TITLE: GCN CIRCULAR NUMBER: 45519 SUBJECT: GRB 260903A: J-band upper limit with WINTER DATE: 26/09/04 20:05:20 GMT FROM: tanishk.mohan@iitb.ac.in Tanishk Mohan (IITB), Geoffrey Mo (Caltech/Carnegie), Viraj Karambelkar (Columbia), Benjamin Schneider (LAM), Tomas Ahumada (NOIRLab), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 260903A (Brunet et al., GCN 45499 and GCN 45517) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations began on 2026-09-04 at 05:43:17.936 UTC in the J band (17.1 hr after the SVOM/ECLAIRs trigger), consisting of 15*120 sec exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565). We do not detect the source at the optical counterpart position (Li et al., GCN 45504; Saccardi et al., GCN 45505; Malesani et al., GCN 45508; Russeil et al., GCN 45509; Moskvitin el al., GCN 45515; Bochenek et al., GCN 45516) in our stacked image. We obtain the following 5-sigma upper limit: J = 19.07 mag (AB). WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/45519. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...