Spatial maps of heliospheric and geocoronal X‐ray intensities due to the charge exchange of the solar wind with neutrals

Abstract

[1] X-rays are generated throughout the heliosphere and the terrestrial magnetosheath as a consequence of charge transfer collisions between heavy solar wind ions and interstellar and geocoronal neutrals, respectively. Simple models of this X-ray emission have been presented in the past, but results from a more sophisticated model are described in this paper. In particular, to obtain the densities of interstellar neutrals our X-ray model uses to determine X-ray intensities, we use the Fahr [1971] hot model although with recently determined input parameters. The geocoronal X-ray model we use in this paper has also been improved, as described in a recent paper by Robertson and Cravens [2003]. In previous papers we demonstrated that there is significant correlation between the ''longterm enhancement'' part of the soft X-ray background measured by the Röntgen Satellite (ROSAT) and the solar wind proton flux. In the current paper we determine the steadystate X-ray intensities due to the interaction between the solar wind and both interstellar neutrals and the geocoronal neutrals as a function of look direction and time of year. X-ray intensity maps are shown for both a spherically symmetric solar wind and for a latitudedependent solar wind (i.e., fast and slow solar wind regions). In all cases, the X-ray intensity is highest when the view direction is towards the Sun, but the intensity is also relatively high for view directions intersecting the gravitational focusing cone of interstellar helium. We also show a heliospheric/geocoronal X-ray intensity map for the conditions used by Snowden et al. [1995] in producing the 1/4 keV channel soft X-ray background map in galactic coordinates. Our preliminary conclusion is that very roughly 50% of the total background soft X-ray intensity in the galactic plane and 25% at high galactic latitudes can be attributed to the charge transfer process operating within the solar system, with the remaining emission coming from outside our heliosphere.INDEX TERMS: 7554 Solar Physics, Astrophysics, and Astronomy: X rays, gamma rays, and neutrinos; 2144 Interplanetary Physics: Interstellar gas; 2164 Interplanetary Physics: Solar wind plasma; 0310 Atmospheric Composition and Structure: Airglow and aurora; 2728 Magnetospheric Physics: Magnetosheath; KEYWORDS: X rays, spatial maps, charge exchange, geocorona, heliosphere, interstellar medium Citation: Robertson, I. P., and T. E. Cravens, Spatial maps of heliospheric and geocoronal X-ray intensities due to the charge exchange of the solar wind with neutrals,

Charge Transfer Reactions

“…There may be yet another source of CXE present which can be attributed to the solar system, caused by instabilities at the heliopause (Borovikov et al 2008). Compared to the geocoronal component, the heliospheric emission is expected to exhibit slower temporal variations and a different large-scale spatial distribution Robertson and Cravens 2003;Lallement 2004b). A clear distinction between these contributions, however, and especially a determination of their absolute flux, is very difficult, because of the similarity of these components and of the diffuse X-ray emission originating outside the solar system.…”

A Possible Supernova Remnant High Above the Galactic Disk

“…Observations of the diffuse soft X-ray emission from ∼million degree Galactic gas may be contaminated by geocoronal and heliospheric solar wind charge exchange (SWCX) emission (Cravens 2000;Cravens et al 2001;Robertson & Cravens 2003a, 2003bKoutroumpa et al 2006Koutroumpa et al , 2007. Periods of enhanced SWCX emission have been associated with periods of increased solar wind proton flux (Cravens et al 2001;Snowden et al 2004;Fujimoto et al 2007).…”

Imaging Plasma Density Structures in the Soft X-Rays Generated by Solar Wind Charge Exchange with Neutrals

“…Emissions from interactions with interstellar He within the heliosphere vary on a several day time scale, while emissions from interactions with the interstellar H component contribute to a quiescent zero-level offset due to the large integrating path through the heliosphere that smooths out any variations. Robertson and Cravens (2003a) mapped soft X-ray emissions as a function of look direction and time of year, finding relatively high emissions along lines of sight passing through the He focusing cone. Figure 34 shows that emissions increase from solar maximum to solar minimum.…”