GCN Circular 44908
Subject
EP260610a: refined analysis of the EP-WXT and follow-up EP-FXT observations
Event
Date
2026-06-11T08:52:18Z (2 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
H. Y. Ren, C. L. Guo, Z. X. Ling (NAO, CAS), H.Z. Wu (HUST, CAS), on behalf of the Einstein Probe (EP) team:
The fast X-ray transient EP260610a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission at 2026-06-10T04:41:46 (UTC). We note that the trigger time reported in Wu et al., GCN 44889 was incorrect. The correct trigger time is 2026-06-10T04:49:21 (UTC). The WXT light curve lasted for around 450 seconds before the interruption of the autonomous follow-up. 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 0.46 × 10^21 cm^−2 and a photon index of 0.89 (+0.60/−0.57). The derived average unabsorbed 0.5–4 keV flux is 2.71 (+1.21/−0.70) × 10^−10 erg s^−1 cm^−2.
The autonomous follow-up observation with the Follow-up X-ray Telescope (FXT) on board EP was performed at 2026-06-10T04:52:19 (UTC). The exposure time was approximately 3.5 ks. The on-ground analysis of the FXT data detected an uncatalogued X-ray source at R.A. = 306.1022 deg, DEC = −25.9045 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 0.46 × 10^21 cm^−2 and a photon index of 1.95 (+0.07/−0.07). The derived average unabsorbed 0.5–10 keV flux is 0.82 (+0.06/−0.05) × 10^−11 erg s^−1 cm^−2. The uncertainties quoted above are at the 90% confidence level.
We note that follow-up observations were carried out with COLIBRÍ (de Ugarte Postigo et al., GCN 44890) and SVOM/VT (Li et al., GCN 44896), but no optical counterpart was detected in these observations.
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).