Open AccessIs the soft excess in active galactic nuclei real?
Author(s) -
Gierliński Marek,
Done Chris
Publication year - 2004
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2004.07687.x
Subject(s) - physics , opacity , astrophysics , active galactic nucleus , quasar , line (geometry) , spectral line , ionization , atomic physics , ion , astronomy , galaxy , optics , geometry , mathematics , quantum mechanics
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.