• K. Bensch

      Articles written in Journal of Astrophysics and Astronomy

    • Measures of the Soft X-ray Excess as an Eigenvector 1 Parameter for Active Galactic Nuclei

      K. Bensch A. del Olmo J. Sulentic J. Perea P. Marziani

      More Details Abstract Fulltext PDF

      We present a preliminary analysis of X-ray data of quasars in the context of the 4D eigenvector 1 parameter space (Sulentic et al. 2000a, b). 4DE1 serves as a surrogate H-R diagram for representing empirical diversity among quasars and identifying the physical drivers of the diversity. The soft X-ray spectral index (𝛤soft) was adopted as one of the key 4DE1 that correlates contrasting extremes in Type 1 properties. 4DE1 motivated the hypothesis of two quasar populations (A and B) divided by 𝐿/𝐿EDD ≈ 0.2. Pop. A is a largely radio-quiet population with FWHM 𝐻𝛽 < 4000 km/s and often showing a soft X-ray excess. Pop. B is a mix of radio-quiet and a majority of RL quasars shows only a hard X-ray power-law SED. The X-ray separation was based upon earlier ROSAT and ASCA data but we now confirm this dichotomy with large samples of X-ray spectra obtained with XMM-Newton and SWIFT. One popular idea connects the soft excess in Pop. A quasars as a signature of thermal emission from a hot accretion disk in sources radiating close to the Eddington limit.

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