X-raying winds in distant quasars: the first high-redshift wind duty
  cycle
  Theoretical models of wind-driven feedback from Active Galactic Nuclei (AGN)
often identify Ultra-fast outflows (UFOs) as being the main cause for
generating galaxy-size outflows, possibly the main actors in establishing the
so-called AGN-galaxy co-evolution. UFOs are well characterized in local AGN but
much less is known in quasars at the cosmic time when SF and AGN activity
peaked ($z\simeq1-3$). It is therefore mandatory to search for evidences of
UFOs in high-$z$ sources to test the wind-driven AGN feedback models. Here we
present a study of Q2237+030, the Einstein Cross, a quadruply-imaged
radio-quiet lensed quasar located at $z=1.695$. We performed a systematic and
comprehensive temporally and spatially resolved X-ray spectral analysis of all
the available Chandra and XMM-Newton data (as of September 2019). We find clear
evidence for spectral variability, possibly due to absorption column density
(or covering fraction) variability intrinsic to the source. We detect, for the
first time in this quasar, a fast X-ray wind outflowing at $v_{\rm
out}\simeq0.1c$ that would be powerful enough ($\dot{E}_{\rm kin}\simeq0.1
L_{\rm bol}$) to significantly affect the host galaxy evolution. We report also
on the possible presence of an even faster component of the wind ($v_{\rm
out}\sim0.5c$). Given the large sample and long time interval spanned by the
analyzed X-ray data, we are able to roughly estimate, for the first time in a
high-$z$ quasar, the wind duty cycle as $\approx0.46\,(0.31)$ at $90\%\,(95\%)$
confidence level. Finally, we also confirm the presence of a Fe K$\alpha$
emission line with variable energy, which we discuss in the light of
microlensing effects as well as considering our findings on the source.
