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Particle Background


[Snowden et al.1992], [Plucinsky et al.1993, Plucinsky et al.1996]

The PSPC rejection efficiency for particle events is very high, and leaves a residual count rate of only tex2html_wrap_inline17037 countss tex2html_wrap_inline17039 , tex2html_wrap_inline17041 countss tex2html_wrap_inline17043 cm tex2html_wrap_inline17045 keV tex2html_wrap_inline17047 or tex2html_wrap_inline17049 countss tex2html_wrap_inline17051 arcmin tex2html_wrap_inline17053 keV tex2html_wrap_inline17055 . About 77% of events originate in the detector while the remainder enter through the counter window. During typical conditions, the count rate of residual events is well correlated with the master veto rate. The master veto is the anticoincidence counter for the selection of accepted events.

The PSPC rejection efficiency for particle background events in the pulse height channel range 18-249 is well described by a power-law, a flat component, and an Al K tex2html_wrap_inline17057 line at 1.5 keV.   Typically, the ratio between the power-law and the flat components remains constant to tex2html_wrap_inline17061 , while the relative Al K tex2html_wrap_inline17063 contribution increases with increasing master veto rate. The spatial distribution of counts with pulse heights >18 is uniform over the field of view except for a small radial gradient for the internally-produced component and shadowing of the externally-produced components (Al K tex2html_wrap_inline17067 line and flat continuum) by the window support structure. During observations in low gain mode the particle background can also be monitored by the count rate in channels 260-370, since essentially all of these events are produced by particles.

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