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We present an ensemble X-ray analysis of systematic perturbations in thecentral hot gas properties for a sample of 28 nearby strong cool-core systemsselected from the HIghest X-ray FLUx Galaxy Cluster Sample (HIFLUGCS). Weanalyze their cool-core features observed with the Chandra X-ray Observatory.All individual systems in our sample exhibit at least a pair of positive andnegative excess perturbations in the X-ray residual image after subtracting theglobal brightness profile. We extract and analyze X-ray spectra of theintracluster medium (ICM) in the detected perturbed regions. To investigatepossible origins of the gas perturbations, we characterize thermodynamicproperties of the ICM in the perturbed regions and characterize theircorrelations between positive and negative excess regions. The best-fitrelations for temperature and entropy show a clear offset from the one-to-onerelation, $T_\mathrm{neg}/T_\mathrm{pos}=1.20^{+0.04}_{-0.03}$ and$K_\mathrm{neg}/K_\mathrm{pos}=1.43\pm 0.07$, whereas the best-fit relation forpressure is found to be remarkably consistent with the one-to-one relation$P_\mathrm{neg}=P_\mathrm{pos}$, indicating that the ICM in the perturbedregions is in pressure equilibrium. These observed features in the HIFLUGCSsample are in agreement with the hypothesis that the gas perturbations in coolcores are generated by gas sloshing. We also analyze synthetic observations ofperturbed cluster cores created from binary merger simulations, finding thatthe observed temperature ratio agrees with the simulations,$T_\mathrm{neg}/T_\mathrm{pos}\sim 1.3$. We conclude that gas sloshing inducedby infalling substructures plays a major role in producing the characteristicgas perturbations in cool cores. The ubiquitous presence of gas perturbationsin cool cores may suggest a significant contribution of gas sloshing tosuppressing runaway cooling of the ICM.

Systematic Perturbations of the Thermodynamic Properties in Cool Cores of HIFLUGCS Galaxy Clusters