The isotropy of the X-ray background in the energy range 2-18 keV

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Abstract
A study of the large-scale isotropy of the X-ray background in the energy range 2–18 keV has revealed significant variations in the intensity distribution over the sky |$(\,\left|b \right|\,\gt\,{20}^{^{\circ} })$| A galactic component is apparent which contributes between 2.5 and 7.2 per cent of the background between galactic latitudes 90 and 20°, respectively. We find that the most plausible interpretation of this feature is in terms of inverse Compton scattering of starlight and the microwave background by low-energy cosmic ray electrons. We investigate the residual background variations in terms of both 24- and 12-hr effects. A significant oblate 12-hr variation is found. The pole position of this effect |$(l\,\approx\,{245}^{^{\circ} },\,b\,\approx\, {53}^{^{\circ} })$| is coincident, within the errors, with the pole position of the 24-hr anisotropy reported in the microwave background by Smoot, Gorenstein & Muller. We discuss a possible interpretation of this result.

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