GCN Circular 44337
Subject
EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
Event
Date
2026-04-18T08:34:24Z (a day ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
K. R. Ni (CCNU), Y. L. Wang (NAO, CAS; ICE, CSIC), Y. Q. Zhao (USTC; PRIC) and Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team:
The X-ray transient EP260417a was detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Wang et al., GCN 44325) at 2026-04-17 00:23:02 (UTC). The average WXT 0.5-4 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 1.32 × 10^21 cm^-2, and a photon index of 0.78 (+/-0.27). The derived average unabsorbed 0.5-4 keV flux is 1.57 (+0.49/-0.39) × 10^(-10) erg/s/cm^2.
Follow-up observation by the Follow-up X-ray Telescope (FXT) on board EP was performed at 2026-04-17T14:24:17 (UTC), ~14 hours after the WXT detection. The exposure time of the observation is around 3 ks. The on-ground analysis of the FXT data found an uncatalogued source at R.A. = 245.3232, DEC = -22.0249 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT light curve shows no significant variability. The average FXT 0.5-10 keV spectra can be fitted with an absorbed power-law with a free hydrogen column density of 1.54 (+/-0.4) × 10^21 cm^-2, and a photon index of 1.68 (+/-0.13). The derived average unabsorbed 0.5-10 keV flux is 7.79 (-0.76/+0.89) × 10^(-12) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
We note that the X-ray position determined from EP/FXT observation is ~6.6 degrees away from that of GRB 260417A, which is RA = 252.0, Dec = -19.8 (J2000) with a statistical uncertainty of 3.4 degrees, as reported by the Fermi GBM team (GCN 44317). The detection in X-rays by WXT was ~13 minutes later than the reported GBM detection time of GRB 260417A. Therefore it is possible that GRB 260417A is the Gamma-ray counterpart of EP260417a.
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).