TITLE: GCN CIRCULAR NUMBER: 44277 SUBJECT: GRB 260411B: Fermi-LAT detection DATE: 26/04/12 16:41:28 GMT FROM: Rahul Gupta at NASA GSFC <rahul.gupta@nasa.gov> F. Longo (Univ. and INFN Trieste), D. Depalo (Politecnico and INFN Bari), R. Gupta (NASA/GSFC), A. Holzmann Airasca (UniTrento and INFN Bari), N. Omodei (Stanford University), and N. Di Lalla (Stanford University) report on behalf of the Fermi-LAT team: At 08:04.35.31 UT on April 11th, 2026, Fermi-LAT detected high-energy emission from GRB 260411B, which was also detected by Fermi-GBM (trigger 797587480/260411337, GCN #44262 and #44266), and SVOM (Wang et al. 2026, GCN #44268). An optical counterpart candidate was detected by GOTO (O'Neill et al. 2026, GCN #44265), DOT (Gupta et al. 2026, GCN #44271), Ondrejov D50 (Jeiinek et al. 2026, GCN #44272), and COLIBRI' (Sánchez Álvarez et al. 2026, GCN #44274). The GBM location was initially inside the LAT field of view at an angle of 60 degrees to the LAT boresight, and remained in the LAT field of view until ~T0+500 s. No significant excess is seen using standard >100 MeV likelihood analysis procedures. Using the LAT Low Energy (LLE) data selection, over 190 counts above background were detected within a 20 s interval coinciding with the time of the GBM emission. This data selection has insufficient spatial resolution to provide a reliable LAT localization. Since an excess of events was not seen using the standard analysis selection, this detection is likely due to low-energy gamma-rays (below 100 MeV). The Fermi-LAT point of contact for this burst is Sara Cutini (sara.cutini@pg.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. View this GCN Circular online at https://gcn.nasa.gov/circulars/44277. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...