The correlated variations of C IV narrow absorption lines and quasar
  continuum
  We assemble 207 variable quasars from the Sloan Digital Sky Survey, all with
at least 3 observations, to analyze C IV narrow absorption doublets, and obtain
328 C IV narrow absorption line systems. We find that 19 out of 328 C IV narrow
absorption line systems were changed by $\mid\Delta
W_r^{\lambda1548}\mid\ge3\sigma_{\Delta W_r^{\lambda1548}}$ on timescales from
15.9 to 1477 days at rest-frame. Among the 19 obviously variable C IV systems,
we find that (1) 14 systems have relative velocities $\upsilon_r>0.01c$ and 4
systems have $\upsilon_r>0.1c$, where $c$ is the speed of light; (2) 13 systems
are accompanied by other variable C IV systems; (3) 9 systems were changed
continuously during multiple observations; and (4) 1 system with $\upsilon_{\rm
r}=16~862$ km/s was enhanced by $\Delta W_r^{\lambda1548}=2.7\sigma_{\Delta
W_r^{\lambda1548}}$ in 0.67 day at rest-frame. The variations of absorption
lines are inversely correlated with the changes in the ionizing continuum. We
also find that large variations of C IV narrow absorption lines are difficult
to form on a short timescale.
