TITLE: GCN CIRCULAR NUMBER: 38430 SUBJECT: EP241201a: EP-FXT follow-up observations DATE: 24/12/03 15:57:18 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn

W. Chen (NAO, CAS), G. Y. Zhao (SYSU), C. Zhou (HUST), T. Zhao (NAO, CAS), W. D. Zhang (NAO, CAS) report on behalf of the Einstein Probe team:

Following the detection of the fast X-ray transient EP241201a (Chen et al., GCN 38415), we performed an observation with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe mission. The observation started at 2024-12-02T09:23:55 (UTC), about 12 hours after the EP-WXT detection, with an exposure time of 2.9 ks. Within the WXT error circle, an uncatalogued X-ray source is detected at R.A. = 282.4865 deg, DEC = 66.0693 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). The average FXT spectrum in 0.5-10 keV can be fitted by an absorbed power law with a photon index of 4.8(-1.5,+1.7) and a column density of 1.2(-0.5,+0.6) x 10^22 cm^-2, giving an average unabsorbed flux of 2.9(-2.0, +14.4) x 10^-12 erg/s/cm^2 in the 0.5-10 keV band. Compared to the WXT detection, its flux has droped by about three orders of magnitude. The X-ray spectrum in 0.5-10 keV can also be fittted by an absorbed black body with a temperature of 0.27(-0.06, +0.08) keV and a column density of 4.9(-3.2, +4.0) x 10^21 cm^-2, giving an average unabsorbed flux of 3.9(-1.5, +3.7) x 10^-13 erg/s/cm^2.

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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