Astrophys. J., 807, L10 (2015/July-1)
Enhancement of the 6.4 keV line in the inner galactic ridge: proton-induced fluorescence?
NOBUKAWA K.K., NOBUKAWA M., UCHIYAMA H., TSURU T.G., TORII K., TANAKA T., CHERNYSHOV D.O., FUKUI Y., DOGIEL V.A. and KOYAMA K.
Abstract (from CDS):
A common idea for the origin of the Galactic diffuse X-ray emission, particularly that of the iron lines from neutral and highly ionized atoms, is a superposition of many cataclysmic variables and coronally active binaries. In this scenario, the flux should symmetrically distribute between the east and west on the plane with respect to Sagittarius A* because the stellar mass distribution determined by infrared observations is nearly symmetric. This symmetry is confirmed for the highly ionized iron line as well as the continuum emission. However, a clear excess of the neutral iron line in the near east of the Galactic center compared to the near-west side is found. The flux distribution of the excess emission well correlates with the molecular column density. The X-ray spectrum of the excess emission is described by a power-law continuum plus a 6.4 keV line with a large equivalent width of ∼1.3 keV, which is hardly explained by the low-energy electron bombardment scenario. The longitudinal and latitudinal distribution of the excess emission disfavors the X-ray irradiation, either by Sagittarius A* or by nearby X-ray binaries. Then, the low-energy proton bombardment is the most probable origin, although the high-energy density ∼80 eV/cm3 in 0.1-1000 MeV is required and there is no conventional proton source in the vicinity.
cosmic rays - Galaxy: disk - X-rays: ISM
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