GCN Circular 45893
Subject
EP261010a: refined analysis of the EP-WXT and autonomous EP-FXT observations
Event
Date
2026-10-11T05:11:11Z (15 hours ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
A.Li (BNU), C.Y. Wang (THU), H.Z. Wu (HUST), C.L.Guo, H.Sun (NAO, CAS), on behalf of the Einstein Probe (EP) team:
The X-ray transient EP261010a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission at 2026-10-10T00:18:44 (UTC, Li et al., GCN 45880). The refined analysis of the WXT data shows that the event started at T0 = 2026-10-10T00:17:40 (UTC). The transient light curve shows a rising trend and lasted around 70s before the interruption by the autonomous follow-up. Subsequent follow-up observations were reported by Buckley et al. (GCN 45881), Zhu et al. (GCN 45882) and Ma et al. (GCN 45884).
The time-averaged WXT spectrum in the 0.5–4 keV band is extremely soft and can be fitted with an absorbed blackbody model. The hydrogen column density was fixed at the Galactic value of NH = 2.11 × 10^20 cm^-2 at the source position. The best-fit temperature is 0.26 (+0.12/-0.08) keV. The average unabsorbed 0.5–4 keV flux is 1.2 (+0.7/-0.6) × 10^-10 erg s^-1 cm^-2.
The autonomous observation of the Follow-up X-ray Telescope (FXT) on board EP started at 2026-10-10T00:20:35 (UTC), around 110 s after the WXT trigger. Both FXT-A and FXT-B detected an uncatalog X-ray source within the WXT error region at R.A. = 26.2203 deg, Dec. = -34.0870 deg (J2000). We jointly fitted the FXT-A and FXT-B spectra in the 0.5–10 keV band with an blackbody model. The hydrogen column density was fixed at the Galactic value. The best-fit temperature is 0.10(+0.03/-0.04) keV. The average unabsorbed 0.5–10 keV flux is 7.6 (+3.6/-2.9) × 10^-14 erg s^-1 cm^-2. All quoted uncertainties on the spectral parameters and fluxes are at the 90% confidence level.
The soft thermal spectrum and the rapid temporal decline of the X-ray emission suggest that EP261010a could be a supernova shock breakout candidate. The follow-up observation with the EP-FXT has been scheduled to monitor its further evolution.
Launched on January 9, 2024, EP is a space-based X-ray observatory designed to monitor the soft X-ray sky and perform X-ray follow-up observations (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).