TITLE: GCN CIRCULAR NUMBER: 39700 SUBJECT: EP250311a/GRB 250311A: EP-FXT follow-up observation DATE: 25/03/13 07:52:04 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn

X. Mao (NAO, CAS), Y. J. Zhang (THU), Y. L. Hua (PMO, CAS), Z. X. Ling (NAO, CAS) report on behalf of the Einstein Probe team:

Following the detection of the fast X-ray transient EP250311a (Mao et al., GCN 39664), also detected as GRB 250311A by MAXI (Tatano et al., GCN 39660), we performed an observation with the Follow-up X-ray Telescope (FXT) on board Einstein Probe. The observation began at 2025-03-12T15:29:21 (UTC), about 38 hours after the EP-WXT detection, with an exposure time of 6048 seconds. Two uncatalogued sources were detected within the WXT error circle, at R.A., DEC = 224.7009, -2.8412 deg (J2000) and R.A., DEC = 224.7199, -2.8760 deg (J2000), respectively, with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). Both of the sources have the flux at the level of ~ 5e-14 erg/cm2/s in 0.5-10 keV. No previously known X-ray sources are found within the FXT error circle around the two sources.

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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