TITLE: GCN CIRCULAR NUMBER: 44506 SUBJECT: GRB 260509A: LCO optical counterpart detection DATE: 26/05/10 01:00:45 GMT FROM: SVOM_group <svomgroup@bao.ac.cn> A. Saccardi (CEA/Irfu), C. Wu (NAOC), D. Adrien (CEA/Irfu), L. Zhang (IHEP), Y. H. Cheng (YNU), report on behalf of the SVOM mission team: We observed the field of GRB 260509A detected by SVOM (Götz et al., GCN 44504) with the LCO 1m telescope at Cerro Tololo Observatory equipped with the Sinistro instrument. Our observation started on 2026-05-09 at 23:41:26 UT (about 1.84 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. The optical candidate reported by O'Neill et al. (GCN 44505) is clearly detected in our images. We measure the following magnitudes calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction: r = 19.79 +/- 0.05 AB (mid-time 1.92 hr after the trigger); z = 19.76 +/- 0.15 AB (mid-time 2.65 hr after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/44506. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...