TITLE: GCN CIRCULAR NUMBER: 38018 SUBJECT: EP241026b: Liverpool Telescope optical follow-up DATE: 24/10/31 20:38:32 GMT FROM: A. Bochenek at Liverpool John Moores University a.m.bochenek@2023.ljmu.ac.uk

A. Bochenek and D. A. Perley (LJMU) report:

We observed the field of the fast X-ray transient EP241026b (Lian et al., GCN 37902) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 6x200s exposures the SDSS r filter starting at 2024-10-31 01:41:20 UT, approximately 4.31 days after the trigger.

The potential optical counterpart reported by Rossi et al. (GCN 37938) is marginally detected: forced photometry at the source location gives a 1.7-sigma detection, at a magnitude of r = 23.0 (-0.5, +0.9). More conservatively, a 2-sigma upper limit on the source magnitude is r > 22.1. Photometry was obtained using nearby PanSTARRS secondary standards and was not corrected for extinction.

The transient has therefore faded since the observation by Rossi et al. (GCN 37938) - comparing their detection to our upper limit, it has faded by at least 0.6 mag between 1.48 and 4.31 days post-trigger.

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