Einstein Probe detection of a likely new X-ray transient

ATel #17964; G. L. Huang (IHEP), A. Li (BNU), C. Y. Wang (THU), W. D. Zhang (NAOC) on behalf of the Einstein Probe team
on 13 Aug 2026; 14:49 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Yuan Liu (liuyuan@bao.ac.cn)

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We report the detection of a new X-ray transient by the Wide-field X-ray Telescope (WXT) onboard the Einstein Probe (EP), designated EP260812c. EP-WXT first detected the current outburst at 2026-08-12T20:10:43 (UTC), with a flux of about 7.43×10^-11 erg/cm^2/s, located at (R.A., DEC) = (267.4863 deg, -32.7155 deg) and (Galactic I, b) = (357.243 deg, -2.747 deg), with a 90% positional uncertainty radius of 2.2 arcmin. A simple absorbed power-law model yielded a photon index of approximately 1.5 (-1.5/+1.7) and an absorption column density of 1.2 (-1.0/+1.4) x10^22 (90% C.L. statistical and systematic). We note that an X-ray nova was newly detected by MAXI at a position 12.6 arc-minutes away (Atel #17963, Negoro et al. 2026). Given the positional uncertainty of MAXI/GSC , we consider the EP-WXT and MAXI detections to be the same source. We also note that within the WXT error circle there is an X-ray source 1eRASS J175013.2-324130. Further observations are needed to pin down the source position so as to confirm whether the X-ray outburst detected by EP and MAXI is associated with 1eRASS J175013.2-324130.

The source was further detected in later WXT observations as follows, indicating that the source is still brightening.

UTC flux [x10^-11 erg/cm^2/s]

2026-08-13T03:08:53 29.7

2026-08-13T04:10:58 58.0

2026-08-13T10:32:58 129.0

Follow-up observations by EP-FXT have been scheduled. Multi-wavelength follow-up observations are encouraged to identify the nature of this likely new X-ray transient.

Launched on January 9, 2024, EP is a space X-ray observatory designed to monitor the soft X-ray sky with rapid X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE, and CNES.

MAXI/GSC detection of a new X-ray nova MAXI J1750-327