TITLE:   GCN CIRCULAR
NUMBER:  45201
SUBJECT: EP260723a: EP-WXT detection of a fast X-ray transient
DATE:    26/07/24 06:57:32 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

Y.J. Zhang (PKU), K. R. Ni (CCNU), X. H. Tang (THU), H. Sun (NAOC) on behalf of the Einstein Probe (EP) team:              

We report on the detection of a fast X-ray transient, designated EP260723a (trigger ID: 11916655551), by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient started at 2026-07-23T18:56:01 (UTC) and lasted for about 100s, with a peak flux of ~ 1.4 x 10^(-9) erg cm^-2 s^-1 in 0.5-4 keV. The position of the transient is R.A. = 2.938 deg, Dec. = -12.112 (J2000), with an uncertainty radius of 3 arcmin in radius (90% confidence level, including both statistical and systematic uncertainties). 

The average WXT 0.5-4 keV spectrum can be fitted by an absorbed power-law model with a fixed Galactic hydrogen column density of 2.0×10^20 cm^-2 and a photon index of 1.4 (-0.8/+0.9). The derived average unabsorbed 0.5-4 keV flux is 4.1(-1.6/+2.7) x 10^(-10) erg cm^-2 s^-1. The uncertainties are at the 90% confidence level for the above parameters.

Follow-up observations by EP-FXT will be arranged.

Launched on 2024 January 9, Einstein Probe is a space-based X-ray observatory designed to monitor the dynamic X-ray sky and perform rapid follow-up observations of newly discovered transients (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).