AstroNote 2026-38

The Follow-up X-ray Telescope on board the Einstein Probe conducted a 5ks observation at the position of AT2026dbl (Wise et al.; AstroNote 2026-36) beginning at UTC 2026-02-18T17:57:32. An uncatalogued X-ray source was detected at R.A. = 135.3221, DEC = 18.6029 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic), consistent with the optical position. 

We performed a preliminary analysis of the FXT spectrum in the 0.5-10 keV energy range. We fit this with an absorbed power-law with a line-of-sight hydrogen column density of 3.19 x 10^20 cm^-2 (calculated using the nh utility). We find a photon index of 2.5 ± 0.6, with an unabsorbed flux of 5.9 (+1.6/-1.2) x 10^-14 erg/s/cm^2. Uncertainties in these parameters are reported at the 90% C.L. More detailed analysis is ongoing.

This flux measurement would correspond to a luminosity at the redshift of AT2026dbl (z = 0.19; Wise et al., AstroNote 2026-36) of 6.4 (+1.7/-1.3) x 10^42 erg/s, which is similar to the early-time X-ray flux of other LFBOTs such as AT2018cow at a similar epoch (Margutti et al. 2019). We encourage additional multiwavelength follow-up.

The Einstein Probe is a space mission supported by the Strategic Priority Program on Space Sciénce of the Chinese Academy of Sciences, in collaboration with the European Space Agency, the Max-Planck-Institute for Extraterrestrial Physics (Germany), and the Centre National d'études Spatiales (France).