GCN Circular 41627
Subject
EP250901a: Einstein Probe detection of an X-ray transient
Event
Date
2025-09-01T13:43:28Z (a month ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Y. J. Song, T. Zhao, J. W. Hu, C. L. Guo, Z. X. Ling (NAO, CAS), on behalf of the Einstein Probe (EP) team:
We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP250901a. The transient triggered EP-WXT (ID: 00109201113) at 2025-09-01T12:05:03 (UTC). The WXT position of the source is R.A. = 273.025 deg, DEC = 18.676 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The estimated WXT flux is around 4e-10 erg/s/cm^2 in 0.5-4.0 keV.
A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an X-ray source was detected around 3 minutes later at R.A. = 273.0416 deg, DEC = 18.7062 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). The estimated FXT flux is around 2e-11 erg/s/cm^2 in 0.5-10.0 keV. We note that a historical ROSAT source (1RXS J181210.7+184228) positioned just 12 arcseconds from our FXT detection coordinates, with a flux about three orders of magnitude lower than the present WXT measurement.
Further information will be updated when the telemetry data is received.
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).