GCN Circular 45112
Subject
EP260707a (by EP-FXT): NOT optical upper limit
Event
Date
2026-07-08T04:41:03Z (6 days ago)
From
sqjiang at NAOC <sqjiang@bao.ac.cn>
Via
Web form
X. Liu, S.Q. Jiang, Z.P. Zhu, J. An, L.B. He, D. Xu (NAOC), S.Y. Fu (HUST), J.P.U. Fynbo (DAWN/NBI), F. Mustafaj (NOT) report:
We observed the field of the uncatalogued X-ray source detected by EP-FXT (Zhou et al., GCNs 45107 & 45111), located within the EP-WXT error circle of the very likely fake event of EP260707a, using the 2.56m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observation started at 2026-07-08 01:09:50.53 UT, i.e., 8.41 hr post-burst, and a series of r-band frames were obtained.
No new optical transient is detected in the stacked image within the EP-FXT error circle (GCN 45107), down to a 5-sigma limiting magnitude of r ~ 23.0 (AB), calibrated with Pan-STARRS DR2 stars in the field and not corrected for Galactic extinction.