TITLE:   GCN CIRCULAR
NUMBER:  43927
SUBJECT: GRB 260228A: further EP-FXT observations and X-ray afterglow confirmation
DATE:    26/03/05 19:04:24 GMT
FROM:    SVOM_group <svomgroup@bao.ac.cn>

A. Saccardi (CEA/Irfu), Y. Julakanti (Univ. Leicester), D. Turpin (CEA/Irfu), J.-L. Atteia (IRAP), D. B. Malesani (DAWN/NBI and Radboud), Y. H. Cheng (SWIFAR, YNU), R. A. J. Eyles-Ferris (Univ. Leicester) report on behalf of the SVOM and Einstein Probe teams:

We performed a second observation at the location of the SVOM/ECLAIRs GRB 260228A (Julakanti et al., GCN 43882) with the Follow-up X-ray Telescope (FXT) on board the Einstein Probe (EP) mission. The observation started on 2026-03-04 at 19:25:58 UT (3.94 days after the trigger) with a total exposure time of ~6000 s.

All six sources detected by EP/FXT during the first visit (Cheng et al., GCN 43900) are detected in the second epoch data set. The brightest of them (EPF_J155124.0+262035; error radius of 10 arcsec) has faded by a factor of ~10, down to a flux of (1.92 +/- 0.47) x 10^-13 erg/s/cm^-2 (0.5-10 keV; 1-sigma uncertainty).

The fading behavior of this X-ray source confirms it as the afterglow of GRB 260228A.

The early deep optical limits measured by SVOM/VT (Li et al., GCN 43886), compared to the bright X-ray flux (Cheng et al., GCN 43900), suggest that this could be a dark GRB.

We encourage multi-wavelength follow-up observation of this source.

​​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).