GCN Circular 44436
Subject
EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations
Event
Date
2026-05-01T07:13:34Z (9 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. Wang (PMO, CAS; UCB), Y. L. Wang (NAO, CAS; ICE, CSIC), G. J. Yang, C.C Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team:
The X-ray transient EP260430a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Wang et al., GCN 44427) at 2026-04-30T02:32:47 (UTC). The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 0.3× 10^21 cm^-2, and a photon index of 0.84 (+0.19/-0.18). The derived average unabsorbed 0.5-4 keV flux is 4.63 (+2.54/-1.56) × 10^(-10) erg/s/cm^2.
Follow-up observation by the Follow-up X-ray Telescope (FXT) on board EP was performed at 2026-04-30T02:34:41 (UTC). The exposure time of the observation is around 3 ks. The on-ground analysis of the FXT data found an uncatalogued source at R.A. = 178.3355, DEC = -10.2146 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT light curve shows a raipd decay. The average FXT 0.5-10 keV spectra can be fitted with an absorbed power-law with a fixed Galactic hydrogen column density of 0.3× 10^21 cm^-2, and a photon index of 4.61 (+/-0.20). The derived average unabsorbed 0.5-10 keV flux is 1.27 (-0.16/+0.17) × 10^(-11) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
We note that follow-up observations were carried out by Lipunov et al. (GCN 44428), Fortin et al. (GCN 44431) and Chácon et al. (GCN 44432), but no optical counterpart was detected in these observation.
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).