GCN Circular 41019
Subject
GRB 250706B/C: Fermi-LAT detection
Event
Date
2025-07-07T20:48:10Z (a year ago)
From
N. Di Lalla at Stanford University <niccolo.dilalla@stanford.edu>
Via
email
F. Longo (University and INFN, Trieste), N. Di Lalla (Stanford Univ.), A. Holzmann Airasca (UniTrento and INFN Bari), E. Bissaldi (Politecnico and INFN Bari), R. Gupta (NASA/GSFC), S. Lopez (CNRS / IN2P3) and J. Racusin (NASA/GSFC) report on behalf of the Fermi-LAT Collaboration:
On July 06, 2025, Fermi-LAT detected high-energy emission from GRB 250706B/C, which was also detected by Konus-Wind (named GRB 250706C in GCN 41013), SVOM/Eclairs (named GRB 250706B in GCN 40989), Swift/XRT (named GRB 250706B in GCN 40996) and Swift/UVOT (named GRB 250706B in GCN 41015).
The best LAT on-ground location is found to be:
RA, Dec = 41.17, -50.04 (J2000)
with an error radius of 0.07 deg (90 % containment, statistical error only). This was 87 deg from the LAT boresight at the time of the Konus-Wind trigger (T0 = 16:45:22.626 UT).
The data from the Fermi-LAT shows a significant increase in the event rate starting about 600 s after the Konus-Wind trigger, as soon as the GRB position entered the LAT field of view. The LAT emission is spatially and temporally correlated with both the Konus-Wind (GRB 250706C) and SVOM (GRB 250706B) emission with high significance, which are therefore to be considered part of the same burst. The photon flux above 100 MeV in the time interval 600 - 10000 s after the Konus-Wind trigger is (3.52 ± 0.59) E-6 ph/cm2/s. The estimated photon index above 100 MeV is -1.87 ± 0.12. The highest-energy photon is a 21 GeV event which is observed ~ 8 ks seconds after the Konus-Wind trigger.
The Fermi-LAT point of contact for this burst is Dimakatso Maheso (d.j.maheso@gmail.com).
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.