The 1–70 keV persistent spectra of 15 magnetars, observed with Suzaku from 2006 to 2013, were studied as a complete sample. Combined with early NuSTAR observations of four hard X-ray emitters, nine objects showed a hard power-law emission dominating at keV with the 15–60 keV flux of ∼1– erg s −1 cm −2 . The hard X-ray luminosity , relative to that of a soft-thermal surface radiation , tends to become higher toward younger and strongly magnetized objects. Their hardness ratio, updated from a previous study and defined as , is correlated with the measured spin-down rate as , corresponding to positive and negative correlations with the dipole field strength ( ) and the characteristic age ( ), respectively. Among our sample, five transients were observed during X-ray outbursts, and the results are compared with their long-term 1–10 keV flux decays monitored with Swift /XRT and RXTE /PCA. Fading curves of three bright outbursts are approximated by an empirical formula used in the seismology, showing a ∼10–40 day plateau phase. Transients show the maximum luminosities of ∼ 10 35 erg s −1 , which are comparable to those of persistently bright ones, and fade back to ≲10 32 erg s −1 . Spectral properties are discussed in the framework of the magnetar hypothesis.
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Enoto, T., Shibata, S., Kitaguchi, T., Suwa, Y., Uchide, T., Nishioka, H., … Makishima, K. (2017). Magnetar Broadband X-Ray Spectra Correlated with Magnetic Fields: Suzaku Archive of SGRs and AXPs Combined with NuSTAR, Swift, and RXTE. The Astrophysical Journal Supplement Series, 231(1), 8. https://doi.org/10.3847/1538-4365/aa6f0a