2025ApJ...984...62L

We present a rare signature of reacceleration in a C IV broad absorption line (BAL) of the quasar SDSS J083817.00+295526.5. This quasar showcases three distinct BAL systems, labeled as systems A, B, and C. Notably, system A, which boasts the highest velocity of ∼-22,000 km s^–1, initially demonstrates a deceleration of ∼3160 km s^–1 in its C IV ion over a rest-frame period of ∼2.3 yr. Subsequently, it exhibits an acceleration of ∼-3366 km s^–1 over a rest-frame period of ∼2.6 yr. To elucidate the nature of these signatures, we conducted a thorough analysis, focusing on the ionization state, location, and variation situation of the three BAL systems. Our findings reveal that system A exhibits higher velocities, higher ionization states, and is situated closer to the central source compared to systems B and C. Collectively, these characteristics suggest that the outflow generating system A is located in an exceptionally extreme environment and experiences more pronounced impacts from background radiation energy than systems B and C. Given the currently limited observational data, the physical origin of this peculiar reacceleration phenomenon remains an open question. We briefly discuss several possibilities and hypothesize that the outflow winds initially interact with ambient galactic material, causing their deceleration, and are subsequently reaccelerated by the radiation pressure from the central source.