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We present three new Chandra X-ray epochs along with new ground-basedoptical-UV observations as the third installment in a time-series analysis offour high-redshift ($z\sim4.1-4.4$) radio-quiet quasars (RQQs). In total, wepresent nine epochs for these sources with rest-frame temporal baselines of$\sim1300-2000$ days. We utilize the X-ray data to determine basic variabilityproperties, as well as produce mean spectra and stacked images based oneffective exposure times of $\sim40-70$ ks per source. We perform time-seriesanalyses in the soft and hard bands, separately, and compare variabilityproperties to those of sources at lower redshifts and luminosities. Themagnitude of X-ray variability of our sources remains consistent with or lowerthan that of similar sources at lower redshifts, in agreement with thevariability-luminosity anti-correlation. The mean power-law photon indices inthe stacked Chandra spectra of our sources are consistent with the valuesmeasured from their archival XMM-Newton spectra separated by about three yearsin the rest frame. Along with the X-ray observations we providenear-simultaneous optical monitoring of the sources in the optical-UV regime.The overall variability in the optical-to-X-ray spectral slope is consistentwith sources at lower redshifts and the optical-UV observations display mildvariability on monthly timescales.

Exploratory X-Ray Monitoring of Luminous Radio-Quiet Quasars at High Redshift: Extended Time-Series Analyses and Stacked Imaging Spectroscopy