GCN 43842: EP260224a: LCO optical upper limits

2026-02-26T12:00:50.891Z | rev 0 | event: EP260224a
R. A. J. Eyles-Ferris (Leicester), A. van Hoof (Radboud), A. Martin-Carrillo (UCD), P. G. Jonker (Radboud), and A. J. Levan (Radboud) report on behalf of a larger collaboration:

We observed the field of the fast X-ray transient EP260224a (Yang  et al., GCN 43828) using LCO 1m telescopes located at the Cerro Tololo Inter-American Observatory (Chile) and the South African Astronomical Observatory (South Africa) equipped with the SINISTRO instrument. A series of 6x300 s exposures were taken in each of the SDSS-r and SDSS-z filters, starting at 2026-02-26 03:25:00 UT (32.4 hr after the trigger) and 2026-02-25 23:23:55 UT (30.3 hr after the trigger) respectively.

We performed subtractions on our stacked images using a template image from the KMTNet Synoptic Survey of the Southern Sky (Kim et al. 2016, doi:10.5303/JKAS.2016.49.1.37) and compared the stacks and template manually. No new source is detected within or at the border of the EP/WXT uncertainty region (Yang et al., GCN 43828). From the stacked images, we obtain the following 3-sigma upper limits: 

r > 23.6
z > 21.6

These upper limits are in AB magnitudes, calibrated using nearby stars from the SkyMapper catalog, and are not corrected for Galactic extinction.