Compton reflection and the variable X-ray spectrum of NGC 5548

Details Compton reflection and the variable X-ray spectrum of NGC 5548 Compton reflection and the variable X-ray spectrum of NGC 5548

Feb 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991mnras.248..760n&link_type=abstract

Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 248, Feb. 15, 1991, p. 760-772.

Astronomy and Astrophysics

Astronomy

96

Astronomical Spectroscopy, Compton Effect, Seyfert Galaxies, Spaceborne Astronomy, X Ray Spectra, Astronomical Models, Emission Spectra, Exosat Satellite, Light Curve, Metallicity, Spectrum Analysis

Scientific paper

Spectral analysis of EXOSAT and Ginga observations of the Seyfert galaxy NGC 5548 has revealed a complex spectral form. At least four components, a steep nonthermal power law, an iron line, a 'hard tail' and a soft emission component, have been identified in the 0.05-20 keV range. The soft component arises from thermal emission by optically thick material. Hard X-ray illumination of this material gives rise to the hard tail, by continuum Compton reflection, and the bulk of the iron line, via fluorescence. Varying relative levels of the power law and reflected continua result in apparent spectral index variations. Spectral and temporal considerations lead to the conclusion that the material lies close to the central energy source. A region of highly ionized gas also contributes to the observed features, and changes in the ionization state of this material cause both variations in the measured low-energy column density and the relative amplitudes of hard and soft X-ray variability. The fact that the intrinsic power-law index of NGC 5548, at about 1.9, is steeper than the 'canonical' index of 1.7, has important consequences, both for emission models and spectral modeling of Seyfert type AGN.

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