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Дата изменения: Fri Jan 10 22:46:38 2003
Дата индексирования: Sat Dec 22 07:48:18 2007
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XMM-Newton Science Analysis System


region (region-6.2.2) [xmmsas_20030110_1802-5.4.1]

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Comments

• The scheme for defining the background extraction region defined here is preliminary. It will doubtless need to be adapted in the light of in-flight experience of the true spectral and temporal charateristics of the instrument background.

• The true PSF of the mirrors is approximately elliptical towards the edges of the field-of-view, therefore the best extraction region may be an ellipse rather than a circle, or better still a ``banana''.

• An ``optimal'' extraction radius could also be defined as that at which the PSF surface brightness falls below the local background level. It would therefore generally be larger for brigher sources. This optimises the signal:noise better than a fixed encircled energy fraction, region may be extended to use this scheme. It would require the background map to be supplied as input too, and/or the use of the EPIC detect2 source list to define the source positions (this includes information on the local background for each source).

• For very crowded sources the best extraction region may not be circular (or ellptical), it may be a segment. This might complicate the calculation of the enclosed PSF fraction though. The PPS will not deal with confused sources in any case.

• The inter-CCD gaps in EPIC are currently ignored by region, as they are assumed to be accounted for in the exposure map. If the pointing stability of XMM is exceptional, the gaps may need to be factored into the definition of sourfce and background regions.