2025A&A...697A..79L

We present an analysis of the newly identified coordinated velocity shift signatures observed within two C IV broad absorption lines (BALs) in the quasar SDSS J093552.97+495314.3 (located at a redshift of z_em = 1.930). This particular quasar displays three distinct BAL systems, Systems A, B, and C. The coordinated velocity shifts in Systems A and B across two epochs of observations hint at potential accelerations within the outflows. Specifically, our findings reveal velocity shifts of approximately -1836 km s^–1 for System A and -547 km s^–1 for System B, occurring over a rest-frame time span of roughly 3.14 years. These shifts correspond to acceleration rates of -1.86 cm s^–2 and -0.55 cm s^–2, respectively. The concurrent occurrence of these velocity shifts among multiple components implies the presence of a unifying underlying mechanism. Additionally, these shifts are accompanied by variations in equivalent widths attributable to variations in the ionisation states of the clouds in response to changes in the ionising continuum. Based on these results, we postulate that the coordinated velocity shift signatures could be indicative of actual acceleration within the outflow clouds, driven primarily by radiation pressure emanating from the background light source.