GCN Circular 41716
Subject
EP detected a brightening of LMXB 1ES 1735-26.9
Date
2025-09-05T07:07:13Z (5 days ago)
Edited On
2025-09-05T13:21:08Z (5 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
R. D. Liang (NAOC), Y. Wang (PMO), Y.H.Cheng (SWIFAR,YNU), W. D. Zhang (NAOC) 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: 01709201259) at the time of 2025-09-05T05:11:45 UTC. The WXT position of the source is R.A. = 264.569 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 5 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. = 264.5679 deg, DEC = -26.9927 (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 2 x 10^-10 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).