TITLE: GCN CIRCULAR NUMBER: 39420 SUBJECT: EP250220a: EP-FXT follow-up observations DATE: 25/02/22 08:11:55 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn

D. F. Hu (PMO, CAS), Y. L. Wang (NAOC, CAS), P. Y. Han, C. X. Zhang (HUST), B. B. Zhang (BNU), Y. Liu (NAOC, CAS) report on behalf of the Einstein Probe team:

Following the detection of the fast X-ray transient EP250220a (Wang et al., GCN 39387), we performed two follow-up observations with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission.

The first FXT observation started at 2025-02-20 14:59:57 (UTC), about 13 hours after the WXT detection, with an exposure of ~ 3 ks. Within the WXT error circle, one faint X-ray source was detected by one of the FXT modules, at the position of R.A. = 113.4516 deg, DEC = 39.8098 deg (J2000), with an uncertainty of 10 arcsec in radius (90% C. L. statistical and systematic). The detection is relatively weak and the spectrum is not well fitted.

The second FXT observation started at 2025-02-21 10:12:09 (UTC), about 32 hours after the WXT detection, with an exposure of ~ 7 ks. No source was detected within the WXT error circle. Assuming a photon index of 1.1 and Galactic absorption with NH = 7.13 x 10^20 cm^-2, we derive an upper limit of 1.90e-14 erg/s/cm^2 (0.5-10 keV; 90% C. L.).

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).

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