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Paper: Is the SGR B2 Cloud an X-ray Reflection Nebula?
Volume: 186, The Central Parsecs of the Galaxy
Page: 586
Authors: Murakami, H.; Koyama, K.; Sakano, M.; Tsujimoto, M.; Maeda, Y.
Abstract: We present the ASCA results of imaging spectroscopy of the giant molecular cloud Sgr B2. We found very peculiar features in this cloud; a strong 6.4-keV line emission, a low energy cutoff below 4 keV and a pronounced edge-structure at 7.1 keV. The X-ray image is extended and its peak position is shifted from the core of the molecular cloud toward the Galactic Center by about 1--2'. The X-ray spectrum and the morphology are well reproduced by a scenario where X-rays from an external source located in the Galactic Center direction are scattered by the molecular cloud Sgr B2, and come into our line of sight. Thus Sgr B2 is a new type of X-ray object, which may be called an ``X-ray reflection nebula''. The luminosity of the irradiating source is required to be >=1038 erg s-1, but no source has enough brightness. One possibility is that within the recent past, perhaps a few hundred years ago, Sgr A* was very luminous, and we are observing the ``reflected'' X-rays at present.
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