Ultraviolet Continuum of the Quasar PKS 0405-123: Lyman Edge in the Accretion Disk Spectrum

Details Ultraviolet Continuum of the Quasar PKS 0405-123: Lyman Edge in the Accretion Disk Spectrum Ultraviolet Continuum of the Quasar PKS 0405-123: Lyman Edge in the Accretion Disk Spectrum

May 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aas...186.2404l&link_type=abstract

American Astronomical Society, 186th AAS Meeting, #24.04; Bulletin of the American Astronomical Society, Vol. 27, p.846

Astronomy and Astrophysics

Astronomy

1

Scientific paper

We study the characteristics of the ultraviolet continuum of the quasar PKS 0405-123 using the archival HST/FOS spectrum. The spectrum from 1150 to 3300 Angstroms shows a steeply rising continuum in F_λ with a strong absorption feature ~ 100 Angstroms wide around the intrinsic Lyman limit of this z=0.574 quasar. The spectrum also shows Lyman absorption line systems in the wavelength range of the broad absorption feature. A Lyalpha absorption line whose corresponding Lyman limit could contribute to the broad absorption feature is also identified. We investigate the possibility that the broad absorption feature may be due to the sum of the contributions from each Lyman absorption system. The estimated opacity due to the Lyman absorption systems in the region of the broad absorption feature, however, is not high enough to completely account for it. We thus propose that a significant part of the continuum drop in the broad absorption feature may be due to a broadened Lyman edge in the spectrum of an accretion disk. We model the ultraviolet continuum using an alpha -disk with an adiabatic vertical structure. We compute the emitted spectrum by solving the radiative transfer numerically. The observed spectrum is corrected for relativistic effects assuming a Schwarzschild metric, and we also consider the effect of Comptonization by a surrounding hot corona on the observed spectrum. A realistic disk spectrum with a significant amount of Comptonization describes the steep continuum shape and the broad Lyman edge feature, and it is consistent with the X-ray flux observed with EINSTEIN observatory IPC. This work was supported by NASA Grant NAG 5-1630 to the FOS team and NASA contract NAS 5-27000 to the Johns Hopkins University.

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