We report the kinematic shift of 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 km s ^ { -1 } that shows kinematic shift of 1166 \pm 65 km s ^ { -1 } , and a red component of system B at \sim 7000 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 sysetm B ) in J1208+0355 is ionization change scenario as 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 .
Secondly , we find line-locking phenomena from the blended NALs within system B , indicating that these outflow clouds are driven by 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 .