Exploratory X-Ray monitoring of luminous radio-quiet quasars at high redshift: extended time-series analyses and stacked imaging spectroscopy
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Thomas, Marcus O.
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Exploratory X-Ray monitoring of luminous radio-quiet quasars at high redshift: extended time-series analyses and stacked imaging spectroscopy
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Exploratory X-Ray Monitoring of Luminous Radio-quiet Quasars at High Redshift: Extended Time-series Analyses and Stacked Imaging Spectroscopy
Marcus O. Thomas1, Ohad Shemmer1, W. N. Brandt2,3,4, Maurizio Paolillo5,6,7, Shai Kaspi8, Cristian Vignali9,10, Paulina Lira11, and Donald P. Schneider2,3
Published 2021 December 15 • © 2021. The American Astronomical Society. All rights reserved.
The Astrophysical Journal, Volume 923, Number 1
Citation Marcus O. Thomas et al 2021 ApJ 923 111
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Abstract
We present three new Chandra X-ray epochs along with new ground-based optical–UV observations as the third installment in a time-series analysis of four high-redshift (z ≈ 4.1–4.4) radio-quiet quasars. In total, we present nine epochs for these sources with rest-frame temporal baselines of ∼1300–2000 days. We utilize the X-ray data to determine basic variability properties, as well as produce mean spectra and stacked images based on effective exposure times of ∼40–70 ks per source. We perform time-series analyses in the soft and hard bands, separately, and compare variability properties to those of sources at lower redshifts and luminosities. The magnitude of X-ray variability of our sources remains consistent with or lower than that of similar sources at lower redshifts, in agreement with the variability–luminosity anticorrelation. The mean power-law photon indices in the stacked Chandra spectra of our sources are consistent with the values measured from their archival XMM-Newton spectra separated by about 3 yr in the rest frame. Along with the X-ray observations, we provide near-simultaneous optical monitoring of the sources in the optical–UV regime. The overall variability in the optical-to-X-ray spectral slope is consistent with sources at lower redshifts, and the optical–UV observations display mild variability on monthly timescales.
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National Aeronautics & Space Administration (NASA) GO819072X
NAS8-03060
CXC grant GO0-21080X
V. M. Willaman Endowment
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The Astrophysical Journal, 923:111 (18pp), 2021 December 10
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