TITLE: GCN CIRCULAR NUMBER: 42166 SUBJECT: GRB 251006B/EP251006a: EP-FXT afterglow detection DATE: 25/10/08 11:48:28 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn
Y.-H. I. Yin (HKU), M. H. Zhang, T. Y. Liu, H. Y. Ren and Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a second follow-up observation of GRB 251006B/EP251006a (GCN 42131, GCN 42137, GCN 42139, GCN 42155) at 2025-10-07T18:08:41 (UTC), about 22 hours after the WXT detection, with an exposure time of 4.9 ks. The source was also followed by several optical telescopes (GCN 42133, GCN 42138, GCN 42141). Two uncatalogued sources were detected within the WXT error circle (GCN 42140), of which Source 2 has faded with an unabsorbed flux of 3.37 x 10^-13 erg/s/cm^2 (22 hours) from the first observation at about 3.52 x 10^-12 erg/s/cm^2 (11 hours) in 0.5-10 keV. The position of Source 2 is R.A. = 40.5195 deg, DEC = -6.0346 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic), which is consistent with the SVOM/VT optical candidate (GCN 42141), and is therefore likely the GRB afterglow.
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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