Optical Variability Properties of Mini-BAL and NAL Quasars
  While narrow absorption lines (NALs) are relatively stable, broad absorption
lines (BALs) and mini-BAL systems usually show violent time variability within
a few years via a mechanism that is not yet understood. In this study, we
examine variable ionization state (VIS) scenario as a plausible mechanism, as
previously suspected. Over three years, we performed photometric monitoring
observations of four mini-BAL and five NAL quasars at $z_{\rm em}$ $\sim$ 2.0 -
3.1 using the 105 cm Kiso Schmidt Telescope in $u$, $g$, and $i$-bands. We also
performed spectroscopic monitoring observation of one of our mini-BAL quasar
(HS1603+3820) using the 188-cm Okayama Telescope over the same period as the
photometric observations. Our main results are as follows: (1) Structure
function (SF) analysis revealed that the quasar UV flux variability over three
years was not large enough to support the VIS scenario, unless the ionization
condition of outflow gas is very low. (2) There was no crucial difference
between the SFs of mini-BAL and NAL quasars. (3) The variability of the
mini-BAL and quasar light curves was weakly synchronized with a small time
delay for HS1603+3820. These results suggest that the VIS scenario may need
additional mechanisms such as a variable shielding by X-ray warm absorbers.
