TITLE:   GCN CIRCULAR
NUMBER:  45661
SUBJECT: EP-WXT detected a brightening of HMXB LS V +44 17
DATE:    26/09/20 18:02:54 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

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:

We report on the detection of X-ray brighening, likely from High Mass X-ray Binary(HMXB) LS V +44 17, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The burst triggered EP-WXT (ID: 01709318523) at the time of 2026-09-20 15:53:04 UTC. The WXT position of the source is R.A. = 70.241 deg, DEC = 44.538 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 1.4 x 10^-10 erg/cm^2/s, which is an order of magnitude higher than the previous detection before 2026-09-14. 

A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. An X-ray source was detected at R.A. = 70.2524 deg, DEC = 44.5297 (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic), which is consistent with the position of LS V +44 17. The estimated flux in the 0.5-10 keV band is around 3.1 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).