TITLE:   GCN CIRCULAR
NUMBER:  46166
SUBJECT: GRB 261104A：EP-FXT follow-up observation
DATE:    26/11/06 03:57:29 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

B. B. Zhang, C. L. Guo, Q.Y. Wu, W.D. Zhang (NAO, CAS), Y. Q. Zhao(PRIC, USTC)
 on behalf of the Einstein Probe (EP) team: 

EP-FXT performed a follow-up observation of GRB 261104A, detected by SVOM/ECLAIRs (Bernardini et al., GCN 46150), which was also observed in optical by LCO 1m telescope (Yin et al., GCN 46154), SVOM/VT (Li et al., GCN 46161), and DECam (Davis et al., GCN 46164). The observation started at 2026-11-05 19:31:07 (UTC), about 23 hrs after the SVOM/ECLAIRs trigger, with an exposure time of 1871 s. 

On-ground analysis of the EP-FXT data found six uncataloged X-ray source within the SVOM/ECLAIRs error region (Bernardini et al., GCN 46150). None of these sources has a position consistent with that of the optical counterpart candidate. The preliminary results for the X-ray source are as follow: 

Source 1: EPF_J002511.2-542737
R.A., Decl. (J2000) = 6.2972, -54.4603 deg 
Localization error radius = 10 arcsec 0.5-10 keV 
Flux = 3.13e-13 erg/cm^ 2/s 
Flux error = 7.15e-14 erg/cm^2/s (1 sigma) 
Separation = 0.13 arcmin 

Source 2: EPF_J002543.1-543011
R.A., Decl. (J2000) = 6.4296, -54.5032 deg 
Localization error radius = 10 arcsec 0.5-10 keV 
Flux = 1.98e-13 erg/cm^ 2/s 
Flux error = 5.99e-14 erg/cm^2/s (1 sigma) 
Separation = 5.3 arcmin

Source 3: EPF_J002439.7-542315
R.A., Decl. (J2000) = 6.1655, -54.3874 deg 
Localization error radius = 10 arcsec 0.5-10 keV 
Flux = 1.10e-13 erg/cm^ 2/s 
Flux error = 8.14e-14 erg/cm^2/s (1 sigma) 
Separation = 6.4 arcmin

Source 4: EPF_J002458.6-543125
R.A., Decl. (J2000) = 6.2441, -54.5236 deg 
Localization error radius = 10 arcsec 0.5-10 keV 
Flux = 1.12e-13 erg/cm^ 2/s 
Flux error = 4.23e-14 erg/cm^2/s (1 sigma) 
Separation = 4.1 arcmin

Source 5: EPF J002428.2-542321
R.A., Decl. (J2000) = 6.1177, -54.3891 deg 
Localization error radius = 10 arcsec 0.5-10 keV 
Flux = 1.83e-13 erg/cm^ 2/s 
Flux error = 5.22e-14 erg/cm^2/s (1 sigma) 
Separation = 7.6 arcmin

Source 6: EPF J002557.1-542320
R.A., Decl. (J2000) = 6.4879, -54.3890  deg 
Localization error radius = 10 arcsec 0.5-10 keV 
Flux = 1.48e-13 erg/cm^ 2/s 
Flux error = 5.01e-14 erg/cm^2/s (1 sigma) 
Separation = 8.0 arcmin

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).