Proton Contribution to K-Shell Excitation at Diffusive Shock Acceleration Sites

Details Proton Contribution to K-Shell Excitation at Diffusive Shock Acceleration Sites Proton Contribution to K-Shell Excitation at Diffusive Shock Acceleration Sites

Mar 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008head...10.3110k&link_type=abstract

American Astronomical Society, HEAD meeting #10, #31.10

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Scientific paper

Evidence for proton acceleration has been sought in TeV gamma-ray spectra observed at particle acceleration sites in Galactic supernova remnants (SNRs) but definitive conclusion has not yet been reached. We show in this paper that a high proton flux impinging into a dense molecular cloud will accompany Fe K-shell line X-ray emission at an intensity possibly observable with high-resolution imaging X-ray spectrometers currently operational. Inner atomic levels can be ionized or excited by protons as well as by electrons. X-ray line fluorescences by electrons are always accompanied by the bremsstrahlung X-ray continuum. Accelerated protons, on the other hand, can contribute to X-ray lines but not to the continuum X-ray spectrum. Until now the contribution of protons (and nuclei) have been ignored in the line X-ray analysis. We present the K-shell line fluorescence cross-sections as functions of the incident electron and proton energies for the neutral, He-like, and H-like Fe atoms to facilitate future broadband analyses involving hard X-ray detectors, GLAST-Large Area Telescope, and TeV gamma-ray telescopes. Expected K-shell line spectra is shown for the proton and electron fluxes predicted by a non-linear diffusive shock acceleration model of a young SNR imbedded in a gaseous environment with density of 10/cm3. The proton contribution can be interpreted as an anomalously large line-to-continuum ratio or equivalently as a high metallic abundance. In this relation, we also present the line-to-continuum ratio using a precision bremsstrahlung cross-sections using the computer code PENELOPE. Existing measurements on Fe K-shell line intensity and line-to-continuum ratio (or absence thereof) set upperlimits to the proton flux at acceleration sites in high gas density environment. Atomic line fluorescence by protons will become an interesting research theme for the micro-calorimeter to be installed aboard the NeXT mission of JAXA and NASA.

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