We report on the first detection of extreme-ultraviolet ( EUV ) absorption variability in the Ne viii \lambda \lambda 770,780 mini-broad absorption line ( mini-BAL ) in the spectrum of the quasar ( QSO ) PG 1206+459 .
The observed equivalent width ( EW ) of the Ne viii doublet shows a \sim 4 \sigma variation over a timescale of 2.8 months in the QSO ’ s rest-frame .
Both members of the Ne viii doublet exhibit non-black saturation , indicating partial coverage of the continuum source .
An increase in the Ne viii covering fraction from f _ { c } = 0.59 \pm 0.05 to 0.72 \pm 0.03 is observed over the same period .
The Ne viii profiles are too highly saturated to be susceptible to changes in the ionization state of the absorbing gas .
In fact , we do not observe any significant variation in the EW and / or column density after correcting the spectra for partial coverage .
We , thus , propose transverse motions of the absorbing gas as the cause of the observed variability .
Using a simple model of a transiting cloud we estimate a transverse speed of \sim 1800 km s ^ { -1 } .
For Keplerian motion , this corresponds to a distance between the absorber and the central engine of \sim 1.3 pc , which places the absorber just outside the broad-line region .
We further estimate a density of \sim 5 \times 10 ^ { 6 } cm ^ { -3 } and a kinetic luminosity of \sim 10 ^ { 43 } – 10 ^ { 44 } erg s ^ { -1 } .
Such large kinetic powers suggest that outflows detected via EUV lines are potentially major contributors to AGN feedback .