We have observed a dramatic change in the spectrum of the formerly heavily absorbed ‘ overlapping-trough ’ iron low-ionization broad absorption line ( FeLoBAL ) quasar FBQS J1408+3054 .
Over a time span of between 0.6 to 5 rest-frame years , the Mg ii trough outflowing at 12,000 km s ^ { -1 } decreased in equivalent width by a factor of two and the Fe ii troughs at the same velocity disappeared .
The most likely explanation for the variability is that a structure in the BAL outflow moved out of our line of sight to the ultraviolet continuum emitting region of the quasar ’ s accretion disk .
Given the size of that region , this structure must have a transverse velocity of between 2600 km s ^ { -1 } and 22,000 km s ^ { -1 } .
In the context of a simple outflow model , we show that this BAL structure is located between approximately 5800 and 46,000 Schwarzschild radii from the black hole .
That distance corresponds to 1.7 to 14 pc , 11 to 88 times farther from the black hole than the H \beta broad-line region .
The high velocities and the parsec-scale distance for at least this one FeLoBAL outflow mean that not all FeLoBAL outflows can be associated with galaxy-scale outflows in ultraluminous infrared galaxies transitioning to unobscured quasars .
The change of FBQS J1408+3054 from an FeLoBAL to a LoBAL quasar also means that if ( some ) FeLoBAL quasars have multiwavelength properties which distinguish them from HiBAL quasars , then some LoBAL quasars will share those properties .
Finally , we extend previous work on how multiple-epoch spectroscopy of BAL and non-BAL quasars can be used to constrain the average lifetime of BAL episodes ( currently > 60 rest-frame years at 90 % confidence ) .