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Probing the hard X-ray properties of high-redshift Radio-Quiet Quasars with ASCA

C. Vignali·A. Comastri·M. Cappi·G. G. C. Palumbo·M. Matsuoka·H. Kubo
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Abstract

This paper reports the X-ray spectral analysis of 5 high-redshift (z \ge 2) radio-quiet quasars observed by ASCA. A simple power law continuum plus cold Galactic absorption model well fits all the spectra (tipically between $\sim$ 2-30 keV in the sources frame). Neither the X-ray spectral hardening, attributed to a reflection component and observed in Seyfert galaxies, nor the excess absorption previously detected in high-redshift radio-loud quasars, have been revealed. Only a marginal evidence of a neutral or mildly ionized FeKαline is found in one of the quasars. The average spectral slope in the observed 0.7--10 keV energy range, $<Γ> = 1.67 \pm{0.11}$ (dispersion $σ\sim 0.07$), appears to be flatter than that of low-z radio-quiet quasars ($Γ\simeq 1.9-2$) and slightly steeper, but consistent with $Γ$ = 1.61 \pm{0.04} (σ\sim 0.10)$ of high-z radio-loud quasars.

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C. Vignali, A. Comastri, M. Cappi, G. G. C. Palumbo, M. Matsuoka, H. Kubo. 1998-12-09. Probing the hard X-ray properties of high-redshift Radio-Quiet Quasars with ASCA. https://doi.org/10.1086/307141

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