EP-WXT detection of on-going X-ray brightening likely from LS V +44 17

ATel #18063; Tian-Yu Liu(NAOC), K. R. Ni (CCNU), S. Q. Zheng, Jin-Rui Liu (BNU), G. J. Yang, B. B. Zhang and Z.-X. Ling (NAO, CAS), on behalf of the Einstein Probe (EP) team:
on 20 Sep 2026; 18:56 UT
Credential Certification: Yuan Liu (liuyuan@bao.ac.cn)

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We report on the detection of X-ray brightening, likely from LS V +44 17, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The onset of the brightening was detected by EP-WXT since 2026-09-14. Before that, the 0.5-4 keV unabsorbed flux of the source as measured by WXT is less than ~1x10^-11 erg/s/cm2. After the onset, the flux has been increasing, to a level of 1.4x10^-10 erg/s/cm2 on 2026-09-20 when the most recent WXT observation of the source was taken.

An autonomous follow-up observation was performed with the Follow-up X-ray Telescope (FXT) on board EP. The refined position is at RA = 70.2524 deg, DEC = 44.5297 deg (J2000), with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). The position is consistent with that of LS V +44 17. The estimated 0.5-10.0 keV flux is approximately 3.1x10^-10 erg/cm^2/s. 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). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES.