TITLE: GCN CIRCULAR NUMBER: 40403 SUBJECT: EP250508a: follow-up observation with EP-FXT DATE: 25/05/09 08:07:31 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn
R. D. Liang, T. Zhao, H. Q. Cheng, W. D. Zhang (NAOC, CAS) on behalf of the Einstein Probe (EP) team:
Following the detection of the fast X-ray transient EP250508a (Liang et al., GCN 40390, Zhao et al. GCN 40399) and its multi-wavelength follow-up observations (Postigo et al., GCN 40391; Lipunov et al., GCN 40393; Brivio et al., GCN 40395; Zheng GCN 40401; Xin et al. GCN 40402), we performed an observation with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe mission.
The observations began at 2025-05-08 13:41:03 (UTC), about 7.6 hours after the EP-WXT detection. The exposure time is 7250 seconds. Preliminary analysis shows that the source was detected in this epoch. The spectrum in the 0.5-10 keV band can be fitted with an absorbed power-law model with NH fixed at the Galactic value of 3.56e20 cm^-2 and a photon index of 2.22(-0.47, +0.47). The unabsorbed 0.5-10 keV flux is 4.53(-1.88, +1.88)e-14 erg/s/cm^2 (90% C.L.), about five times lower than that detected in the autonomous FXT follow-up observation (Zhao et al. GCN 40399), demonstrating a rapid decay trend in the source's X-ray emission.
EP-FXT will continue monitoring the source. More follow-up observations are encouraged. The contact TA of EP250508a is R. D. Liang. Please contact him via email liangrd@bao.ac.cn if needed.
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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