ROSAT spectra of quasars

Details ROSAT spectra of quasars ROSAT spectra of quasars

Mar 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...295..309b&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 295, no. 2, p. 309-316

Astronomy and Astrophysics

Astronomy

13

Active Galactic Nuclei, Active Galaxies, Black Body Radiation, Bremsstrahlung, Quasars, X Ray Astronomy, X Ray Spectra, Interstellar Extinction, Red Shift, Rosat Mission

Scientific paper

X-ray observations of active galactic nuclei (AGN) with Einstein, European X-ray Observatory Satellite (EXOSAT) and Ginga have shown that the spectra of quasars in the energy range from 2 to 10 keV can be approximately described by a single power law model with a photon index of 1.7-2.0. They also suggested that a soft X-ray excess component (below approximately 1 keV) is a common feature in many quasars. In order to investigate the properties of the soft excess in radio-loud quasars we analysed the data of the pointed ROSAT/Position Sensitive Proportional Counter (PSPC) observations of the six radio-loud quasars PG 0007+106, PKS 0135-247, QSO 0537-286, QSO 0923+392, PG 1225+317, 3C 273. To these objects we added also the data of the radio-quiet quasar PG 0804+761. In four cases (including the radio-quiet object) we find that the spectra in the PSPC sensitivity band are considerably steeper than the spectra above 2 keV, a clear signature for a soft X-ray excess. In the other three objects the soft component could be hidden by the interstellar absorption or by the large redshift (z greater than 2) and can not be excluded. We point out the limits of the detectability of a soft component with the ROSAT/PSPC detector due to these effects. The comparison of different spectral models for the soft component (power law, thermal bremsstrahlung, black body) suggest that the soft component must decline very rapidly towards the higher energies.

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