Is the soft excess in active galactic nuclei real?
Abstract
We systematically analyse all publicly available XMM-Newton spectra of radio-quiet PG quasars. The soft X-ray excess in these objects is well modelled by an additional, cool, Compton scattering region. However, the remarkably constant temperature derived for this component over the whole sample requires a puzzling fine tuning of the parameters. Instead, we propose that the soft excess is an artifact of strong, relativistically smeared, partially ionized absorption. The strong jump in opacity at ~0.7 keV from O VII, O VIII and iron can lead to an apparent soft excess below this energy, which is trivially constant since it depends on atomic processes. This can have a dramatic effect on the derived spectrum, which has implications for fitting the relativistic smearing of the reflected iron line emission from the disc.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- March 2004
- DOI:
- 10.1111/j.1365-2966.2004.07687.x
- arXiv:
- arXiv:astro-ph/0312271
- Bibcode:
- 2004MNRAS.349L...7G
- Keywords:
-
- accretion;
- accretion discs;
- atomic processes;
- X-rays: galaxies;
- Astrophysics
- E-Print:
- Accepted for publication in MNRAS