TITLE: GCN CIRCULAR NUMBER: 40836 SUBJECT: GRB 250625A: Fermi-LAT detection DATE: 25/06/26 08:10:58 GMT FROM: Davide Depalo at Politecnico and INFN Bari davide.depalo@ba.infn.it
N. Di Lalla (Stanford Univ.), A. Holzmann Airasca (UniTrento and INFN Bari), R. Gupta (NASA GSFC), and D. Depalo (Politecnico and INFN Bari) report on behalf of the Fermi-LAT Collaboration:
On June 25, 2025, Fermi-LAT detected high-energy emission from GRB 250625A, which was also detected by Fermi-GBM (trigger 772560301 / 250625670, GCN 40824), Swift-BAT/XRT (GCN 40825) and SVOM/VT (GCN 40830).
The best LAT on-ground location is found to be:
RA, Dec = 261.2, 22.4 (J2000)
with an error radius of 0.6 deg (90 % containment, statistical error only). This was 32 deg from the LAT boresight at the time of the GBM trigger (T0 = 16:04:57.51 UT).
The data from the Fermi-LAT shows a significant increase in the event rate that is spatially and temporally correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0 - 100 s after the GBM trigger is (1.12 ± 0.48) E-5 ph/cm2/s. The estimated photon index above 100 MeV is -2.00 ± 0.38.
The highest-energy photon is a 580 MeV event which is observed ~ 27 seconds after the GBM trigger.
The Fermi-LAT point of contact for this burst is Davide Depalo (d.depalo2@phd.poliba.it).
The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.
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