TITLE:   GCN CIRCULAR
NUMBER:  44467
SUBJECT: GRB 260504B: EP-FXT upper limit
DATE:    26/05/05 04:30:12 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

H. Zhou (PMO, CAS), Y.Q. Zhao (PRIC, USTC), T.Y. Liu, Y. Liu (NAOC, CAS) on behalf of the Einstein Probe (EP) team:

The Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission observed GRB 260504B (Saccardi, GCN 44454) autonomously at 2026-05-04 11:46:16 (UTC, ~ 2.25 hours after the burst). The exposure time of this observation is 1472s. On-ground analysis of the FXT data did not found any significant source within the error circle (90% C.L. radius of 167 arcsec) of GRB 260504B. The 5-sigma upper limit of EP-FXT observation is 4.8 x 10^-13 erg/s/cm^2 in the 0.5-10 keV band.

Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).