GCN Circular 46168
Subject
EP261105a: refined analysis of the EP-WXT and follow-up EP-FXT observations
Event
Date
2026-11-06T08:33:37Z (12 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), and followed by several telescopes (Ma et al. GCN 46160, van Hoof et al. GCN 46162, Buckley et al. GCN 46165). The WXT observation started at T0=2026-11-05 10:03:24 (UTC), and lasted for around 270 s before being interrupted by autonomous follow-up. The WXT light curve shows an increase in flux from about T0+180 s, and starts to decreas from about T0+200 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 4.84 × 10^20 cm^−2 and a photon index of 0.92 (+0.83/−0.77). The derived average unabsorbed 0.5–4 keV flux is 2.58 (+1.75/−1.14) × 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 2026-11-05 10:10:39 (UTC), 435 s after T0. The exposure time was 4354 s. The on-ground analysis of the FXT data detected an uncatalogued X-ray source at R.A. = 91.0018 deg, DEC = -54.2637 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 4.84 × 10^20 cm^−2 and a photon index of 2.11 (+0.11/−0.11). The derived average unabsorbed 0.5–10 keV flux is 4.12 (+0.30/−0.28) × 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).