TITLE: GCN CIRCULAR NUMBER: 42808 SUBJECT: EP251122a: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/11/23 03:13:31 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn
Y.-H. I. Yin (HKU), B.-T. Wang (YNAO), G. J. Yang (NAOC), H.-Z. Wu (HUST) and W. D. Zhang (NAOC) on behalf of the Einstein Probe (EP) team:
The fast X-ray transient EP251122a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Wang et al., GCN 42799) and SVOM/ECLAIRs as GRB 251122A (Lin et al, 42800), and followed by several optical telescopes (Wu et al., GCN 42801, Lipunov et al., GCN 412802, Cheng et al., GCN 42803, Saccardi et al., GCN 42804, Cotter et al., GCN 42805, Li et al., GCN 42806, Sun et al., GCN 42807). The refined analysis of the WXT data shows that the event started at T0=2025-11-22T13:53:43 (UTC) and lasted for 10 s with a single pulse, 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 1.33 x 10^21 cm^-2 and a photon index of 1.26 (-0.58/+0.59). The derived average unabsorbed 0.5-4 keV flux is 2.07 (-0.67/+0.77) x 10^(-9) erg/s/cm^2. The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed at 2025-11-22T13:57:19 (UTC), about 4 minutes after T0. The exposure time of this observation is 6029 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 38.0220, 14.1283 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The light curve displays two pulses structure lasting for around 400 s. The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 1.33 x 10^21 cm^-2 and a photon index of 1.74 (-0.05/+0.04). The derived average unabsorbed 0.5-10 keV flux is 7.66 (-0.30/+0.33) x 10^(-11) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
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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