rather than with the HST images.

The low number of detected photons limits significantly the spectral constraints that can be obtained from the X-ray analysis; however, to provide basic information for both sources, we fitted their spectra, extracted from the data, using simple models (within [xspec]{} v.12.9, Arnaud et al. 1996) and the Cash statistics (Cash 1979), which is appropriate for low-count spectra.

Fitting SDP.9 spectrum with a powerlaw provides $\Gamma=1.1\pm{1.0}$, suggestive of obscuration. If we fix $\Gamma$ to 1.8, as typically observed in AGN and quasars (e.g., Piconcelli et al. 2005), we obtain a column density of $\approx5.2\times10^{22}$ cm$^{-2}$ at the source redshift (3$\sigma$ upper limit of $\approx3.3\times10^{23}$ cm$^{-2}$). The observed 2–10 keV flux is $\approx3.6\times10^{-15}$ [${\rm erg~cm}^{-2}~{\rm s}^{-1}$]{}, and the derived, apparent rest-frame 2–10 keV luminosity (corrected for the absorption but not for the magnification) is $\approx3.7\times10^{43}$ [erg s$^{-1}$]{}. The faint flux of SDP.9 explains why the source was undetected (with an upper limit of $\approx10^{-14}$ [${\rm erg~cm}^{-2}~{\rm s}^{-1}$]{} in the 0.5–8 keV band) in the XMM-ATLAS survey (Ranalli et al. 2015), that covers a 6 deg$^2$ area with a 3 ks average exposure. The non-detection of the AGN in  is suggestive of the presence of obscuration, with 