EP260530a/AT2026nwl: refined analysis of the EP-FXT observation

ATel #17825; W. F. Wen (SZTU), C. Y. Dai (NJU), Q. Y. Wu, H. Sun (NAO, CAS)
on 1 Jun 2026; 08:50 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Yuan Liu (liuyuan@bao.ac.cn)

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Following the detection of the X-ray transient EP260530a (Wu et al., ATel 17824), we performed a follow-up observation with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe mission. The observations began at 2026-05-31T05:53:39, about 22 hours after the EP-WXT detection. The exposure time is 2.5 ks. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 186.1046 deg, DEC = 28.7857 deg, with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic), which is 3 arcsec away from the position of the optical counterpart AT2026nwl. The spectrum can be fitted with a power-law plus a blackbody with a free NH. The best-fit results yield a photon index Gamma=1.3+/-0.3, the temperature kT = 0.054 +/-0.001keV and NH<2.8e20 cm-2. The derived unabsorbed flux in the 0.3-10 keV band is 5.3(-0.8, +0.9)E-11 erg/s/cm2 (90% C.L.).

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).