TITLE:   GCN CIRCULAR
NUMBER:  45804
SUBJECT: EP261003a: J-band upper limit with WINTER
DATE:    26/10/03 13:29:38 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 EP261003a (Lao et al., GCN 45798) 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 2026-10-03 at 02:46:15.793 UTC in the J band (2.53 hr after the EP-WXT trigger), consisting of 29*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 any new source in the refined FXT localization (Lao et al., GCN 45803) in our stacked image.
We obtain the following 5-sigma upper limit: J = 19.43 mag (AB).

We also note deep upper limit by Globus et al., GCN 45801.

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.