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Strong iron fluorescence at 6.4 keV and hard-X-ray emissions from giantmolecular clouds in the Galactic center region have been interpreted asreflections of a past outburst of the Sgr A* supermassive black hole. Carefultreatment of multiple interactions of photons in a complicated geometry isessential to modeling the reprocessed emissions from the dense clouds. Wedevelop a new calculation framework of X-ray reflection from molecular cloudsbased on Monte Carlo simulations for accurate interpretation of high-qualityobservational data. By utilizing this simulation framework, we present thefirst calculations of morphologies and spectra of the reflected X-ray emissionfor several realistic models of Sgr B2, which is the most massive molecularcloud in our Galaxy. The morphology of scattered hard X-rays above 20 keV issignificantly different from that of iron fluorescence due to their largepenetrating power into dense regions of the cloud, probing the structure of thecloud. High-resolution spectra provide quantitative evaluation of the iron lineincluding its Compton shoulder to constrain the mass and the chemicalcomposition of the cloud as well as the luminosity of the illuminating source.These predictions can be checked in the near future with future X-ray missionssuch as NuStar (hard X-rays) and ASTRO-H (both iron lines and hard X-rays).

X-ray Diagnostics of Giant Molecular Clouds in the Galactic Center Region and Past Activity of Sgr A*