GCN Circular 44912
Subject
EP260610b: refined analysis of the EP-WXT and follow-up EP-FXT observations
Event
Date
2026-06-11T12:50:17Z (2 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
C. L. Guo, H. Y. Ren, Z. X. Ling (NAO, CAS), H.Z. Wu (HUST, CAS) on behalf of the Einstein Probe (EP) team:
The fast X-ray transient EP260610b was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Wu et al., GCN 44895), and followed by several telescopes (Levan et al. GCN 44897, Xin et al. GCN 44900, Zhu et al. GCN 44902, Burkhonov et al. GCN 44904, Méndez et al. GCN 44906). The WXT observation started at T0=2026-06-10 12:44:25 (UTC), and lasted for around 230 s before being interrupted by autonomous follow-up. The WXT light curve shows an increase in flux during the last 30 s. The average WXT 0.5–4 keV spectrum can be fitted with an absorbed power-law model with a fixed Galactic hydrogen column density of 2.43 × 10^20 cm^−2 and a photon index of 1.48 (+0.81/−0.70). The derived average unabsorbed 0.5–4 keV flux is 2.39 (+1.35/−0.90) × 10^−10 erg s^−1 cm^−2.
The autonomous follow-up observation with the Follow-up X-ray Telescope (FXT) on board EP started at 2026-06-10 12:50:34 (UTC), about 370s after T0. The exposure time was approximately 3726s. The on-ground analysis of the FXT data detected an uncatalogued X-ray source at R.A. = 267.6268 deg, DEC = 46.5388 deg (J2000), with an uncertainty of 10 arcsec in radius (90% C.L., including statistical and systematic uncertainties). The average FXT 0.5–10 keV spectrum can be fitted with an absorbed power-law model with a fixed Galactic hydrogen column density of 2.43 × 10^20 cm^−2 and a photon index of 2.19 (+0.1/−0.1). The derived average unabsorbed 0.5–10 keV flux is 7.36 (+0.4/−0.4) × 10^−12 erg s^−1 cm^−2. The uncertainties quoted above are at the 90% confidence level.
Launched on January 9, 2024, EP is a space X-ray observatory designed 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).