TITLE: GCN CIRCULAR NUMBER: 40413 SUBJECT: GRB 250507A: J-band observations with WINTER DATE: 25/05/10 03:12:44 GMT FROM: Geoffrey Mo at MIT <gmo@mit.edu> Geoffrey Mo (MIT), Tomas Ahumada (Caltech), Benjamin Schneider (LAM), Viraj Karambelkar (Caltech), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of GRB 250507A (Wang et al., GCN 40374) in the near-infrared J-band with the Palomar 1-m telescope, equipped with the 1-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations were triggered automatically and began at 2025-05-09T05:54:11 UTC (1.97 days after the GRB), consisting of 15 x 120 s 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 any uncataloged sources in the SVOM/MXT (Wang et al., GCN 40374; Maggi et al., GCN 40381), EP-FXT (Zhang et al., GCN 40385), or Swift-XRT (Osborne et al., GCN 40389) localizations after visual comparison to archival PanSTARRS-1 (Chambers et al. 2016) y-band imaging. This is consistent with observations by Ducoin et al., GCN 40376; Xin et al., GCN 40379; Brivio et al., GCN 40380; and Zheng et al., GCN 40400. We obtain the following 5-sigma upper limit: J ~ 19.5 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/40413. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...