TITLE: GCN CIRCULAR NUMBER: 43607 SUBJECT: GRB 250131A: FTW optical and NIR observations DATE: 26/02/02 22:00:00 GMT FROM: Ziyuan.Zhu@campus.lmu.de Ziyuan Zhu (LMU), Malte Busmann (LMU), Julius Gassert (LMU), Xander J. Hall (CMU), Brendan O’Connor (CMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report: We observed the counterpart of GRB 260131A (Fermi/GBM Team, GCN 43579; Frederiks et al., GCN 43590; Luo et al., GCN 43591; Li et al., GCN 43605) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i, and J bands for 15x 120s, starting at 2026-02-01T22:14:35 UT, (1.65 days after the trigger). We detect the counterpart in all bands and measure an r-band magnitude of r = 19.18 +/- 0.03 AB mag The magnitude is calibrated against the PS1 catalog and not corrected for Galactic extinction. We thank Christoph Ries from the Wendelstein Observatory for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/43607. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...