OVII and OVIII line emission in the diffuse soft X-ray background: heliospheric and galactic contributions

摘要

We study the 0.57 keV (O VII triplet) and 0.65 keV (O VIII) diffuse emissiongenerated by charge transfer collisions between solar wind (SW) oxygen ions andinterstellar H and He neutral atoms in the inner Heliosphere. These lines whichdominate the 0.3-1.0 keV energy interval are also produced by hot gas in thegalactic halo (GH) and possibly the Local Interstellar Bubble (LB). Wedeveloped a time-dependent model of the SW Charge-Exchange (SWCX) X-rayemission, based on the localization of the SW Parker spiral at each instant. Weinclude input SW conditions affecting three selected fields, as well asshadowing targets observed with XMM-Newton, Chandra and Suzaku and calculateX-ray emission fot O VII and O VIII lines. We determine SWCX contamination andresidual emission to attribute to the galactic soft X-ray background. We obtainground level intensities and/or simulated lightcurves for each target andcompare to X-ray data. The local 3/4 keV emission (O VII and O VIII) detectedin front of shadowing clouds is found to be entirely explained by the CXheliospheric emission. No emission from the LB is needed at these energies.Using the model predictions we subtract the heliospheric contribution to themeasured emission and derive the halo contribution. We also correct for anerror in the preliminary analysis of the Hubble Deep Field North (HDFN).