The destruction and recreation of the X-ray corona in a changing-look
  Active Galactic Nucleus
  We present the drastic transformation of the X-ray properties of the active
galactic nucleus 1ES 1927+654, following a changing-look event. After the
optical/UV outburst the power-law component, produced in the X-ray corona,
disappeared, and the spectrum of 1ES 1927+65 instead became dominated by a
blackbody component ($kT\sim 80-120$ eV). This implies that the X-ray corona,
ubiquitously found in AGN, was destroyed in the event. Our dense $\sim 450$ day
long X-ray monitoring shows that the source is extremely variable in the X-ray
band. On long time scales the source varies up to $\sim 4$ dex in $\sim 100$
days, while on short timescales up to $\sim2$ dex in $\sim 8$ hours. The
luminosity of the source is found to first show a strong dip down to $\sim
10^{40}\rm\,erg\,s^{-1}$, and then a constant increase in luminosity to levels
exceeding the pre-outburst level $\gtrsim $300 days after the optical event
detection, rising up asymptotically to $\sim 2\times10^{44}\rm\,erg\,s^{-1}$.
As the X-ray luminosity of the source increases, the X-ray corona is recreated,
and a very steep power-law component ($\Gamma\simeq 3$) reappears, and
dominates the emission for 0.3-2 keV luminosities $\gtrsim
10^{43.7}\rm\,erg\,s^{-1}$, $\sim 300$ days after the beginning of the event.
We discuss possible origins of this event, and speculate that our observations
could be explained by the interaction between the accretion flow and debris
from a tidally disrupted star. Our results show that changing-look events can
be associated with dramatic and rapid transformations of the innermost regions
of accreting SMBHs.
