TITLE:   GCN CIRCULAR
NUMBER:  44661
SUBJECT: GRB 260516D: EP-FXT follow-up observation
DATE:    26/05/17 10:45:05 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

Y.-H. I. Yin (HKU), Z.M. Wang (BNU), W.F. Wen (SZTU), Z.-X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team:

EP-FXT performed an automatic follow-up observation of GRB 260516D detected by SVOM/ECLAIRs (SVOM/sb26051616, Brunet et al., GCN 44649). The follow-up obervation started at 2026-05-16 22:46:58 UTC, approximately 2.1 hours after the SVOM trigger, with a total exposure time of 6080 s.

On-ground analysis of the FXT data found an uncatalogued fading source within the ECLAIRs error circle at R.A., Dec. = 233.8275, 6.5288 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). This position is consistent with the optical counterpart (Li et al., GCN 44654, Mohan et al., GCN 44655, Izzo et al., GCN 44656, García et al., GCN 44657, Wu et al., GCN 44659, Belkin et al., GCN 44660). The average FXT 0.3-10 keV spectrum can be fitted with an absorbed power-law model, with the Galactic hydrogen column density fixed at 4.71 x 10^20 cm^-2, an intrinsic hydrogen column density of 6.29 (-1.71/+1.71) x 10^21 cm^-2, and a photon index of 2.43 (-0.08/+0.08). The derived unabsorbed average flux in the 0.3-10 keV band is 3.99 (-0.14/+0.15) x 10^(-12) erg/s/cm^2.

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).