GCN Circular 45861
EP261007b: J-band upper limit with WINTER
From: unknown
Issued: 2026-10-08 13:48 UTC
Type: X-ray Transient

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 EP261007b (Wen et al., GCN 45847) 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 2026-10-08 at 02:38:26.332 UTC in the J band (11.55 hr after the WXT trigger), consisting of 30*120 sec exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (GitHub - winter-telescope/mirar: Modular Image Reduction and Analysis Resource (MIRAR) (github.com), winter-telescope/mirar: v0.17.0 (doi.org)).

We do not detect any new source in the FXT localization and obtain the following 5-sigma upper limit: J = 19.6 mag (AB).
We also note early optical upper limits by Ma et. al., GCN 45849.

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.

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