TITLE: GCN CIRCULAR NUMBER: 39266 SUBJECT: EP250207b: a new X-ray transient detected by Einstein Probe DATE: 25/02/10 09:16:09 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn
X.-Y. Zhou (PRIC), A. Li (BNU), D.-H. Zhao, X.-P. Xu, Q.-Y. Wu and Y. Liu (NAOC, CAS) report on behalf of the Einstein Probe team:
We report on the detection of an X-ray transient, designated EP250207b, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient event started at T0=2025-02-07T21:47:56(UTC) and lasted for more than 120 s before the observation ended. The WXT position of the source is R.A. = 167.495 deg, DEC = -7.906 deg (J2000) with an uncertainty of 2.7 arcmin in radius (90% C.L. statistical and systematic). The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 4.24 x 10^20 cm^-2 and a photon index of 0.6 (-0.8/+0.8). The derived average unabsorbed 0.5-4 keV flux is 6.1 (-2.5/+4.2) x 10^(-10) erg/s/cm^2.
Two ToO observations were performed by the Follow-up X-ray Telescope (FXT) . The first observation started at 2025-02-08T14:52:06 (~T0+17h) with an exposure time of 3024 s. An uncatalogued source was detected at R.A. = 167.5130, DEC = -7.8695 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). 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 4.24 x 10^20 cm^-2 and a photon index of 1.5 (-0.6/+0.6), giving an average unabsorbed 0.5-10 keV flux of 3.6 (-1.4/+3.5) x 10^(-13) erg/s/cm^2. The second observation started at 2025-02-09T18:10:59 (~T0+44h) with an exposure time of 5042 s. The uncatalogued source was detetcted with a declined flux of 6.4 (-2.8/+3.5) x 10^(-14) erg/s/cm^2, indicating its correlation with EP250207b. The uncertainties are at the 90% confidence level for the above parameters.
Further follow-up observations are encouraged to identify the nature of this X-ray transient.
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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