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(1) |
where is the counts within the source region,
is the total background
counts and
,
are the area of the source and background
regions respectively.
The background is simply scaled by the respective box areas; no vignetting correction of any sort is made. The error is calculated from photon statistics as:
![]() |
(2) |
NB: This is only reliable for circular source regions, see section 3.2.9