TITLE: GCN CIRCULAR NUMBER: 44804 SUBJECT: EP260601a/GRB 260601B: EP-FXT follow-up observation DATE: 26/06/03 14:11:07 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> G. J. Yang (NAO, CAS), Z. X. Li, G. L. Huang, J. Y. Cao (IHEP, CAS), Y. Wang (PMO, CAS; UCB), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of the fast X-ray transient EP260601a (detected by EP-WXT, GCN 44766; followed by Liu et al., GCN 44764, Guelfand et al., GCN 44765, Li et al., GCN 44769, Mo et al., GCN 44777 and Liu et al., GCN 44789). This event is also temporally consistent with GRB 260601B reported by GECAM-B (Yu et al., GCN 44767, Wang et al., GCN 44768), NuSTAR (Waratkar et al., GCN 44771), CALET (Sugita et al., GCN 44773) and Insight-HXMT (Wang et al., GCN 44785). The observation started at 2026-06-03 01:13:47 UTC, about 30 hours after the WXT trigger, with an exposure time of 3.5 ks. The FXT telemetry data show that an uncatalogued source was detected within the WXT error circle at R.A. = 257.6584, DEC = -1.6447 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT X-ray spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 9 x 10^20 cm^-2. The best-fit photon index is 1.31 (-0.28/+0.29). The unabsorbed 0.5-10 keV flux is 9.2 (-2.2/+3.2) x 10^-13 erg cm^-2 s^-1. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/44804. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...