GCN Circular 46204
Subject
EP261105a: Second EP-FXT follow-up observation
Event
Date
2026-11-09T09:48:38Z (3 hours ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
C. L. Guo, B. B. Zhang, Q.Y. Wu, W.D. Zhang (NAO, CAS), Y. Q. Zhao(PRIC, USTC)
on behalf of the Einstein Probe (EP) team:
The fast X-ray transient EP261105a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Guo et al., GCN 46155). A refined analysis of the EP-WXT and autonomous EP-FXT observations was subsequently reported by Guo et al. (GCN 46168). Optical and near-infrared follow-up observations were reported by Ma et al. (GCN 46160), van Hoof et al. (GCN 46162), Buckley et al. (GCN 46165), Waseem et al. (GCN 46170), Passaleva et al. (GCN 46172), and Waseem et al. (GCN 46191).
The EP-FXT performed a second follow-up observation of EP261105a beginning at 2026-11-06 03:27:37 (UTC), with an exposure of about 5363 s. The on-ground analysis of the FXT data detected an uncatalogued X-ray source at R.A. = 91.0002 deg, DEC = -54.2620 deg (J2000), with an uncertainty of 10 arcsec in radius (90% C.L., including statistical and systematic uncertainties), consistent with the X-ray source reported before by Guo et al. (GCN 46168). 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 4.84 × 10^20 cm^−2 and a photon index of 2.05(+1.79/-1.11). The derived average unabsorbed 0.5–10 keV flux is 5.31 (+6.48/-2.75) × 10^−14 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).