TY - JOUR
T1 - Chandra detection of three x-ray bright quasars at z > 5
AU - Li, Jiang Tao
AU - Wang, Feige
AU - Yang, Jinyi
AU - Zhang, Yuchen
AU - Fu, Yuming
AU - Bian, Fuyan
AU - Bregman, Joel N.
AU - Fan, Xiaohui
AU - Li, Qiong
AU - Wu, Xue Bing
AU - Yu, Xiaodi
N1 - Funding Information:
The authors would like to acknowledge the anonymous referee for helpful comments and suggestions. We acknowledge Dr. Abderahmen Zoghbi at the University of Michigan for helpful discussions on the timing analysis of J074749+115352. The authors also acknowledge the use of data obtained at the Palomar 5.1 m telescope. J.T.L. acknowledge the financial support of this project from NASA and the Smithsonian Institution through grant GO0-21097X, as well as general financial support from NASA through grant 80NSSC19K0579 and from the Smithsonian Institution through grants GO9-20074X and AR9-20006X. F.W. is thankful for the support provided by NASA through the NASA Hubble Fellowship grant #HST-HF2-51448.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.
PY - 2021/1/10
Y1 - 2021/1/10
N2 - We report Chandra detection of three UV-bright radio-quiet quasars at z ≳5. We have collected a sufficient number of photons to extract an X-ray spectrum of each quasar to measure their basic X-ray properties, such as the X-ray flux, power-law photon index (Γ), and optical-to-X-ray spectral slope (αOX). J074749+115352 at z = 5.26 is the X-ray brightest radio-quiet quasar at z > 5. It may have a short timescale variation (on a timescale of ∼3800 s in the observer's frame, or ∼600 s in the rest frame), which is, however, largely embedded in the statistical noise. We extract phase folded spectra of this quasar. There are two distinguishable states: A "high soft"state with an average X-ray flux ∼2.7 times the "low hard"state, and a significantly steeper X-ray spectral slope (Γ = - 2.40+0.32 0.33 versus - 1.78+0.24 0.25). We also compare the three quasars detected in this paper to other quasar samples. We find that J074749+115352, with an SMBH mass of MSMBH ≈ 1.8 × 109Me and an Eddington ratio of λEdd ≈ 2.3, is extraordinarily X-ray bright. It has an average αOX = -1.46 ± 0.02 and a 2-10 keV bolometric correction factor of Lbol/L2-10 keV = 42.4 ± 5.8, both significantly depart from some well defined scaling relations. We compare Γ of the three quasars to other samples at different redshifts, and do not find any significant redshift evolution based on the limited sample of z > 5 quasars with reliable measurements of the X-ray spectral properties.
AB - We report Chandra detection of three UV-bright radio-quiet quasars at z ≳5. We have collected a sufficient number of photons to extract an X-ray spectrum of each quasar to measure their basic X-ray properties, such as the X-ray flux, power-law photon index (Γ), and optical-to-X-ray spectral slope (αOX). J074749+115352 at z = 5.26 is the X-ray brightest radio-quiet quasar at z > 5. It may have a short timescale variation (on a timescale of ∼3800 s in the observer's frame, or ∼600 s in the rest frame), which is, however, largely embedded in the statistical noise. We extract phase folded spectra of this quasar. There are two distinguishable states: A "high soft"state with an average X-ray flux ∼2.7 times the "low hard"state, and a significantly steeper X-ray spectral slope (Γ = - 2.40+0.32 0.33 versus - 1.78+0.24 0.25). We also compare the three quasars detected in this paper to other quasar samples. We find that J074749+115352, with an SMBH mass of MSMBH ≈ 1.8 × 109Me and an Eddington ratio of λEdd ≈ 2.3, is extraordinarily X-ray bright. It has an average αOX = -1.46 ± 0.02 and a 2-10 keV bolometric correction factor of Lbol/L2-10 keV = 42.4 ± 5.8, both significantly depart from some well defined scaling relations. We compare Γ of the three quasars to other samples at different redshifts, and do not find any significant redshift evolution based on the limited sample of z > 5 quasars with reliable measurements of the X-ray spectral properties.
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U2 - 10.3847/1538-4357/abc750
DO - 10.3847/1538-4357/abc750
M3 - Article
AN - SCOPUS:85100192173
VL - 906
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 2
M1 - abc750
ER -