Probing Galactic Center MeV-GeV Cosmic-ray Population with Sgr B2 Fe K Emission

It has been a longstanding challenge to probe cosmicray particles at thecenter of our Galaxy. Low energy cosmicray protons (LECRp) with energies of MeVto GeV can produce 6.4 keV Fe Kalpha line and continuum Xray emission throughinteraction with cold molecular materials. The Fe Kalpha emission from thedensest Galactic Center molecular cloud Sgr B2 has been decaying for the pastdecade, which has been dominated by reflection of a past Sgr A* Xray outburst.However, as the Xray reflection component keeps fading, a constant Fe Kalphaemission component will take the stage beginning early 2017. The flux level ofthe Sgr B2 Fe K alpha emission measured in 20172018 will for the first timeput strong constraints on the MeV GeV cosmicray proton population, not previously achievable. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]