Einstein Probe detection of an X-ray transient EP260617a

ATel #17848; S. Q. Jiang (NAO, CAS), J. Yang (ZZU), H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team
on 18 Jun 2026; 12:18 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Yuan Liu (liuyuan@bao.ac.cn)

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We report on the discovery of an X-ray transient, designated EP260617a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission through the ground data analysis. The source was detected in one WXT observation starting at (UTC) 02:01:04 on 2026 June 17. No significant variability was detected during the 1.5 ks exposure. The position of the transient is R.A. = 209.016 deg, Dec. = -1.611 deg (J2000), with an uncertainty radius of 2.5 arcmin (90% confidence level, including both statistical and systematic uncertainties). There is no historical X-ray source in the WXT error circle.

The WXT spectrum can be fitted with an absorbed power-law model. With the fixed Galactic hydrogen column density of 4.3^20 cm^-2, we derived a photon index of 1.60 +/- 0.42. The unabsorbed 0.5-4 keV flux is (5.12 +/- 0.18) x 10^(-11) erg cm^-2 s^-1.

The follow-up observation with the Follow-up X-ray Telescope onboard EP is scheduled.

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).