GCN Circular 45660
Subject
EP260920a: NOT early time optical upper limits
Event
Date
2026-09-20T16:14:12Z (a day ago)
From
Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>
Via
Web form
G. Corcoran (UCD), R. A. J. Eyles-Ferris (Leicester), P. G. Jonker (Radboud), J. N. D. van Dalen (Radboud), T. Pursimo (NOT, Aarhus University), A. Krzyzaniak (NOT) report on behalf of a larger collaboration:
We observed the field of the fast X-ray transient EP260920a (Ni et al., GCN 45649; Ni et al., GCN 45659) using the ALFOSC camera on the Nordic Optical Telescope (NOT) in rapid response mode (RRM). Observations consisted of a sequence of 5 x 180 s exposures in SDSS r-band followed by 9 x 150 s exposures in SDSS z-band. Observations started at 2026-09-20 00:19:12 UT (~18.3 minutes after the refined EP/WXT trigger time (Ni et al., GCN 45659)).
Within the refined EP-FXT position we identify no new sources down to the following limits:
r > 23.5 (Mid time 2026-09-20 00:27:36 UT, ~26.7 minutes after the refined start time)
z >22.6 (Mid time 2026-09-20 00:50:53 UT, ~50.0 minutes after the refined start time)
Our photometry was calibrated using nearby stars in the PanSTARRS catalog and is not corrected for Galactic extinction. Our non-detection is consistent with the later observations of Dornic et al. (GCN 45654), Li et al. (GCN 45657) and Zhu et al. (GCN 45659). We detect the candidate proposed by Liu et al. (GCN 45650) in both bands at magnitudes consistent with those catalogued in the Legacy Survey DR11 implying it is not the counterpart in agreement with Liu et al. (GCN 45653).