Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aipc..599..959s&link_type=abstract
X-RAY ASTRONOMY: Stellar Endpoints,AGN, and the Diffuse X-ray Background. Edited by Nicholas E. White, Giuseppe Malaguti, and G
Astronomy and Astrophysics
Astronomy
1
X-Ray Sources, X-Ray Bursts, Interstellar Medium And Nebulae In Milky Way, Background Radiations
Scientific paper
The Galactic ridge X-ray emission (GRXE) is an enhanced X-ray emission along the Galactic plane, whose origin still remains unknown. The GRXE was studied for the first time in the energy band of 0.5 -10 keV with a spatial resolution of 3' by the ASCA Galactic plane survey which covers the spatial area of |l|<~45° and |b|<~0.4° almost uniformly. We determined the large scale distribution of the GRXE after eliminating discrete X-ray sources with a flux above10-12.5 ergs cm-2 s-1 and revealed that the volume emissivity of the GRXE is highly concentrated within the 4 kpc arm. We resolved 163 discrete X-ray sources by imaging analysis and obtained the LogN-LogS relations of those sources. In the hard (2-10 keV) band, the slope of the LogN-LogS relation is significantly smaller than 1. Considering a scale height of the Galactic plane covered by the ASCA Galactic plane survey, we conclude that the slope of the LogN-LogS relation represents that the spatial distribution of the sources has a scale height as small as ~10 pc, that the sources are distributed in arm-like structures, and/or that the relation reflects the luminosity function rather than the spatial distribution. We analyzed small-scale spatial intensity fluctuation of the GRXE after subtracting the large scale variations and the contributions of resolved discrete sources. The residual small-scale fluctuation is found to remain significantly over the photon-counting Poisson fluctuation. However, in the 2-10 keV band, the amplitude can be explained by the fluctuation of the cosmic X-ray background coming through the Galactic interstellar medium. From this, we can obtain a strong constraint to a flux and a number density of discrete sources if we are to explain the GRXE with a sum of discrete sources; more than 107 sources with the luminosity smaller than 1031 ergs s-1 must exist in the Galaxy. This source number density is larger by three orders of magnitude than that of CVs in the solar neighborhood, which would be a plausible candidate for the discrete source origin. Thus, We conclude that the diffuse emission origin should be much more probable even if it has large problems. .
Kaneda Hidehiro
Matsuzaki Katsuhiko
Mitsuda Kazu
Sugizaki Mutsumi
Yamauchi Shigeo
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