next up previous contents index
Next: Auroral Induced X-Ray Background Up: 3.6 PSPC Background Previous: Particle Background

Scattered Solar X-ray Background


[Snowden and Freyberg1993]

At the altitude of ROSAT ( tex2html_wrap_inline17069 550km), and with the zenith-angle observation constraint (observations are made at tex2html_wrap_inline17071 ), the scattering is dominated by atomic oxygen  with Thomson scattered X-rays in the 1/4keV band and oxygen K tex2html_wrap_inline17073 fluorescent scattered X-rays at 0.53keV. Field of view integrated minimum count rates of tex2html_wrap_inline17075 counts s tex2html_wrap_inline17077 ( tex2html_wrap_inline17079 countss tex2html_wrap_inline17081 arcmin tex2html_wrap_inline17083 , on axis) during day-side observations with excursions to tex2html_wrap_inline17085 40countss tex2html_wrap_inline17087 ( tex2html_wrap_inline17089 countss tex2html_wrap_inline17091 arcmin tex2html_wrap_inline17093 ) or more in particularly bad geometries in the 0.1-1.0 keV band are found. Typical cosmic background count rates in the same band range from 3-12 counts s tex2html_wrap_inline17097 ( tex2html_wrap_inline17099 to tex2html_wrap_inline17101 countss tex2html_wrap_inline17103 arcmin tex2html_wrap_inline17105 , on axis), demonstrating the possible severity of the contamination.

The temporal variation of the solar scattered X-ray background is dominated by the observation-geometry induced variations of the sunlit column density of Earth's atmosphere along the observation line of sight. This variation can be adequately modeled allowing a reasonable subtraction of the background counts.

The severity of the contamination by scattered solar X-rays has been much reduced as the mission has progressed, due to the reduced solar flux as solar maximum is left behind (ROSAT was launched close to solar maximum). The reduction comes both from the lower atmosphere (which also adds to the longevity of the mission because of reduced atmospheric drag) and from a lower solar X-ray luminosity.

If you have problems/suggestions please send mail to rosat_svc@mpe-garching.mpg.de