Magnetar Broadband X-Ray Spectra Correlated with Magnetic Fields: Suzaku Archive of SGRs and AXPs Combined with NuSTAR, Swift, and RXTE
- The Hakubi Center for Advanced Research, Kyoto University, Kyoto 606-8302 (Japan)
- Department of Physics, Yamagata University, Kojirakawa 1-4-12, Yamagata, 990-8560 Japan (Japan)
- Department of Physical Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526 (Japan)
- Center for Gravitational Physics, Yukawa Institute for Theoretical Physics, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502 (Japan)
- Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, AIST Central 7, Tsukuba, Ibaraki 305-8567 (Japan)
- Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 (Japan)
- Department of Physics and Mathematics, Aoyama Gakuin University, 5-10-1 Fuchinobe, Sagamihara, Kanagawa 252-5258 (Japan)
- High Energy Astrophysics Laboratory, RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan)
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 ≳10 keV with the 15–60 keV flux of ∼1–11×10{sup −11} erg s{sup −1} cm{sup −2}. The hard X-ray luminosity L{sub h}, relative to that of a soft-thermal surface radiation L{sub s}, tends to become higher toward younger and strongly magnetized objects. Their hardness ratio, updated from a previous study and defined as ξ=L{sub h}/L{sub s}, is correlated with the measured spin-down rate P-dot as ξ=0.62×( P-dot /10{sup −11}ss{sup −1}){sup 0.72}, corresponding to positive and negative correlations with the dipole field strength B{sub d} (ξ∝B{sub d}{sup 1.41}) and the characteristic age τ{sub c} (ξ∝τ{sub c}{sup −0.68}), 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 L{sub s} ∼ 10{sup 35} erg s{sup −1}, which are comparable to those of persistently bright ones, and fade back to ≲10{sup 32} erg s{sup −1}. Spectral properties are discussed in the framework of the magnetar hypothesis.
- OSTI ID:
- 22872587
- Journal Information:
- Astrophysical Journal, Supplement Series, Vol. 231, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0067-0049
- Country of Publication:
- United States
- Language:
- English
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