Charge-transfer induced EUV and soft X-ray emissions in the heliosphere

Abstract

Aims. We study the EUV/soft X-ray emission generated by charge transfer between solar wind heavy ions and interstellar neutral atoms and variations of the X-ray intensities and spectra with the line of sight direction, the observer location, the solar cycle phase and the solar wind anisotropies, and a temporary enhancement of the solar wind similar to the event observed by Snowden et al. (2004) during the XMM-Hubble Deep Field North exposure. Methods. Using recent observations of the neutral atoms combined with updated cross-sections and cascading photon spectra we have computed self-consistent distributions of interstellar hydrogen, helium and highly charged solar wind ions for a stationary solar wind and we have constructed monochromatic emission maps and spectra. We have evaluated separately the contribution of the heliosheath and heliotail, and included X-ray emission of the excited solar wind ions produced in sequential collisions to the signal. Results. In most practicable observations, the low and medium latitude X-ray emission is significantly higher at minimum activity than at maximum, especially around December. This occurs due to a strong depletion of neutrals during the high activity phase, which is not compensated by an increase of the solar wind flux. For high latitudes the emission depends on the ion species in a complex way. Intensity maps are in general significantly different for observations separated by six-month intervals. Secondary ions are found to make a negligible contribution to the X-ray line of sight intensities, because their density becomes significant only at large distances. The contribution of the heliosheath-heliotail is always smaller than 5%. We can reproduce both the intensity range and the temporal variation of the XMM-HDFN emission lines in the 0.52-0.75 keV interval, using a simple enhanced solar wind spiral stream. This suggests a dominant heliospheric origin for these lines, before, during and also after the event.

Wide field‐of‐view soft X‐ray imaging for solar wind‐magnetosphere interactions

“…Kuntz et al [2015] employed more sophisticated models for heliospheric plasma [Odstrcil, 2003] and neutral [Koutroumpa et al, 2006] densities to reach similar conclusions. For the purpose of magnetospheric imaging, the disparate time scales of the variations allow for the heliospheric contribution to be subtracted off.…”

A search for a keV signature of radiatively decaying dark matter with Suzaku XIS observations of the X-ray diffuse background

“…(1) Heliospheric Solar Wind Charge Exchange (H-SWCX) and Local Hot Bubble (LHB) (2) Milky Way hot plasma Halo (MWH) (3) Cosmic X-ray Background (CXB) (4) Unresolved High Temperature Plasma (UHTP) (1): the H-SWCX is due to interaction between the Solar wind and neutral atoms in interplanetary space (Cox 1998;Cravens 2000;Koutroumpa et al 2006;Yoshitake et al 2013). The LHB is considered to be the high temperature plasma with the temperature of kT ∼ 0.1 keV (T ∼ 10 6 K) and the density of n H ∼ 0.005 cm −3 embedded in a ∼ 100 pc cavity of the cold interstellar medium in which the Solar System resides (Cox & Anderson 1982;McCammon & Sanders 1990).…”

XMM-NEWTONMEASUREMENT OF THE GALACTIC HALO X-RAY EMISSION USING A COMPACT SHADOWING CLOUD

“…a typical speed for the slow solar wind is 400 km s −1 ; e.g., Smith et al 2003). Note that the C14 CX data are for ions interacting with H. However, as He is an order of magnitude less abundant than H, and CX cross-sections involving He are typically smaller than those involving H (e.g., Koutroumpa et al 2006, Table 1), neglecting interactions between solar wind ions and He should not adversely affect our results. Note also that, because of the relatively poor spectral resolution of the XMM-Newton detectors at low energies, we did not include lines from N vi or N vii in the C14-SWCX model (these ions' Kα lines lie between those of C vi and O vii).…”