EP260711a

Y.Wu (NJU), G. Y. Zhao (SYSU), Z.-Y. Jian (THU), and H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team:

We performed a follow-up observation of EP260711a (GCN 45139
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 ) with EP-FXT. The observation started at 2026-07-12 07:29:45 (UTC), about 22 hr after the EP-WXT detection, with a total exposure time of around 4.4 ks. No bright X-ray source was found in one FXT module observation. A weak uncatalogued source, with SNR of 3.2, was found within the WXT error circle after stacking the FXT A and FXT B data. The position of the source is at R.A., Dec. = 213.2229, -58.8956 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The average unabsorbed flux is around 3 x 10^(-14) erg/s/cm^2 in the 0.5-10 keV energy band. It is still unclear if the FXT detection is associated with EP260711a.

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).

Y.Wu (NJU), G. Y. Zhao (SYSU), H. W. Peng (THU), and H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team:

We report on the detection of a fast X-ray transient, designated EP260711a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission . The transient was identified in the telemetry data. The transient started at 2026-07-11T09:19:04 (UTC) and lasted for about 75s, with a peak flux of ~ 1.52 x 10^(-9) erg cm^-2 s^-1 in 0.5-4 keV. The position of the transient is R.A. = 213.2511 deg, Dec. = -58.8603 deg (J2000), with an uncertainty radius of 2.85 arcmin in radius (90% confidence level, including both statistical and systematic uncertainties). There are no known X-ray sources in the WXT error circle.

The average WXT 0.5-4 keV spectrum can be fitted by an absorbed power-law model with a fixed Galactic hydrogen column density of 1.30 (-0.58/+2.27) ×10^22 cm^-2 and a photon index of 2.49 (-1.29/+1.59). The derived average unabsorbed 0.5-4 keV flux is 2.31 (-1.18/+7.48) x 10^(-10) erg cm^-2 s^-1. The uncertainties are at the 90% confidence level for the above parameters.

Follow-up observations by EP-FXT will be arranged.

Launched on 2024 January 9, Einstein Probe is a space-based X-ray observatory designed to monitor the dynamic X-ray sky and perform rapid follow-up observations of newly discovered transients (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).