Einstein Probe detection of a new outburst from RX J1709.5-2639 (XTE J1709-267)
ATel #17212; Q. Y. Wu, W. J. Zhang (NAO, CAS), C. Y. Dai (NJU), W. M. Yuan (NAO, CAS) on behalf of the Einstein Probe (EP) team:
on 31 May 2025; 10:12 UT
Credential Certification: Yuan Liu (liuyuan@bao.ac.cn)
We report on the detection of a new X-ray outburst from the low-mass X-ray binary (LMXB) RX J1709.5-2639 (XTE J1709-267), by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The source exhibited a gradual flux increase since May 25 and triggered EP-WXT (ID: 01709177494) at 2025-05-31T01:46:22 (UTC). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically from ~4 minutes after the trigger. The WXT and FXT spectra around the trigger time can be fitted simultaneously by an absorbed power-law with a photon index of 2.02 (+0.03/-0.03) and a neutral hydrogen column density of 3.9 (+0.1/-0.1) x 10^21 cm^-2. The derived unabsorbed flux in 0.5-4 keV is 4.5 (+0.1/-0.1) x 10^-10 erg/s/cm^2.
We note that RX J1709.5-2639 exhibited several outbursts since 2004 (ATel #2729, #4304, #5319, #5332, #9108, #9181, #10671, #14047). The last outburst was reported by MAXI team on October, 2023 with a flux of 30-40 mCrab in 2-10 keV (ATel #16283). Several smaller outbursts were also detected by EP-WXT from June to April, 2024, with a peak flux of around 1.8 x 10^(-10) erg/s/cm^2 in 0.5-4 keV.
Multi-wavelength follow-up observations are encouraged.
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).
