GCN Circular 44960
Subject
GRB 260616A: Fermi-LAT detection
Event
Date
2026-06-16T23:28:45Z (19 hours ago)
From
N. Di Lalla at Stanford University <niccolo.dilalla@stanford.edu>
Via
email
S. Lopez (CNRS / IN2P3), N. Di Lalla (Stanford University), R. Gupta (NASA/GSFC), F. Longo (University and INFN, Trieste), D. Depalo (Politecnico & INFN Bari), N. Omodei (Stanford University), and J. Valverde (Marquette University) report on behalf of the Fermi-LAT collaboration:
At 03:21:54 UT on 16 June 2026, Fermi-LAT detected high-energy emission from GRB 260616A, which was also detected by Fermi-GBM (trigger 803272919/ 260616140, GCN #44948).
The best LAT on-ground location is found to be
RA, Dec = 93.53, -32.07 (J2000)
with an error radius of 0.54 deg (90 % containment, statistical error only).
This was 111 deg from the LAT boresight at the time of the trigger.
The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the trigger with high significance. The photon flux above 100 MeV in the time interval 500 - 3000 s after the GBM trigger is (1.8 ± 0.6)E-6 ph/cm2/s. The estimated photon index above 100 MeV is -2.4 ± 0.4. The highest energy photon has an energy of 724 MeV and occurs at 1690 s after trigger time.
The Fermi-LAT point of contact for this burst is Samantha López (lpsamy18@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.