Is the soft excess in active galactic nuclei real?

Marek Gierliński (Lead / Corresponding author), Chris Done

Research output: Contribution to journalArticlepeer-review

359 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)L7-L11
Number of pages5
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Publication statusPublished - 21 Mar 2004


  • Accretion, accretion discs
  • Atomic processes
  • X-rays: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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