TITLE: GCN CIRCULAR NUMBER: 41861 SUBJECT: EP250916a: EP-FXT follow-up observation DATE: 25/09/18 07:46:30 GMT FROM: EP Team at NAOC/CAS <ep_ta@bao.ac.cn> C. Y. Dai (NJU), Q. Y. Wu, D. Y. Li, H. W. Pan (NAO, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation of EP250916a (GCN 41841) at 2025-09-17 11:34:24 (UTC), about 32 hours after the WXT detection, with an exposure time of 3.1 ks. FXT detected a bright source within the WXT error circle at R.A. = 268.2379 and Dec. = –35.3222 (J2000), with a positional uncertainty of 10 arcseconds (radius, 90% confidence level, including both statistical and systematic errors). The fit with a power-law spectrum yields Nh = 3.1 × 10^21 cm^-2 and a photon index of 1.66 ± 0.02, with a 0.5–10 keV flux of 5.4 × 10^-10 erg/s/cm^2. Additionally, we note that this source keeps brightening in the WXT monitoring, with the flux rising from approximately 3 × 10^-11 erg/s/cm^2 at 2025-09-16 03:33:13 to about 2 × 10^-10 erg/s/cm^2 at 2025-09-17 17:54:10 (UTC). Further follow-up observations are encouraged to identify the nature of this source. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/41861. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...