Spatial Power Spectral Analysis of the Suzaku X-ray Background

Power spectra of spatial fluctuations of X-ray emission may impose constraints on the origins of the emission independent of that from the energy spectra. We generated spatial power spectrum densities (PSD) of blank X-ray skies observed with Suzaku X-ray observatory utilizing the modified $Δ$-variance method. Using the total measured count rate as the diagnostic tool, we found that a model consisting of the sum of two components, one for the unresolved faint point sources and one for the uniform flat-field emission, can well represent the observed PSD in three different energy bands (0.2-0.5 keV, 0.5-2 keV, and 2-10 keV); only an upper limit is obtained for the latter component in 2-10 keV. X-ray counting rates corresponding to the best-fit PSD model functions and diffuse emission fractions were estimated, and we confirmed that the sum of the counting rates of two model components is consistent with those actually observed with the detector for all energy bands. The ratio of the flat-field counting rate to the total in 0.5-2 keV, however, is significantly larger than the diffuse emission fraction estimated from the model fits of energy spectra. We discussed that this discrepancy can be reconciled by systematic effects in the PSD and energy spectrum analyses. The present study demonstrates that the spatial power spectrum is powerful in constraining the origins of the X-ray emission.

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