Abstract:
We report the kinematic shift and strength variability of the C IV broad absorption-line
(BAL) trough in two high-ionization X-ray-bright quasi-stellar objects (QSOs): SDSS
J085551+375752 (at zem ∼ 1.936) and SDSS J091127+055054 (at zem ∼ 2.793). Both
these QSOs have shown a combination of profile shifts and the appearance and disappearance
of absorption components belonging to a single BAL trough. The observed average kinematic
shift of the whole BAL profile resulted in an average deceleration of ∼−0.7 ± 0.1,
−2.0 ± 0.1 cm s⁻² over rest-frame time-spans of 3.11 and 2.34 yr for SDSS J085551+375752
and SDSS J091127+055054, respectively. To our knowledge, these are the largest kinematic
shifts known, exceeding by factors of about 2.8 and 7.8 the highest deceleration reported in
the literature; this makes both objects potential candidates to investigate outflows using multiwavelength monitoring of their line and continuum variability. We explore various possible
mechanisms to understand the observed profile variations. Outflow models involving many
small self-shielded clouds, probably moving in a curved path, provide the simplest explanation
for the C IV BAL strength and velocity variations, along with the X-ray-bright nature of these
sources.
