EP260628a
GCN Circular 45057
Subject
EP260628a: EP-FXT follow-up observation
Date
2026-06-30T02:51:19Z (15 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
X. Mao (NAO, CAS), C. Y. Dai (NJU), H. N. Yang, C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a follow-up observation of EP260628a (X. Mao et al., GCN 45054) starting at 2026-06-29T06:40:57 (UTC), approximately 13.5 hours after the WXT detection. With an exposure time of 1.5 ks, no significant X-ray source was detected within the 2.8 arcmin radius of the EP-WXT position. The derived 0.5-10 keV upper limit is about 3.7 x 10^(-13) erg cm^-2 s^-1.
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 Circular 45054
Subject
EP260628a: EP-WXT detection of a fast X-ray transient
Date
2026-06-29T03:22:43Z (16 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
X. Mao, H. N. Yang (NAO, CAS), C. Y. Dai(NJU), C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team:
We report on the detection of a fast X-ray transient, designated EP260628a, 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 2026-06-28T17:08:08 (UTC) and lasted for about 30s, with a peak flux of ~ 7 x 10^(-9) erg cm^-2 s^-1 in 0.5-4 keV. The position of the transient is R.A. = 312.9884 deg, Dec. = -34.3748 (J2000), with an uncertainty radius of 2.8 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 4.86×10^20 cm^-2 and a photon index of 0.67 (-0.52/+0.52). The derived average unabsorbed 0.5-4 keV flux is 1.87 (-0.54/+0.71) x 10^(-9) 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).