GCN Circular 45410

Tian-Yu Liu (NAO, CAS), Xin-Xiang Sun (NAO, CAS), Y.J. Yi (BNU) , Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team:

We report on the detection of X-ray brightening of Low Mass X-ray Binary (LMXB) 1ES 1735-26.9 by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The burst triggered EP-WXT (ID: 01709285030) at the time of 2026-08-20 07:27:33 UTC. The WXT position of the source is R.A. = 264.58 deg, DEC = -26.997 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The estimated flux in the 0.5-4 keV band is around 8.80 x 10^-10 erg/cm^2/s, which is an order of magnitude higher than the previous detection.

A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. An X-ray source was detected at R.A. = 264.5673 deg, DEC = 26.9930 (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic), which is consistent with the position of known LMXB 1ES 1735-26.9. The estimated flux in the 0.5-10 keV band is around 1.95 x 10^-9 erg/cm^2/s.

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).