Observations and models of the UV/soft X-ray spectrum of the quasar PG 1116+215.

Details Observations and models of the UV/soft X-ray spectrum of the quasar PG 1116+215. Observations and models of the UV/soft X-ray spectrum of the quasar PG 1116+215.

Jan 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...293..641u&link_type=abstract

Astronomy and Astrophysics 293, 641-651 (1995)

Astronomy and Astrophysics

Astrophysics

5

Quasars: Pg 1116+215, Accretion, Accretion Disks, X-Rays: Galaxies

Scientific paper

The radio quiet quasar PG 1116+215 has been observed four times with the ROSAT-PSPC, once during the All-Sky Survey and three times in pointed observations including one lasting 24320 seconds (25300 counts). Contemporaneous IUE observations were secured for two of the pointed observations. Overall the PSPC spectra at all 4 epochs can be reasonably well represented by a power law and galactic N_H_. The slope {GAMMA}~2.7 is the same in May 1993 as at the other epochs while the count rate on that date is 1.5 times larger. Comptonisation of the UV photons by energetic electrons is a possible mechanism to re-shape the high energy end of the thermal component into a power law. However, since comptonization is also invoked to produce the medium/hard X-ray component ({GAMMA}=1.9) it would be difficult to produce also by comptonization a second power law component with a different photon index. The analysis of the PSPC spectra shows that the only spectral change detected among the four observations is a hardening of the high energy part of the spectrum in December 1992. This is suggestive of and consistent with the emergence at that epoch of a hard component similar to the one commonly seen in the Ginga spectra of Seyferts and radio quiet quasars. For this reason, we have compared the PSPC spectra with two-component models: power law + thermal component (black body, bremsstrahlung, or inner disk of an accretion disk). In all cases the interpolation of the models fails by a factor of at least 10 to reproduce the UV spectrum. We have also attempted to model the entire PSPC-IUE spectra of June 1991 and May 1993 with 2 two-component models, both including a power law component with {GAMMA}=1.9. The other component is either the radiation dominated inner part of an accretion disk, or the emission of a slab irradiated by a central hard X-ray source. Both models reproduce the general UV/soft X-ray ratio but fail to give an acceptable fit of the soft X-ray spectrum. In this and other quasars the flux from the irradiating component (the medium-hard X-ray component with {GAMMA}=1.9) extrapolated to 100 keV is more than 10 times smaller than the flux from the irradiated disk. This energy budget problem is alleviated if the X-ray source is anisotropic and emits preferentially towards the disk.

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