GCN Circular 44016
Subject
EP260314a: refined analysis of the EP-WXT and EP-FXT observations
Event
Date
2026-03-15T09:29:55Z (2 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Yue Wu (NJU), Rui-Zhi Li (YNAO, CAS), Yaqi Zhao (USTC, PRIC) and Hai-Wu Pan (NAOC) on behalf of the Einstein Probe (EP) team:
The fast X-ray transient EP260314a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Zhao et al., GCN 44010). The transient was detected immediately when WXT observation started at T0=2026-03-14T22:51:20. The WXT observation lasted for approximately 16 seconds, and was interrupted due to the autonomous follow-up observation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a hydrogen column density of 0.54（-0.27/+0.32）×10^22 cm^-2 and a photon index of 1.81(-0.75/+0.83). The derived average unabsorbed 0.5-4 keV flux is 2.14 (-0.55/+1.13) × 10^(-8) erg/s/cm^2.
The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously at 2026-03-14T22:54:51 (UTC, T0+211 s). The exposure time of this observation is 2.9ks. On-ground analysis of the FXT data found an uncatalogued source at R.A., Dec. = 211.8426, -23.4577 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent with the WXT position. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 0.22 (-0.07/+0.07) × 10^22 cm^-2 and a photon index of 2.21 (-0.27/+0.28). The derived average unabsorbed 0.5-10 keV flux is 5.11 (+0.46/-0.41) × 10^(-12) erg/s/cm^2.
A follow-up observation with the EP/FXT was planned, and further information will be updated when the telemetry data is received.
The optical follow-up observations were performed by Li et al. (GCN 44009), Li et al. (GCN 44013), Lipunov et al. (GCN 44014) and Pérez-García et al. (GCN 44015). We note that the SVOM/VT candidate (Li et al., GCN 44013) is located within the 10 arcsec error circle of EP/FXT. Further multi-band follow-up observations are encouraged to explore the nature of EP260314a.
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).