GCN Circular 39165
Subject
EP250205a/GRB 250205A: Einstein Probe observation
Date
2025-02-06T09:14:37Z (5 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
Z. Y. Liu (USTC), M. H. Zhang, M. J. Liu, H. N. Yang, W. Yuan (NAO, CAS) report on behalf of the Einstein Probe team
We report on the detection of an X-ray transient, designated EP250205a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, which triggered the on-board processing unit at 2025-02-05 21:32:08 (UTC) (trigger ID: 01709131283). The source position is R.A. = 113.522 deg, DEC = 32.363 deg (J2000) with an uncertainty of about 2.5 arcmin (radius, 90% C.L. statistical and systematic). An autonomous follow-up observation of EP250205a was performed by the Follow-up X-ray Telescope (FXT) on board EP, 256s after the WXT trigger. An uncatalogued X-ray source was detected at R.A. = 113.509 deg, DEC = 32.373 deg (J2000) with an uncertainty of less than 10 arcsec (radius, 90% C.L. statistical and systematic), consistent with the WXT position of EP250205a.
The 0.5-4.0 keV WXT spectrum can be fitted with an absorbed power law with a fixed Galactic absorption with column density 4.4 x 10^20 cm^-2 and an intrinsic absorber with a redshift of 3.55. The fitted equivalent hydrogen column density of the intrinsic absorber is 6.5(+9.8/-6.5) x 10^22 cm^-2, the photon index 2.5(+1.7/-1.2), and the unabsorbed 0.5-4 keV flux 4.2 (+1.1/-1.1) x 10^-10 erg/s/cm^2.
The average 0.5-10 keV spectrum of the follow-up observation obtained by EP-FXT can be fitted with an absorbed power law with a photon index of 2.82 (+0.06/-0.04) (with a galactic column density fixed at 4.4 x 10^20 cm^-2), yielding an average unabsorbed 0.5-10 keV flux of 3.65 (+0.07/-0.09) x 10^-11 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
EP250205a is spatially and temporally consistent with GRB 250205A (Saccardi et al. GCN 39154) at a redshift of 3.55 (de Ugarte Postigo et al. GCN 39160). EP250205a was first detected by WXT at 2025-02-05T21:31:28 (UTC), about 410 seconds after the SVOM/ECLAIRs trigger time (2025-02-05T21:24:38), due to Earth obscuration of the WXT FoV from 2025-02-05T20:26:42 to 2025-02-05T21:31:28.
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). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES.