GCN 44786: EP260602b: Einstein Probe detection of a fast X-ray transient
2026-06-03T06:14:44.361Z | rev 0
J. W. Hu (NAO, CAS), Z. X. Li, G. L. Huang, J. Y. Cao (IHEP, CAS), Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team:
We report on the detection of a fast X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260602b. The transient triggered EP-WXT (ID: 01709266414) at 2026-06-02T17:54:02 (UTC). The WXT position of the source is R.A. = 273.487 deg, DEC = 7.595 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic).
The refined analysis of the WXT data shows that the event was detected at R.A. = 273.483 deg, DEC = 7.579 deg (J2000) with an uncertainty of 2.6 arcmin in radius. The event started at T0=2026-06-02T17:53:12 (UTC), and lasted for about 60 s. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.9 × 10^21 cm^-2, and a photon index of 1.36 (-0.80, +0.87). The derived average unabsorbed 0.5-4 keV flux is 1.8 (-0.6, +0.7)×10^(-9) erg/s/cm^2.
The optical counterpart of EP260602b was reported by He et al. (GCN 44780).
No autonomous follow-up observation with Follow-up X-ray Telescope (FXT) was performed. A Target-of-Opportunity observation with the FXT has been scheduled. 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).
GCN 44780: EP-WXT trigger 01709266414 (EP260602b): JinShan optical counterpart detection
2026-06-03T02:11:44.736Z | rev 0
L.B. He, X. Liu, Z.P. Zhu, D. Xu, J. An, S.Q. Jiang (NAOC), S.Y. Fu, A.D. Zhu, L. Lei (HUST), J.Z. Liu (XAO) report:
We observed the field of EP-WXT Trigger 01709266414 (presumably EP260602b) detected by Einstein Probe (EP), using the JinShan 100B and 100C telescopes located at Altay, Xinjiang, China. A series of r-band frames were obtained.
An uncatalogued and decaying source is detected within the EP/WXT error circle at coordinates
R.A. (J2000) = 18:13:53.7 (273.4738 deg)
Dec. (J2000) = +07:34:16.4 (7.5712 deg)
with an uncertainty of ~ 1.0 arcsec. The source had r ~ 19.0 mag at a median time of ~ 1.0 hr post-trigger, calibrated with Pan-STARRS DR2 and not corrected for Galactic extinction of A_V ~ 0.94 mag. We thus think the source is the optical counterpart.
We acknowledge the excellent support from T.Q. Chen and J.F. Zhang for enabling these observations.