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Magnetar Broadband X-ray Spectra Correlated with Magnetic Fields: Suzaku Archive of SGRs and AXPs Combined with NuSTAR, Swift, and RXTE

Enoto, Teruaki and Shibata, Shinpei and Kitaguchi, Takao and Suwa, Yudai and Uchide, Takahiko and Nishioka, Hiroyuki and Kisaka, Shota and Nakano, Toshio and Murakami, Hiroaki and Makishima, Kazuo (2017) Magnetar Broadband X-ray Spectra Correlated with Magnetic Fields: Suzaku Archive of SGRs and AXPs Combined with NuSTAR, Swift, and RXTE. Astrophysical Journal Supplement Series, 231 (1). Art. No. 8. ISSN 1538-4365. doi:10.3847/1538-4365/aa6f0a.

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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 x 10^(-11) erg s^(−1) cm^(−2). The hard X-ray luminosity L_h, relative to that of a soft-thermal surface radiation L_s, tends to become higher toward younger and strongly magnetized objects. Their hardness ratio, updated from a previous study and defined as ξ = L_h/L_s, is correlated with the measured spin-down rate P as ξ = 0.62 x (P/10^(-11)s s^(-1))^(0.72), corresponding to positive and negative correlations with the dipole field strength B_d (ξ ∝ B^(1.41)_d) and the characteristic age τ_c (ξ ∝ τ_c^(-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_s ~ 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.

Item Type:Article
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URLURL TypeDescription Paper
Enoto, Teruaki0000-0003-1244-3100
Shibata, Shinpei0000-0002-8554-9240
Additional Information:© 2017 The American Astronomical Society. Received 2016 October 28; revised 2017 April 20; accepted 2017 April 20; published 2017 July 19. The authors would like to express their thanks to the Suzaku team for their prompt ToO observations, and to Prof. Hiroyuki Nakanishi for providing his hydrogen column density map of our Galaxy. This work was supported by JSPS KAKENHI grant numbers, 12J03320, 15H00845, 15H03653, 16H00869, 16H02198, 16K17665, 16J06773, 25105507, and 25400221, and the Hakubi project at Kyoto University. This research was also supported by the Munich Institute for Astro- and Particle Physics (MIAPP) of the DFG cluster of excellence "Origin and Structure of the Universe."
Subject Keywords:catalogs – pulsars: general – stars: magnetars – stars: magnetic field – stars: neutron – X-rays: stars
Issue or Number:1
Record Number:CaltechAUTHORS:20170425-091843035
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Official Citation:Teruaki Enoto et al 2017 ApJS 231 8
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:76904
Deposited By: Joy Painter
Deposited On:25 Apr 2017 16:30
Last Modified:15 Nov 2021 17:03

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