EP260903a
GCN Circular 45522
Subject
EP260903a: EP-FXT follow-up observation
Date
2026-09-06T15:15:50Z (5 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Z.-M. Wang (BNU), R.-Z. Li (YNAO, CAS), R. Shi (PMO, CAS), H. Sun (NAO,CAS) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a follow-up observation of EP260903a detected by EP-WXT (Wang et al., GCN 45513). The observation started at 2026-09-04T06:25:52Z, about 18.8 hr after the WXT detection, with a total exposure time of around 4.8 ks.
On-ground analysis of the FXT data found 1 uncatalogued X-ray source with a low S/N of approximately 3.5 at:
R.A. (J2000) = 292.0071 deg
Dec. (J2000) = -21.5004 deg
with an uncertainty radius of 10 arcsec in radius (90% confidence level). The average FXT 0.5-10 keV spectrum can be fitted by an absorbed power-law model with a fixed Galactic hydrogen column density of 8.0×10^20 cm^-2 and a photon index of 3.36 (-1.25/+1.46). The derived average unabsorbed 0.5-10 keV flux is 6.89 (-2.79/+3.01) x 10^-14 erg cm^-2 s^-1. The uncertainties are at the 90% confidence level for the above parameters.
Launched on January 9, 2024, EP is a space X-ray observatory designed to monitor the dynamic soft X-ray sky and perform follow-up observations of newly discovered transients (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
GCN Circular 45513
Subject
EP260903a: EP-WXT detection of a fast X-ray transient
Date
2026-09-04T08:19:20Z (8 days ago)
Edited On
2026-09-06T15:29:45Z (5 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Z.-M. Wang (BNU), R.-Z. Li (YNAO, CAS), R. Shi (PMO, CAS), H. Sun (NAO,CAS) on behalf of the Einstein Probe (EP) team:
We report on the detection of a fast X-ray transient, designated EP260903a (notice ID: 13600875138), by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient was identified in the telemetry data. The WXT light curve of the transient started at about 2026-09-03T11:17:59 (UTC) and lasted for approximately 200 s, exhibiting a double-peaked structure. The position of the transient is R.A. = 292.004 deg, Dec. = -21.494 (J2000), with an uncertainty radius of 2.6 arcmin in radius (90% confidence level, including both statistical and systematic uncertainties).
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 8.0×10^20 cm^-2 and a photon index of 1.67 (-0.54/+0.60). The derived average unabsorbed 0.5-4 keV flux is 7.41 (-2.21/+2.90) x 10^(-10) erg cm^-2 s^-1. The uncertainties are at the 90% confidence level for the above parameters.
Follow-up observations by EP-FXT has be scheduled.
The optical follow-up observation was performed by MASTER-Net (Gress et al., GCN 45512).
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).