%0 Generic %1 nanni2017properties %A Nanni, R. %A Vignali, C. %A Gilli, R. %A Moretti, A. %A Brandt, W. N. %D 2017 %K high-z quasars x-ray %T The X-ray properties of z$\sim$6 luminous quasars %U http://arxiv.org/abs/1704.08693 %X We present a systematic analysis of X-ray archival data of all the 29 quasars (QSOs) at $z$ > 5.5 observed so far with Chandra, XMM-Newton and Swift-XRT, including the most-distant quasar ever discovered, ULAS J1120+0641 ($z$ = 7.08). This study allows us to place constraints on the mean spectral properties of the primordial population of luminous Type 1 (unobscured) quasars. Eighteen quasars are detected in the X-ray band, and we provide spectral-fitting results for their X-ray properties, while for the others we provide upper limits to their soft (0.5-2.0 keV) X-ray flux. We measured the power-law photon index and derived an upper limit to the column density for the five quasars (J1306+0356, J0100+2802, J1030+0524, J1148+5251, J1120+0641) with the best spectra (> 30 net counts in the 0.5-7.0 keV energy range) and find that they are consistent with values from the literature and lower-redshift quasars. By stacking the spectra of ten quasars detected by Chandra in the redshift range 5.7 $łe$ $z$ $łe$ 6.1 we find a mean X-ray power-law photon index of $\Gamma = 1.92_-0.27^+0.28$ and a neutral intrinsic absorption column density of $N_H 10^23$ cm$^-2$. These results suggest that the X-ray spectral properties of luminous quasars have not evolved up to $z$ $\approx$ 6. We also derived the optical-X-ray spectral slopes ($\alpha_ox$) of our sample and combined them with those of previous works, confirming that $\alpha_ox$ strongly correlates with UV monochromatic luminosity at 2500 \AA . These results strengthen the non-evolutionary scenario for the spectral properties of luminous active galactic nuclei (AGN).

@misc{nanni2017properties, abstract = {We present a systematic analysis of X-ray archival data of all the 29 quasars (QSOs) at $z$ > 5.5 observed so far with Chandra, XMM-Newton and Swift-XRT, including the most-distant quasar ever discovered, ULAS J1120+0641 ($z$ = 7.08). This study allows us to place constraints on the mean spectral properties of the primordial population of luminous Type 1 (unobscured) quasars. Eighteen quasars are detected in the X-ray band, and we provide spectral-fitting results for their X-ray properties, while for the others we provide upper limits to their soft (0.5-2.0 keV) X-ray flux. We measured the power-law photon index and derived an upper limit to the column density for the five quasars (J1306+0356, J0100+2802, J1030+0524, J1148+5251, J1120+0641) with the best spectra (> 30 net counts in the 0.5-7.0 keV energy range) and find that they are consistent with values from the literature and lower-redshift quasars. By stacking the spectra of ten quasars detected by Chandra in the redshift range 5.7 $\le$ $z$ $\le$ 6.1 we find a mean X-ray power-law photon index of $\Gamma = 1.92_{-0.27}^{+0.28}$ and a neutral intrinsic absorption column density of $N_H \le 10^{23}$ cm$^{-2}$. These results suggest that the X-ray spectral properties of luminous quasars have not evolved up to $z$ $\approx$ 6. We also derived the optical-X-ray spectral slopes ($\alpha_{ox}$) of our sample and combined them with those of previous works, confirming that $\alpha_{ox}$ strongly correlates with UV monochromatic luminosity at 2500 \AA . These results strengthen the non-evolutionary scenario for the spectral properties of luminous active galactic nuclei (AGN).}, added-at = {2017-05-01T10:12:29.000+0200}, author = {Nanni, R. and Vignali, C. and Gilli, R. and Moretti, A. and Brandt, W. N.}, biburl = {https://www.bibsonomy.org/bibtex/222fc58327ae8b5f6c9b58650b978d0de/miki}, description = {[1704.08693] The X-ray properties of z$\sim$6 luminous quasars}, interhash = {6093f7175470d631f251c7e3fba0428f}, intrahash = {22fc58327ae8b5f6c9b58650b978d0de}, keywords = {high-z quasars x-ray}, note = {cite arxiv:1704.08693Comment: 12 pages, 7 figures, accepted for publication in Astronomy and Astrophysics}, timestamp = {2017-05-01T10:12:29.000+0200}, title = {The X-ray properties of z$\sim$6 luminous quasars}, url = {http://arxiv.org/abs/1704.08693}, year = 2017 }