Probing the Cosmic X-ray and MeV Gamma-ray Background Radiation through
  the Anisotropy
  While the cosmic soft X-ray background is very likely to originate from
individual Seyfert galaxies, the origin of the cosmic hard X-ray and MeV
gamma-ray background is not fully understood. It is expected that Seyferts
including Compton thick population may explain the cosmic hard X-ray
background. At MeV energy range, Seyferts having non-thermal electrons in
coronae above accretion disks or MeV blazars may explain the background
radiation. We propose that future measurements of the angular power spectra of
anisotropy of the cosmic X-ray and MeV gamma-ray backgrounds will be key to
deciphering these backgrounds and the evolution of active galactic nuclei
(AGNs). As AGNs trace the cosmic large-scale structure, spatial clustering of
AGNs exists. We show that e-ROSITA will clearly detect the correlation signal
of unresolved Seyferts at 0.5-2 keV and 2-10 keV bands and will be able to
measure the bias parameter of AGNs at both bands. Once the future hard X-ray
all sky satellites achieve the sensitivity better than 10^{-12} erg/cm^2/s at
10-30 keV or 30-50 keV - although this is beyond the sensitivities of current
hard X-ray all sky monitors - angular power spectra will allow us to
independently investigate the fraction of Compton-thick AGNs in all Seyferts.
We also find that the expected angular power spectra of Seyferts and blazars in
the MeV range are different by about an order of magnitude, where the Poisson
term, so-called shot noise, is dominant. Current and future MeV instruments
will clearly disentangle the origin of the MeV gamma-ray background through the
angular power spectrum.
