BROADBAND STUDY WITH SUZAKU OF THE MAGNETAR CLASS

Abstract

keV) spectra of the persistent X-ray emission from 9 magnetars were obtained with Suzaku, including 3 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 7 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 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) × (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 hardness ratio is also positively correlated with their surface magnetic fields with a correlation coefficient of 0.873. In addition, the hard-tail component becomes harder towards sources with older characteristic ages, with the photon index changing from ∼1.7 to ∼0.4.

The Sleeping Monster: NuSTAR Observations of SGR 1806–20, 11 Years After the Giant Flare

“…4, are quite similar to the hard X-ray tail components in other magnetars (e.g., see Götz et al 2006;Enoto et al 2010;Vogel et al 2014;Tendulkar et al 2015;Younes et al 2017;Enoto et al 2017). Yet, the power-law fit index of Γ = 1.33 ± 0.03 we obtain is slightly flatter than the typical values obtained in other observations of this source.…”

“…Yet, the power-law fit index of Γ = 1.33 ± 0.03 we obtain is slightly flatter than the typical values obtained in other observations of this source. Mereghetti et al (2005) (Enoto et al 2010) determined Γ = 1.7 ± 0.1 with 2007 data from Suzaku. A more recent summary of Suzaku observations for SGR 1806-20 and other magnetars is presented in (Enoto et al 2017).…”

“…1 of Enoto et al (2010). This property of an unusually high luminosity for the PL component (more so than for other magnetars; see Götz et al 2006;Enoto et al 2010) provides a significant constraint on resonant upscattering models that is yet to be fully explored. It affords the prospect of probes of the emission geometry and the values of the relativistic electron Lorentz factors and number density.…”

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

“…Our previous study of 9 SGRs and AXPs utilizing Suzaku (Enoto et al 2010a, hereafter Paper I) suggested that 1) phase-averaged Xray radiation of SGRs/AXPs commonly consists of the SXC below 10 keV and the HXC above 10 keV in both quiescent states and transient outbursts, 2) Γ h depends on B d and τ ch , and 3) their wide-band spectral properties are tightly correlated with B d and τ ch .…”

X-ray Observations of Neutron Stars

“…A prototypical AXP 4U 0142+61 shows the both components [9], and in 2009, we discovered a hard power-law component from a transient source 1E 1547.0−5408 [8]. Based on our Suzaku legacy, we pointed out that the broad-band spectral shape of magnetars changes as the magnetic field decays [6,11]. For example, a wide-band hardness ratio, defined as the 1-60 keV X-ray luminosity L h of the hard X-ray component relative to those of the soft X-ray one L s , shows a positive correlation of the dipole magnetic field B d .…”