TITLE: GCN CIRCULAR NUMBER: 39591 SUBJECT: EP250304a: refined analysis of the EP-WXT and EP-FXT observations DATE: 25/03/04 14:33:38 GMT FROM: EP Team at NAOC/CAS ep_ta@bao.ac.cn
Y.J. Zhang (THU), C. Y. Dai (NJU), W. Chen, W. X. Wang (NAO, CAS), Y. Liu (NAO, CAS) report on behalf of the Einstein Probe team:
The X-ray transient EP250304a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Chen et al., GCN 39580), and followed up by several telescopes (Xu et al, GCN 39583, Page et al., GCN 39584, Saccardi et al., GCN 39585, Shilling et al., 39587), with an optical counterpart detected at a redshift of 0.200 (Saccardi et al., GCN 39585). Refined analysis of the WXT data shows that the event started at T0=2025-03-04T01:29:49 (UTC) and lasted for about 1200 s. The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 5 x 10^20 cm^-2 and a photon index of 2.2 (-/+0.1). The derived average unabsorbed 0.5-4 keV flux is 5.3(-/+0.4) x 10^(-10) erg/s/cm^2.
The Follow-up X-ray Telescope (FXT) on board EP observed this source autonomously about 200 seconds after T0. On-ground analysis of the FXT data found an uncatalogued source at R.A. = 208.3953, DEC = -42.8050 (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic), which is consistent positionally with the WXT transient. The FXT observation suffered from significant pile up at the begining of the observation. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a Galactic hydrogen column density of 5 x 10^20 cm^-2 and a photon index of 2.11 (-/+0.05). The derived average unabsorbed 0.5-10 keV flux is 1.75 (-/+0.06) x 10^(-10) erg/s/cm^2 during the time interval from 500 to 1200 seconds after the start of the observation. Further FXT observation started about 4000 seconds after the trigger and showed an average unabsorbed 0.5-10 keV flux of 6.5 (-2.3/+3.5) x 10^(-12) erg/s/cm^2 with an exposure time of about 300 seconds. 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).
View this GCN Circular online at https://gcn.nasa.gov/circulars/39591. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...