Motivated by recent claims of a compelling ∼3.5 keV emission line from nearby galaxies and galaxy clusters, we investigate a novel plasma model incorporating a charge exchange component obtained from theoretical scattering calculations. Fitting this kind of component with a standard thermal model yields positive residuals around 3.5 keV, produced mostly by S xvi transitions from principal quantum numbers n ≥ 9 to the ground. Such high-n states can only be populated by the charge exchange process. In this scenario, the observed 3.5 keV line flux in clusters can be naturally explained by an interaction in an effective volume of ∼1 kpc 3 between a ∼3 keV temperature plasma and cold dense clouds moving at a few hundred keV −1 . The S xvi lines at ∼3.5 keV also provide a unique diagnostic of the charge exchange phenomenon in hot cosmic plasmas.

Charge exchange (CX) has emerged in X-ray emission modeling as a significant process that must be considered in many astrophysical environments -particularly comets. Comets host an interaction between solar wind ions and cometary neutrals to promote solar wind charge exchange (SWCX). Xray observatories provide astronomers and astrophysicists with data for many X-ray emitting comets that are impossible to accurately model without reliable charge exchange data. Here, we utilize a streamlined set of computer programs incorporating multi-channel Landau-Zener theory and a cascade model for X-ray emission to generate cross sections and X-ray line ratios for a variety of bare and non-bare ion single electron capture (SEC) collisions. Namely, we consider collisions between the solar wind constituent bare and H-like ions of C, N, O, Ne, Na, Mg, Al, and Si and the cometary neutrals H 2 O, CO, CO 2 , OH, and O. To exemplify the application of this data, we model the X-ray emission of Comet C/2000 WM1 (linear) using the CX package in SPEX (Gu et al. 2016) and find excellent agreement with observations made with the XMM-Newton RGS detector. Our analyses show that the X-ray intensity is dominated by SWCX with H while H 2 O plays a secondary role. This is the first time, to our knowledge, that CX cross sections have been implemented into a X-ray spectral fitting package to determine the H to H 2 O ratio in cometary atmospheres. The CX data sets are incorporated into the modeling packages SPEX (Gu et al. 2016) and Kronos (Mullen et al. 2016).

Recent X-ray studies have shown that supernova shock models are unable to satisfactorily explain X-ray emission in the rim of the Cygnus Loop. In an attempt to account for this "anomalously" enhanced X-ray flux, we fit the region with a model including theoretical charge exchange (CX) data along with shock and background X-ray models. The model includes the CX collisions of O 8+ , O 7+ , N 7+ , N 6+ , C 6+ , and C 5+ with H with an energy of 1 keV/u (438 km/s).The observations reveal a strong emission feature near 0.7 keV that cannot fully be accounted for by a shock model, nor the current CX data. Inclusion of CX, specifically O 7+ + H, does provide for a statistically significant improvement over a pure shock model. Subject headings: atomic processes, line: formations, ISM: supernova remnants, X-rays: general 1 http://heasarc.gsfc.nasa.gov/lheasoft/ 2 http://heasarc.gsfc.nasa.gov/docs/suzaku/analysis/abc/abc.html

Recent X-ray observations of star-forming galaxies such as M82 have shown the Lyβ/Lyα line ratio of Ne X to be in excess of predictions for thermal electron impact excitation. Here we demonstrate that the observed line ratio may be due to charge exchange and can be used to constrain the ion kinetic energy to be 500 eV/u. This is accomplished by computing spectra and line ratios via a range of theoretical methods and comparing these to experiments with He over astrophysically relevant collision energies. The charge exchange emission spectra calculations were performed for Ne 10+ + H and Ne 10+ + He using widely applied approaches including the atomic orbital close coupling, classical trajectory Monte Carlo, and multichannel Landau-Zener (MCLZ) methods. A comparison of the results from these methods indicates that for the considered energy range and neutrals (H, He) the so-called "low-energy ℓ-distribution" MCLZ method provides the most likely reliable predictions.