2025A&A...694A.217L

We present the observation of a velocity shift in the broad absorption line (BAL) of C IV ion in quasar SDSS J145229.08+093204.9 (hereafter J1452+0932).This quasar exhibits three distinct BAL systems, designated as systems A, B, and C. Notably, system A, which possesses the highest velocity of approximately -23 000 km s^–1, demonstrates a velocity shift of -1097 km s^–1 in its C IV ion over a rest-frame period of approximately 1.7 years. To elucidate the nature of these variations, we conducted a comprehensive analysis focusing on the variation situation, location, ionisation state, and profile shape of the three BAL systems in J1452+0932. Our findings reveal that system A is situated closer to the central source compared to systems B and C. Furthermore, system A exhibits higher velocities, higher ionisation states, and smoother profile morphologies. These characteristics collectively suggest that the outflow generating system A is situated in a particularly extreme environment and experiences more pronounced impacts from background radiation energy than systems B and C. Consequently, we postulate that the observed velocity shift in system A may signify an actual line-of-sight acceleration of the outflow, induced by the radiation pressure emanating from the central source. Specifically, this scenario could occur if our line of sight intersects an outflow at a location where it is undergoing acceleration towards its terminal outflow velocity, or if a previously coasting outflow is undergoing renewed acceleration.