Does the background vary?

(2/28/94)

Yes, the same components are found in the HRI background as in the PSPC background, but at different rates. All except the particle background originate externally to the satellite as X-rays, so the count rates are only different by the relative effective areas of the two instruments. The particle background is relatively higher for the HRI than for the PSPC and is in general the dominant background component providing count rates comparable to the cosmic background.

    - Internal 1.5(1.0-2.0) ct/sec
    - External 3.0 (1.0-10.0) ct/sec
    - XRB 1.0(0.5-2.0) ct/sec
    - Total 5.5 (2.5-14) ct/sec
               0.78  ct/sec/cm^2
               3.8E-3 ct/sec/arcmin^(-2)
               1.1E-6 ct/sec/arcsec^(-2)

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