X-ray and multi-epoch optical/UV investigations of BAL to non-BAL quasar
  transformations
  We report on an X-ray and optical/UV study of eight Broad Absorption Line
(BAL) to non-BAL transforming quasars at $z\,\approx\,$1.7-2.2 over 0.29-4.95
rest-frame years with at least three spectroscopic epochs for each quasar from
the SDSS, BOSS, $Gemini$, and ARC 3.5-m telescopes. New $Chandra$ observations
obtained for these objects show their values of $\alpha_{\rm ox}$ and
$\Delta{\alpha}_{\rm ox}$, as well as their spectral energy distributions, are
consistent with those of non-BAL quasars. Moreover, our targets have X-ray
spectral shapes that are, on average, consistent with weakened absorption with
an effective power-law photon index of $\Gamma_{\rm
eff}\,=\,1.69^{+0.25}_{-0.25}$. The newer $Gemini$ and ARC 3.5-m spectra reveal
that the BAL troughs have remained absent since the BOSS observations where the
BAL disappearance was discovered. The X-ray and optical/UV results in tandem
are consistent with at least the X-ray absorbing material moving out of the
line-of-sight, leaving an X-ray unabsorbed non-BAL quasar. The UV absorber
might have become more highly ionized (in a shielding-gas scenario) or also
moved out of the line-of-sight (in a wind-clumping scenario).
