The nature of associated absorption and the ultraviolet-x-ray connection in 3C 288.1

We discuss new Hubble Space Telescope spectroscopy of the radio-loud quasar 3C 288.1. The data cover ∼590 to ∼1610 Å in the quasar rest frame. They reveal a wealth of associated absorption lines (AALs) with no accompanying Lyman-limit absorption. The metallic AALs range in ionization from C III and N III to Ne VIII and Mg x. We use these data and photoionization models to derive the following properties of the AAL gas: (1) There are multiple ionization zones within the AAL region, spanning a factor of at least ∼50 in ionization parameter. (2) The overall ionization is consistent with the "warm" X-ray continuum absorbers measured in Seyfert 1 nuclei and other QSOs. (3) However, the column densities implied by the AALs in 3C 288.1 are too low to produce significant bound-free absorption at any UV-X-ray wavelengths. Substantial X-ray absorption would require yet another zone, having a much higher ionization or a much lower velocity dispersion than the main AAL region. (4) The total hydrogen column density in the AAL gas is log N_H(cm^-2) ≈ 20.2 (5) The metallicity is roughly half solar. (6) The AALs have deconvolved widths of ∼900 km s^-1, and their centroids are consistent with no shift from the quasar systemic velocity (conservatively, within ± 1000 km s^-1). (7) There are no direct indicators of the absorber's location in our data, but the high ionization and high metallicity both suggest a close physical relationship to the quasar/host galaxy environment. Finally, the UV continuum shape gives no indication of a "blue bump" at higher energies. There is a distinct break of unknown origin at ∼1030 Å, and the decline toward higher energies (with spectral index α ≈ -1.73, for f_v ∝ v^α) is even steeper than a single power-law interpolation from 1030 Å to soft X-rays.