TITLE:   GCN CIRCULAR
NUMBER:  44142
SUBJECT: EP260329b: Einstein Probe detection of an X-ray transient
DATE:    26/03/29 12:07:29 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

F.-F. Song (YNAO, CAS), Guojiong Yang, Wei Chen, Yuan Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team:

We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260329b. The transient triggered EP-WXT (ID: 01709259209) at 2026-03-29T10:36:00 (UTC). The WXT position of the source is R.A. = 181.309 deg, DEC = 4.362 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic).

A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 181.3122 deg, DEC = 4.3526 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). The FXT position is consistent with the optical counterpart reported by Li et al. (GCN 44139) and Zhu et al. (GCN 44140).

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).