Previous abstract Next abstract

Session 103 - Quasars & Blazars.
Display session, Saturday, January 10
Exhibit Hall,

[103.09] Why Do Soft X-Rays Weaken With Increasing QSO Luminosity?

P. J. Green (SAO)

As far back as 1980, it was known that optically-selected QSOs show a decrease in their X-ray emission relative to optical as a function of luminosity. Is this trend the result of a softening of the intrinsic spectral energy distribution (SED) as a function of luminosity, or an effect extrinsic to the energy production mechanism?

Intrinsic absorption lines in UV spectra of QSOs range from narrow line associated absorbers to deep, broad absorption lines, spanning up to 2 orders of magnitude in equivalent width. Recent results from the ROSAT All Sky Survey, and from deep ROSAT pointings reveal that broad absorption line quasars (BALQSOs) are weak in the soft X-ray bandpass (\alpha_ox>1.8) in comparison to QSOs with normal optical/UV spectra (øverline\alpha_ox=1.4). Less spectacular UV absorbers show significant soft X-ray absorption as well.

Could X-ray faintness in QSOs largely be caused by the same absorbers producing the apparent UV absorption? Is it possible that the \alpha_ox(L_opt) correlation is itself caused by absorption? This hypothesis can already be at least weakly tested by 1) excluding known BALs from a large optical/X-ray sample and 2) removing QSOs with any known absorption. Our results are consistent with, but put no strong constraints on the hypothesis that the weakening of soft X-rays with luminosity are due to absorption. We note that if at least some of the correlation is caused by increased warm absorption at higher luminosities, then it should weaken in soft X-ray selected samples.

Program listing for Saturday