TITLE: GCN CIRCULAR NUMBER: 40060 SUBJECT: GRB 250403A: Fermi GBM observations DATE: 25/04/04 16:31:50 GMT FROM: Peter Veres at University of Alabama in Huntsville veresp@gmail.com
P. Veres (UAH), M. Godwin (UAH), C. Meegan (UAH) and E. Bissaldi (Politecnico and INFN Bari) report on behalf of the Fermi GBM Team:
"At 15:15:22.83 UT on 03 April 2025, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 250403A (trigger 765386127 / 250403636). This GRB was also detected by the SVOM (Julakanti et al. 2025, GCN 40026). The Fermi GBM Final Real-time Localization (GCN 40025) is consistent with the SVOM position.
The angle from the Fermi LAT boresight at the GBM trigger time is 59 degrees.
The GBM light curve consists of multiple pulses with a duration (T90) of about 16.4 s (50-300 keV). The time-averaged spectrum from T0-4.1 s to T0+14.3 s is best fit by a simple power law function with index -1.65 +/- 0.02.
The event fluence (10-1000 keV) in this time interval is (6.7 +/- 0.2)E-6 erg/cm^2. The 1-sec peak photon flux measured starting from T0+3.3 s in the 10-1000 keV band is 4.2 +/- 0.2 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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