2020ApJS..247...38X

We present a study of the BAL outflows seen in quasar SDSS J1042+1646 (z = 0.978) in the rest-frame 500-1050 Å (EUV500) region. The results are based on the analysis of recent Hubble Space Telescope/Cosmic Origins Spectrograph observations. Five outflow systems are identified, where, in total, they include ∼70 outflow troughs from ionic transitions. These include the first non-solar detections from transitions of O V*, Ne V*, Ar VI, Ca VI, Ca VII, and Ca VIII. The appearance of very high-ionization species (e.g., Ne VIII, Na IX, and Mg X) in all outflows necessitates at least two ionization phases for the observed outflows. We develop an interactive Synthetic Spectral Simulation method to fit the multitude of observed troughs. Detections of density sensitive troughs (e.g., S IV* λ661.40 Å and the O V* multiplet) allow us to determine the distance of the outflows (R) as well as their energetics. Two of the outflows are at R ≃ 800 pc and one is at R ≃ 15 pc. One of the outflows has the highest kinetic luminosity on record ({dot}E_k=5×10⁴⁶ erg s^–1), which is 20% of its Eddington luminosity. Such a large ratio suggests that this outflow can provide the energy needed for active galactic nucleus feedback mechanisms.