On the Covering Fraction Variability in an EUV Mini-BAL Outflow from PG 1206+459

TL;DR

This study reports the first detection of EUV absorption variability in a quasar's mini-BAL, attributing it to transverse motion of the absorbing gas, and discusses implications for AGN feedback.

Contribution

It presents the first observation of EUV mini-BAL variability and models the absorber's motion and location, highlighting its role in AGN feedback.

Findings

NeVIII absorption shows ~4 sigma variability over 2.8 months.

Covering fraction of NeVIII increased from 0.59 to 0.72.

Absorber likely located ~1.3 pc from the central engine.

Abstract

We report on the first detection of extreme-ultraviolet (EUV) absorption variability in the NeVIII 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 NeVIII doublet show a ~4 sigma variation over a timescale of 2.8 months in the QSO's rest-frame. Both members of the NeVIII doublet exhibit non-black saturation, indicating partial coverage of the continuum source. An increase in the NeVIII covering fraction from f_c = 0.59\pm0.05 to 0.72\pm0.03 is observed over the same period. The NeVIII 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 being the cause of the observed variability. Using a simple model of a transiting cloud we estimate a transverse speed of ~1800 km/s. For Keplerian motion, this corresponds to a distance between the absorber and the central engine of ~1.3 pc, which places the absorber just outside the BLR region. We further estimate a density of ~5\times10^6 cm^(-3) and a kinetic luminosity of ~10^43 - 10^44 erg/s. Such large kinetic powers suggest that outflows detected via EUV lines are potentially major contributors to AGN feedback.