2025ApJ...992...82H

We present a systematic analysis on the X-ray variability in 13 bright quasars at z > 4.5, combining recent Swift observations from 2021 to 2023 and archival multiepoch observations. Upper limits of the luminosity measurements were included in the analysis by using the Kaplan-Meier estimator method. It is found that the high-redshift quasars exhibit X-ray variability on both short-term (hours to days) and intermediate-term (weeks to months) timescales, with short-term variability dominating the overall variation. A linear correlation exists between the global mean (${\mu }_{{L}_{2-{\rm{10keV}}}}$) and standard deviation (${\sigma }_{{L}_{2-{\rm{10keV}}}}$) of X-ray luminosities, which is independent of the X-ray photon index and optical-to-X-ray spectral slope. The localized stochastic magnetic reconnection mechanism is strongly favored, which can naturally lead to a scale-invariant power-law energy distribution and satisfactorily explain the correlation. The σ-μ correlation parallels the well-documented rms-flux relation of low-redshift active galactic nuclei (AGNs), implying that the magnetic reconnection mechanism could drive short-timescale X-ray variability in both high- and low-redshift AGNs. The highest-redshift quasar in our sample, J142952+544717 (z = 6.18), shows a luminosity distribution extending to 10⁴⁷ erg s^–1 with a not conspicuous median luminosity. On the other hand, J143023+420436 (z = 4.7), which hosts the most relativistic jet among known high-redshift blazars, is dominated in the high-luminosity regime (10⁴⁷ erg s^–1), making it an ideal target for multiwavelength follow-up observations. J090630+693030 is found to have a rest-frame period of 182.46 days, and J143023+420436 has a period of 16.89 days; both could be explained by the global evolution of plasmoid chains, in which magnetic islands formed during reconnection may merge successively.