Can Charge Exchange Explain Anomalous Soft X-Ray Emission in the Cygnus Loop?

Cumbee, Renata; Henley, David; Stancil, P. C.; Shelton, R. L.; Nolte, Jeff; Wu, Yong; Schultz, David

doi:10.1088/2041-8205/787/2/l31

Cited by 31 publications

(33 citation statements)

References 21 publications

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“…However, the lack of spatial correlation between the OVII Kα shifts and 0.7 keV enhancement (which traces the abundance inhomogeneities) suggests that CX is not the only phenomenon missing in the modelling. This is the same conclusion reached by Cumbee et al (2014) where the authors attempted to do some modelling of CX emission in the remnant.…”

Section: Comparison With Previous Worksupporting

confidence: 79%

X-ray emission from charge exchange in the Cygnus Loop SNR

Roberts

Wang

2015

Monthly Notices of the Royal Astronomical Society

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The Cygnus Loop has been the focus of substantial debate concerning the contribution of charge exchange (CX) to supernova remnant (SNR) X-ray emission. We take advantage of a distinct feature of CX, enhanced Kα forbidden line emission, and employ the energy centroid of the OVII Kα triplet as a diagnostic. Based on X-ray spectra extracted from an extensive set of Suzaku observations, we measure the energy centroid shifts of the triplet on and off the shock rim of the remnant. We find that enhanced forbidden to resonance line emission exists throughout much of the rim and this enhancement azimuthally correlates with non-radiative Hα filaments, a tracer of strong neutral-plasma interaction in the optical. We also show that alternative mechanisms cannot explain the enhancement observed. These results demonstrate the need to model the CX contribution to the X-ray emission of SNRs, particularly for shocks propagating in a partially neutral medium. Such modelling may be critically important to the correct measurements of the ionization, thermal, and chemical properties of SNRs.

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Section: Comparison With Previous Worksupporting

confidence: 79%

X-ray emission from charge exchange in the Cygnus Loop SNR

Roberts

Wang

2015

Monthly Notices of the Royal Astronomical Society

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“…Although two computational models for charge exchange have recently become available (Cumbee et al 2014;Smith et al 2014), the precise characterization of the local environment is beyond the scope of this work and therefore we used a simplified model. In the past, a single Note.…”

Section: Discussionmentioning

confidence: 99%

Studying the Interstellar Medium and the Inner Region of NPS/Loop 1 With Shadow Observations Toward Mbm36

Ursino

Galeazzi

Liu

2015

ApJ

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We analyzed data from a shadow observation of the high density molecular cloud MBM36 (l∼4°, b∼35°) with Suzaku. MBM36 is located in a region that emits relatively weakly in the 3/4 keV band compared to the surrounding North Polar Spur (NPS)/Loop 1 structure and the Galactic Bulge (GB). The contrast between high and low density targets in the MBM36 area allows one to separate the local and distant contributors to the soft diffuse X-ray background, providing a much better characterization of the individual components compared to single pointing observations. We identify two non-local thermal components, one at kT≈0.12 keV and one at kT≈0.29 keV. The colder component matches well with models of emission from the higher latitude region of the GB. The emission of the warmer component is in agreement with models predicting that the NPS is due to a hypershell from the center of the Milky Way. Geometrical and pressure calculations rule out a nearby bubble as responsible for the emission associated with the NPS. Any Galactic Halo/circumgalactic halo emission, if present, is outshined by the other components. We also report an excess emission around 0.9 keV, likely due to an overabundance of Ne IX.

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“…Charge exchange is important in setting the ionization balance in laboratory and astrophysical plasmas, as a spectral diagnostic for fusion plasmas, in determining the storage time in ion traps and storage rings, and in antihydrogen production [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Astrophysically, charge exchange occurs in planetary atmospheres and the comae of comets interacting with the solar wind, and has been hypothesized to occur at the rim of supernova remnants [16,17]. Charge exchange also occurs between solar wind ions and neutrals in the exosphere and in the heliosphere, which adds variable foreground emission for every astrophysical observation from our solar system [18][19][20][21][22][23][24][25][26].…”

Section: Introductionmentioning

confidence: 99%

Observation of highly disparateK-shell x-ray spectra produced by charge exchange with bare mid-Zions

et al. 2014

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We performed charge exchange experiments with the electron beam ion trap at the Lawrence Livermore National Laboratory and an x-ray calorimeter spectrometer. We compare the relative strength of the high-n Lyman series emission for different combinations of ions and neutral gases. Theoretical predictions show good agreement with experimental data on relative capture cross section as a function of principle quantum number n; however, the few published predictions of the distribution of captures as a function of orbital angular momentum l do not agree with experiments. Our experimental results show that the relative strength of high-n Lyman series emission varies more widely than previous experiments have found and models predict. We find that hardness ratios from charge exchange with helium and molecular hydrogen are more disparate than charge exchange with many-electron neutral species, which is likely due to differences in the relative importance of multi-electron capture. We also find that there is no clear scaling of the hardness ratio with ionization potential of the neutral species, the number of valence electrons in the neutral, or the atomic number of the ion.

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Can Charge Exchange Explain Anomalous Soft X-Ray Emission in the Cygnus Loop?

Cited by 31 publications

References 21 publications

X-ray emission from charge exchange in the Cygnus Loop SNR

X-ray emission from charge exchange in the Cygnus Loop SNR

Studying the Interstellar Medium and the Inner Region of NPS/Loop 1 With Shadow Observations Toward Mbm36

Observation of highly disparateK-shell x-ray spectra produced by charge exchange with bare mid-Zions

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