{'fraction_non_alphanumeric': 0.034106412005457026, 'fraction_numerical': 0.017394270122783082, 'mean_word_length': 4.065630397236615, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Study of X-ray Emission from the Giant Molecular Clouds in the Galactic Center Region

There are K-shell emission lines of neutral Fe (Fe I Kα) correlated with giant molecular clouds in the Galactic center (GC) region. The Fe I Kα emission is one of the key for the structure and activity of the GC, including the super-massive black hole Sagittarius A* (hereafter Sgr A*) with a huge mass 4 × 106 M ̄. The origin of the Fe I K is still open question, but possibly due either to X-ray radiation from an external object (X-ray reflection nebula: XRN) or to bombardment of low energy cosmic-ray electrons (LECRe) to neutral atoms in dense molecular clouds. In order to resolve the problem, we made deep observations of molecular clouds emitting the Fe I Kα line in the Sagittarius (Sgr) A, B1, B2, and C regions with the Japanese X-ray scientific satellite Suzaku. We discovered Kα lines of neutral Ar, Ca, Cr, Mn atoms in addition to those of Fe and Ni from a cloud in the Sgr A region. The equivalent widths of these emission lines require that the metal abundances in the GC region are ∼1.6 and ≥ 4 solar values in the XRN and LECRe scenarios, respectively. On the other hand, the X-ray spectrum of the hot plasma extended over the GC region exhibits the metal abundances of 1–2 solar values. The XRN model agrees with these results. We detected X-ray emissions with strong Fe I Kα lines from molecular clouds in the Sgr B1 and C regions. The X-ray spectra consist of the Fe I Kα lines with large equivalent widths of 1–2 keV and deeply-absorbed hard continua (column density NH ∼ 1023 cm−2, photon index Γ ∼ 1.7), and hence these clouds are also likely to be XRNe. We found that the Fe I Kα fluxes of the two clouds in the Sgr B2 region had decreased in correlation to the hard-continuum fluxes by factor of 0.4–0.5 from 2005 to 2009. The time interval of 4 years is nearly equal to the light-traveling across the clouds. The rapid and correlated time-variability in addition to the large equivalent width of Fe I Kα are consistently explained by the XRN scenario due to an X-ray flare from an external source with the duration time of shorter than 4 years. The peak-position of the Fe I-Kα emission shifted slightly to a larger distance from the GC, Sgr A*, and hence the X-ray flare source should be located in the Sgr A*-side with respect to Sgr B. Based on these facts, the luminosity of the X-ray flare is needed to be larger than 1040 erg s−1, which is 50 times larger than the Eddington limit of an object with the sun’s mass. Therefore Sgr A* is an unique candidate to illuminate the clouds in X-ray. When the Sgr A* flare is applied to the origin of the Fe I K emission from the other clouds, the required luminosities are similar values of ∼ 1041 erg s−1. Thus, we reached a conclusion that the super-massive black hole Sgr A* made a single X-ray flare 300 years ago and illuminated the molecular clouds in the vicinity.