  Extremely variable quasars can also show strong changes in broad-line
emission strength and are known as changing-look quasars (CLQs). To study the
CLQ transition mechanism, we present a pilot sample of CLQs with X-ray
observations in both the bright and faint states. From a sample of quasars with
bright-state archival SDSS spectra and (Chandra or XMM-Newton) X-ray data, we
identified five new CLQs via optical spectroscopic follow-up, and then obtained
new target-of-opportunity X-ray observations with Chandra. No strong absorption
is detected in either the bright- or the faint-state X-ray spectra. The
intrinsic X-ray flux generally changes along with the optical variability, and
the X-ray power-law slope becomes harder in the faint state. Large amplitude
mid-infrared variability is detected in all five CLQs, and the MIR variability
echoes the variability in the optical with a time lag expected from the
light-crossing time of the dusty torus for CLQs with robust lag measurements.
The changing-obscuration model is not consistent with the observed X-ray
spectra and spectral energy distribution changes seen in these CLQs. It is
highly likely that the observed changes are due to the changing accretion rate
of the supermassive black hole, so the multiwavelength emission varies
accordingly, with promising analogies to the accretion states of X-ray
binaries.

Astrophysics of Galaxies;High Energy Astrophysical Phenomena