TITLE:   GCN CIRCULAR
NUMBER:  44153
SUBJECT: EP260329a: EP-FXT follow up observation
DATE:    26/03/30 06:40:23 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

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

The fast X-ray transient EP260329a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Yang et al., GCN 44141). Early optical follow-up observations reported only upper limits (Sankar et al., GCN 44145). A possible uncatalogued optical counterpart was reported by later optical observations (He et al., GCN 44152).

EP-FXT performed a follow-up observation starting at 2026-03-29T14:47:27 UTC, approximately 11.3 hours after the WXT trigger, with a total exposure time of 5934 s. Two uncataloged sources are detected within the WXT error circle. Preliminary analysis on these sources is automatically conducted, and the details are listed as follows.

EPF_J002151.2+822924
RA (J2000): 5.4918, 
Dec (J2000): 82.4881
Flux: 4.9e-14 erg/s/cm^2 (observed, 0.5-10 keV)
Flux_err: 1.3e-14 erg/s/cm^2 (1 sigma)

EPF_J002212.3+823200
RA (J2000): 5.5758
Dec (J2000): 82.5335
Flux: 5.3e-14 erg/s/cm^2 (observed, 0.5-10 keV)
Flux_err: 1.5e-14 erg/s/cm^2 (1 sigma)

We note that the position of EPF_J002151.2+822924 is consistent with the optical uncatalogued counterpart reported by GCN 44152 (He et al.)

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).