TITLE:   GCN CIRCULAR
NUMBER:  45373
SUBJECT: EP260812a: refined analysis of the EP-WXT and autonomous EP-FXT observation
DATE:    26/08/13 11:10:34 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

G. J. Yang, H. R. Ren, Tian-Yu Liu and H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team:

The X-ray transient EP260812a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Liu et al., GCN 45362) and followed by Yin et al., GCN 45372. The refined analysis of the WXT data shows that the event started at T0=2026-08-12T11:20:03(UTC) and lasted for 60 s before the observation was interrupted by the autonomous follow-up observation.The average WXT 0.5–4 keV spectrum can be fitted with an absorbed power-law model. The best-fit photon index is 1.54 (-0.82/+0.88), and the hydrogen column density is 3.3 (-2.6/+2.9) × 10^21 cm^-2. The derived average unabsorbed 0.5–4 keV flux is 2.72 (-0.73/+1.59) × 10^-9 erg s^-1 cm^-2.

The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed at 2026-08-12 11:25:03(UTC), about 5 minutes after T0. The exposure time of this observation is 3898 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 311.4373, 14.1577 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic).  The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fitted Galactic equivalent hydrogen column density of 1.0 × 10^21 cm^-2 and a photon index of 2.00 (-0.08/+0.08). The derived average unabsorbed 0.5-10 keV flux is 2.61(-0.14/+0.15)× 10^(-11) erg/s/cm^2. The uncertainties are at the 1 sigma confidence level for the above parameters.

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).