Suzaku Observations of the North Polar Spur: Evidence for Nitrogen Enhancement

Miller, Eric D.; Tsunemi, H.; Bautz, M. W.; McCammon, D.; Fujimoto, Ryuichi; Hughes, John P.; Katsuda, Satoru; Kokubun, M.; Mitsuda, Kazuhisa; Porter, F. S.; Takei, Yoh; Tsuboi, Y.; Yamasaki, Noriko Y.

doi:10.1093/pasj/60.sp1.s95

Cited by 42 publications

(34 citation statements)

References 67 publications

(96 reference statements)

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“…The pointing center of the Suzaku observation was (l, b) = (26.84°, 21.96°), whereas those for three XMM-Newton observations were (l, b) = (25.0°, 20.0°), (20.0°, 30.0°), and (20.0°, 40.0°), respectively, as shown in Figure 5 (left). In all observations, the observed X-ray spectra were well represented by the three-component plasma model: APEC1 + Wabs  (APEC2 + PL), where Wabs represents the Galactic absorption as a function of neutral hydrogen column density (NH), APEC1 is an unabsorbed thermal component that represents the Local Bubble (LB) emission, the contamination from the solar-wind charge exchange (SWCX; [55]), or both; APEC2 is an absorbed thermal component that represents the NPS, and an absorbed power-law component (PL) that corresponds [39] and three short (~15 ks) XMM-Newton observations [40] of the NPS. (right) Sample X-ray spectrum obtained with Suzaku [39].…”

Section: X-ray Spectramentioning

confidence: 99%

X-Ray and Gamma-Ray Observations of the Fermi Bubbles and NPS/Loop I Structures

et al. 2018

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The Fermi bubbles were possibly created by large injections of energy into the Galactic Center (GC), either by an active galactic nucleus (AGN) or by nuclear starburst more than ~10 Myr ago. However, the origin of the diffuse gamma-ray emission associated with Loop I, a radio continuum loop spanning across 100° on the sky, is still being debated. The northern-most part of Loop I, known as the North Polar Spur (NPS), is the brightest arm and is even clearly visible in the ROSAT X-ray sky map. In this paper, we present a comprehensive review on the X-ray observations of the Fermi bubbles and their possible association with the NPS and Loop I structures. Using uniform analysis of archival Suzaku and Swift data, we show that X-ray plasma with kT~0.3 keV and low metal abundance (Z~0.2 Z◉) is ubiquitous in both the bubbles and Loop I and is naturally interpreted as weakly shock-heated Galactic halo gas. However, the observed asymmetry of the X-ray-emitting gas above and below the GC has still not been resolved; it cannot be fully explained by the inclination of the axis of the Fermi bubbles to the Galactic disk normal. We argue that the NPS and Loop I may be asymmetric remnants of a large explosion that occurred before the event that created the Fermi bubbles, and that the soft gamma-ray emission from Loop I may be due to either π0 decay of accelerated protons or electron bremsstrahlung.

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Section: X-ray Spectramentioning

confidence: 99%

X-Ray and Gamma-Ray Observations of the Fermi Bubbles and NPS/Loop I Structures

et al. 2018

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“…Smith et al 2005), or Suzaku (e.g. Miller et al 2008;Yoshino et al 2009). The controversial discussion of a claimed detection of emission from warm-hot gas in the intergalactic medium (Vikhlinin et al 2001;Arnaud et al 2001;Kaastra et al 2003;Finoguenov et al 2003;Bowyer and Vikhlinin 2004;Bregman and Lloyd-Davies 2006;Nevalainen et al 2007) illustrates the far-reaching consequences of geocoronal and heliospheric X-rays.…”

Section: Geocorona and Heliospherementioning

confidence: 99%

“…The NPS is the brightest filament of the Loop I superbubble, which is known to be the largest coherent structure on the X-ray sky, probably produced by a series of supernovae and stellar winds from the nearby Sco-Cen OB association. Lallement (2009) noticed that the highest quality X-ray spectra of the NPS, obtained with XMM-Newton (Willingale et al 2003) and Suzaku (Miller et al 2008), both exhibit a peculiar feature: the emission from the (unresolved) multiplets of the He-like ions O VII and Ne IX is systematically shifted (by ∼ 10-15 eV) to lower energies relative to the H-like ions O VIII and Ne X. Exactly this behaviour is expected for charge exchange, because this process tends to brighten the flux of the spin forbidden magnetic dipole transition (at 561 eV for O VII) with respect to that of the resonance transition (at 574 eV for O VII), thus causing a systematic shift to lower energies (e.g.…”

Section: Interstellar Mediummentioning

confidence: 99%

Charge Transfer Reactions

Dennerl

2010

Space Sci Rev

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Charge transfer, or charge exchange, describes a process in which an ion takes one or more electrons from another atom. Investigations of this fundamental process have accompanied atomic physics from its very beginning, and have been extended to astrophysical scenarios already many decades ago. Yet one important aspect of this process, i.e. its high efficiency in generating X-rays, was only revealed in 1996, when comets were discovered as a new class of X-ray sources. This finding has opened up an entirely new field of X-ray studies, with great impact due to the richness of the underlying atomic physics, as the X-rays are not generated by hot electrons, but by ions picking up electrons from cold gas. While comets still represent the best astrophysical laboratory for investigating the physics of charge transfer, various studies have already spotted a variety of other astrophysical locations, within and beyond our solar system, where X-rays may be generated by this process. They range from planetary atmospheres, the heliosphere, the interstellar medium and stars to galaxies and clusters of galaxies, where charge transfer may even be observationally linked to dark matter. This review attempts to put the various aspects of the study of charge transfer reactions into a broader historical context, with special emphasis on X-ray astrophysics, where the discovery of cometary X-ray emission may have stimulated a novel look at our universe.

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“…The emission discontinuities A, B, C correspond to lines-of-sight that are tangential to the dense gas, here shown in the meridian plane containing the galactic center . (Right) XMM and Suzaku spectra of very bright NPS regions (Willingale et al 2003;Miller et al 2008). The O VIII and Ne IX emission lines seem in both cases to be shifted to lower energies, while O VIII or Ne X are not.…”

Section: Non-solar Charge Transfer X-ray Emission? the North Polar Spur?mentioning

confidence: 99%

“…In the case of the Loop 1, it is interesting to compare the highest quality NPS spectra recorded by XMM (Willingale et al 2003) and recently Suzaku (Miller et al 2008) with the model spectra. Figure 5 shows fractions of the recorded spectra at low energy.…”

Section: Non-solar Charge Transfer X-ray Emission? the North Polar Spur?mentioning

confidence: 99%