TITLE:   GCN CIRCULAR
NUMBER:  44976
SUBJECT: EP260616a/GRB 260616B: EP-FXT follow-up observation
DATE:    26/06/18 10:37:23 GMT
FROM:    EP Team at NAOC/CAS <ep_ta@bao.ac.cn>

D. Y. Li, T. Y. Liu (NAO, CAS), J. H. WU(GZHU), Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe team

EP-FXT performed a follow-up observation of EP260616a/GRB 260616B (Li et al., GCN 44956; Preis & Greiner, GCN 44951; Malacaria et al., GCN 44953; Asaoka et al., GCN 44966) about 25.5 hours after the WXT detection, with an exposure time of 6.2 ks. An uncatalogued source was detected within the WXT error circle at R.A. = 256.0839, DEC = -32.3007 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT spectrum can be fitted with an absorbed powerlaw with a hydrogen column density fixed at the Galactic value of 3.4 x 10^21 cm^-2 and a photon index of 1.62 (+0.27, -0.26). The derived unabsorbed 0.5-10 keV flux is approximately 8.7 (+2.2, -1.7) x 10^-13 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.

No optical counterpart have been detected (Mandarakas et al., GCN 44965). Further EP-FXT follow-up observations will be arranged.

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).