Correlation study of temporal and emission properties of quiescent magnetars

We measured temporal and emission properties of quiescent magnetars using archival Chandra and XMM-Newton data, produced a list of the properties for 17 magnetars, and revisited previously suggested correlations between the properties. Our studies carried out with a larger sample, better spectral characterizations, and more thorough analyses not only confirmed previously-suggested correlations but also found new ones. The observed correlations differ from those seen in other neutron-star populations but generally accord with magnetar models. Specifically, the trends of the intriguing correlations of blackbody luminosity ($L_{\rm BB}$) with the spin-inferred dipole magnetic field strength ($B_{\rm S}$) and characteristic age ($\tau_{\rm c}$) were measured to be $L_{\rm BB}\propto B_{\rm S}^{1.5}$ and $L_{\rm BB}\propto \tau_{\rm c}^{-0.6}$, supporting the twisted magnetosphere and magnetothermal evolution models for magnetars. We report the analysis results and discuss our findings in the context of magnetar models.