) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 14:34:33.69 UT on 13 March 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250313A (trigger 763569278/250313607), which was also detected by Fermi LAT (Di Lalla et al. 2025, GCN 39711), AstroSat CZTI (Dasgupta et al. 2025, GCN 39714), SVOM/GRM (Wang et al. 2025, GCN 39716), and Konus-Wind (Frederiks et al. 2025, GCN 39721).
The Fermi GBM Final Position location is consistent with the Fermi LAT position.
The angle from the Fermi LAT boresight is 4 degrees.
The GBM light curve consists of two emission episodes, a bright pulse lasting 12 s after the trigger time and a dimmer pulse about 280 s later. The duration (T90) is about 295.2 s (50-300 keV). The time-averaged spectrum from T0-2.2 to T0+389.0 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.36 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 320 +/- 20 keV.
The event fluence (10-1000 keV) in this time interval is (9.4 +/- 0.1)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+4.7 s in the 10-1000 keV band is 55.4 +/- 0.5 ph/s/cm^2.
The spectrum is fit about equally well by a Band function with Epeak = 280 +/- 20 keV, alpha = -1.34 +/- 0.02, and beta = -2.23 +/- 0.13.
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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