GCN Circular 42915

 
W. J. Zhang (NAO, CAS), H. C. Ding, T. Wu (AHNU), Y. H. Jiang, Y. Wu (NJU), Y. Wang (PMO), Y. Liu (NAO, CAS), on behalf of the Einstein Probe (EP) team:
 
The fast X-ray transient EP251130a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Wu et al., GCN 42903
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 ), and was followed by several telescopes (Dornic et al., GCN 42904
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 , Lipunov et al., GCN 42906
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  and Evans et al., GCN 42908
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 ). The refined analysis of the WXT data shows that the event started at T0=2025-11-30T11:04:00 (UTC) and lasted for ~230 s, before the observation was interrupted by the autonomous follow-up observation. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.40 x 10^21 cm^-2 and a photon index of 1.54 (-0.63/+0.70). The derived average unabsorbed 0.5-4 keV flux is 2.46 (-0.77/+1.06) x 10^(-10) erg/s/cm^2.

A follow-up observation of EP251130a with the Follow-up X-ray Telescope (FXT) was performed automatically at 2025-11-30T11:11:12 (UTC), about 7 minutes after T0, with an exposure time of 4,200 s. The on-ground analysis shows that an uncatalogued source was detected at R.A. = 101.0210 deg, Dec. = 27.3840 deg (J2000) with an uncertainty of 10 arcsec in radius (90% C.L. statistical and systematic). This position is ~1.6 arcsec from the reported optical counterpart (Dornic et al., GCN 42904
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 ). The average FXT 0.5-10 keV spectrum of the observation can be fitted with an absorbed power law, with a hydrogen column density of 1.39 (-0.81/+0.86) x 10^21 cm^-2 and a photon index of 2.12 (-0.32/+0.34). The derived average unabsorbed 0.5-10 keV flux is 3.32 (-0.31/+0.32) x 10^(-12) 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).