Variability of Cometary X-Ray Emission Induced by Solar Wind Ions

Abstract

X-ray emission spectra induced by the interaction of the slow and fast solar wind components with cometary gas are calculated for typical solar wind compositions. The emission spectra arising from the charge transfer mechanism are shown to be in good agreement with observational data. The identities and intensities of the brightest spectral lines that include forbidden transitions are obtained for the slow and fast solar winds. Differences in emission spectra of individual comets occur because of variations in the solar wind composition. Comparisons with observational data for comets Levy and Hale-Bopp indicate that they were subjected to the slow solar wind. The spectra at photon energies above 500 eV fluctuate with the solar wind composition because of the varying presence of fully stripped oxygen ions. Mechanisms of X-ray photon emission at energies above 0.9 keV are discussed.

Energy levels and transition rates for helium-like ions withZ = 10–36

“…Aggarwal et al (2005Aggarwal et al ( , 2008Aggarwal et al ( , 2009Aggarwal et al ( , 2010Aggarwal et al ( , 2011Aggarwal et al ( , 2012aAggarwal et al ( ,b,c,d, 2013a included level energies and multipole rates for transitions within 1snl (n ≤ 5, l ≤ (n − 1)) configurations of helium-like ions with Z = 3−36 (except for Ne IX) using the GRASP code ). However, we show below that because they treated correlation only in a limited way, their energies differ from the experimental values by more than 3 eV, which does not meet the accuracy requirement in the fitting of observed spectra (Kharchenko & Dalgarno 2001;Kallman & Palmeri 2007;Smith 2014;Beiersdorfer 2015).…”

Charge Abundances of the Solar Wind Ions Inferred from Cometary X-Ray Spectra

“…The ratio of intensities of the triplet to singlet transitions is predicted to be in excess of 3 for the charge transfer mechanism but to be comparable to unity or less in a hot plasma . The strongest spectral feature of the cometary X-ray emission at 560 eV detected recently with the Chandra X-ray telescope Krasnopolsky et al 2002) corresponds to the emis-3 1 2 S r 1 S sion line of O ϩ6 ions at 561 eV (Kharchenko & Dalgarno 2000, No. 1, 2003 KHARCHENKO ET AL.…”

“…The presence of features in the spectrum (Krasnopolsky & Mumma 2001;Lisse et al 2001;Cravens 2002;Krasnopolsky et al 2002) supports the suggestion of Cravens (1997) that the emission arises from excited states of multicharged ions of the solar wind populated by charge transfer in collisions with the neutral particles of the cometary atmospheres. The spectral resolution of the first observations was sufficient to distinguish between the slow and fast components of the solar wind (Schwadron & Cravens 2000;Kharchenko & Dalgarno 2001) but not to establish definitively the identity and relative abundances of the solar wind ions. With improved resolution, the features could be attributed to emission lines of multiply charged ions of oxygen, neon, carbon, silicon, and magnesium (Krasnopolsky et al 2002).…”

The Solar Wind Charge-eXchange Contribution to the Local Soft X-ray Background

“…For example, a 10 6 keV plasma might be responsible for all IS diffuse emission at 0.25 keV, while at 2-4 × 10 6 K it might significantly contribute to the 3/4 keV diffuse emission as well (Raymond, 1988;McCammon and Sanders, 1990, and references therein). CX line ratios mainly depend on heavy SW ion relative abundances and collision energy (Beiersdorfer et al, 2001;Kharchenko and Dalgarno, 2001;Wargelin et al, 2008). Detailed spectral comparison of SWCX and thermal emission needs a spectral resolution that should allow to resolve char-acteristic features as the O VII triplet at 0.57 keV and in general individual lines from the continuum.…”