GCN Circular 44500

S.Y.Fu (HUST), Y. L. Wang (NAO, CAS; ICE, CSIC), C.L.Guo (NAO, CAS), X. Tian (GXU), W. D. Zhang (NAO, CAS) on behalf of the Einstein Probe (EP) team:

The fast X-ray transient EP260507a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Fu et al., GCN 44488
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 ). The refined analysis of the WXT data shows that the event started at T0=2026-05-07T13:47:44.0 (UTC) and lasted for 15 s before the observation was interrupted by the autonomous follow-up observation (i.e. T90 > 15 s). The average 0.5–4 keV spectrum of WXT can be modeled with an absorbed power law, adopting a fixed Galactic hydrogen column density of 5.55 x 10^20 cm^-2 and an additional column density of 5.77 x 10^21 cm^-2. This additional absorption significantly improves the fit quality, yielding a photon index of 1.47 (+-0.79). The derived average unabsorbed 0.5-4 keV flux is 1.98 (-0.70/+2.20) x 10^(-8) erg/s/cm^2.
 
The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed at 2026-05-07T13:51:52 (UTC), about 4 minutes after T0. The exposure time of this observation is 5046 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 206.899, -22.2364 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 adopting a fixed Galactic equivalent hydrogen column density of 5.55 x 10^20 cm^-2 and an additional column density of 8.33 x 10^20 cm^-2，yielding a photon index of 2.10 (+-0.06). The derived average unabsorbed 0.3-10 keV flux is 1.82 (-0.07/+0.08) x 10^(-11) erg/s/cm^2. The uncertainties are at the 90% 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).