2010ApJ...722L.162E

Broadband (0.8-70 keV) spectra of the persistent X-ray emission from nine magnetars were obtained with Suzaku, including three objects in apparent outburst. The soft X-ray component was detected from all of them, with a typical blackbody temperature of kT ∼ 0.5 keV, while the hard-tail component, dominating above ∼10 keV, was detected at ∼1 mCrab intensity from seven of them. Therefore, the spectrum composed of a soft emission and a hard-tail component may be considered to be a common property of magnetars, both in their active and quiescent states. Wide-band spectral analyses revealed that the hard-tail component has a 1-60 keV flux, F_h, comparable to or even higher than that carried by the 1-60 keV soft component, F_s. The hardness ratio (HR) of these objects, defined as ξ ≡ F_h/F_s, was found to be tightly anti-correlated with their characteristic age τ_c as ξ = (3.3±0.3)x(τ_c/1 kyr)^{–0.67±0.04} with a correlation coefficient of -0.989, over the range from ξ ∼ 10 to ξ ∼ 0.1. Magnetars in outburst states were found to lie on the same correlation as relatively quiescent ones. This HR is also positively correlated with their surface magnetic fields with a correlation coefficient of 0.873. In addition, the hard-tail component becomes harder toward sources with older characteristic ages, with the photon index changing from ∼1.7 to ∼0.4.