TITLE: GCN CIRCULAR NUMBER: 40404 SUBJECT: EP250508a: Liverpool Telescope optical upper limits DATE: 25/05/09 09:01:45 GMT FROM: Rob Eyles-Ferris at U of Leicester raje1@leicester.ac.uk
R. A. J. Eyles-Ferris, P. T. O’Brien and R. L. C. Starling (U of Leicester) report:
We observed the field of the X-ray transient EP250508a (Liang et al., GCN 40390; Zhao et al., GCN 40399; Liang et al., GCN 40403) with the 2m Liverpool Telescope using the IO:O instrument. We obtained 6x150s exposures in the SDSS r’ filter starting at 2025-05-08 21:07:19 UT and 6x150s exposures in the SDSS z’ filter starting at 2025-05-08 21:24:25 UT, approximately 15.1 hours after the X-ray detection.
We performed image subtraction on the stacked images using reference images from Pan-STARRS and also compared the stacked and reference images manually. Consistent with Ugarte Postigo et al. (GCN 40391), Lipunov et al. (GCN 40393), Brivio et al. (GCN 40395) and Zheng et al. (GCN 40401), we identify no new sources within the error region of the EP/FXT source.
At the position of the optical counterpart candidate identified by Xin et al. (GCN 40402), we derive 3-sigma upper limits of r’ > 21.5 and z’ > 21.5 with photometry calibrated to Pan-STARRS and not corrected for Galactic extinction.
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