TITLE:   GCN CIRCULAR
NUMBER:  46125
SUBJECT: EP261030a: EP-FXT follow-up observation
DATE:    26/11/01 15:35:36 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

H.-H. Zhang, C.-Y. Dai (NJU), Y.-L. Wang (ICE, CSIC) and Y. Liu (NAOC) on behalf of the Einstein Probe (EP) team:

The X-ray transient EP261030a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Zhang et al., GCN 46121) at 2026-10-30T17:15:19 (UTC). No optical counterpart was detected in follow-up observations with MASTER-SAAO (Buckley et al., GCN 46122) or the GROWTH-India Telescope (Sarkar et al., GCN 46124). 
Follow-up observation by the Follow-up X-ray Telescope (FXT) on board EP was performed at 2026-10-31 23:08:47(UTC), ~30 hours after the WXT detection. The exposure time of the observation is around 4 ks. On-ground analysis of the FXT data revealed an X-ray source within the WXT error circle of EP261030a. The source is located at R.A. = 23.6760 deg and Dec. = -11.6749 deg (J2000), with an uncertainty radius of 10 arcsec (90% confidence level, including both statistical and systematic errors). The source lies within the WXT error circle of EP261030a.
The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 2.4E20 cm-2 and a photon index of 1.4(-0.77, +0.84). The derived flux in 0.5-10 keV is 1.6(-0.9, +2.2)E-13 erg/s/cm2. The uncertainties are at the 90% confidence level for the above parameters. 

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).