TITLE:   GCN CIRCULAR
NUMBER:  43647
SUBJECT: GRB 260208B: Fermi-LAT detection
DATE:    26/02/08 16:31:58 GMT
FROM:    A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca@unitn.it>

F. Longo (University and INFN, Trieste), D. Depalo (Politecnico and INFN Bari), A. Holzmann Airasca (UniTrento and INFN Bari) and R. Gupta (NASA/GSFC) report on behalf of the Fermi-LAT team:

At 09:52:44.91 UT on February 8th, 2026 Fermi-LAT detected high-energy emission from GRB 260208B, which was also detected by Fermi-GBM (trigger 792237169 / 260208412, GCN #43638).

The best LAT on-ground location is found to be
RA, Dec = 99.64, -13.84 (J2000)
with an error radius of 0.06 deg (90 % containment, statistical error only).

This was 13 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 0 - 2 ks after the GBM trigger is (8.7 ± 1.2)E-6 ph/cm2/s. The estimated photon index above 100 MeV is -2.03 ± 0.12. The highest energy photon has an energy of 31 GeV and occurs at 815 s after trigger time.

A Swift ToO request has been approved for this burst.

The Fermi-LAT point of contact for this burst is Chiara Bartolini (chiara.bartolini@ba.infn.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.