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Astron. Astrophys. 362, 69-74 (2000)

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5. Conclusions

The most important results obtained from the BeppoSAX observation of the luminous quasar PDS 456 can be summarized as follows:

  • The BeppoSAX observation confirms the presence of a deep ionized K edge discovered by RXTE at [FORMULA] 8.5-9 keV implying the presence of highly ionized gas around the central source.

  • The absence of significant iron line emission in both the BeppoSAX and ASCA data favours a model where the hard X-ray continuum is absorbed by a high column density of highly ionized gas. Further spectral complexity is present at lower energies, requiring the presence of an additional cold (or weakly ionized) absorber.

  • The high luminosity of PDS 456 ([FORMULA] [FORMULA] 1047 erg s-1) and the properties of the absorbing medium which partially hides the X-ray source make this object a good candidate to test the emission mechanisms and reprocessing in quasars.

Further investigations with CHANDRA and XMM would be extremely helpful to assess the nature of the X-ray emission (both in the soft and in hard X-rays domain) and the ionization state of the absorbing matter. Moreover, X-ray spectroscopy of others bright, relatively nearby quasars would be very important to check whether PDS 456 is an exceptional object or the imprints of highly ionized high column density gas are common in luminous quasars. A better knowledge of the X-ray properties of bright AGN would also allow to probe the physics of accretion processes at high luminosities.

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© European Southern Observatory (ESO) 2000

Online publication: October 30, 19100