A Kinematic Shift of the C IV Broad Absorption Line in Quasar SDSS
  J120819.29+035559.4
  We report the kinematic shift of the C IV broad absorption line (BAL) in
quasar SDSS J120819.29+035559.4 (hereafter J1208+0355). This quasar shows two
BAL systems, including a blue component of system A at $\sim$-23500$\,\rm
km\,s^{-1}$ that shows a kinematic shift of -1166$\pm$65$\,\rm km\,s^{-1}$, and
a red component of system B at $\sim$-7000$\,\rm km\,s^{-1}$ that can be
decomposed into several narrow absorption lines (NALs). First, we confirm that
the most likely cause for the equivalent width variations of the absorption
lines (at least for system B) in J1208+0355 is the ionization change scenario
as a response to the changes in the ionization continuum according to the
following observational factors: (1) coordinated multiple absorption lines
strengthening; (2) the continuum flux shows an obvious weakening. Second, we
find line-locking phenomena from the blended NALs within system B, indicating
that these outflow clouds are driven by a radiative force caused by resonance
lines. The above two research aspects convincingly reveal that the BAL outflows
of J1208+0355 are affected by the background radiation energy. Therefore, we
infer that the kinematic shift shown in system A may be produced by actual
line-of-sight acceleration of the outflow clouds, which is driven by radiation
pressure from the background light source.
