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Дата изменения: Fri Mar 19 00:12:37 2004
Дата индексирования: Sat Dec 22 08:18:38 2007
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Поисковые слова: ccd

XMM-Newton Science Analysis System


arfgen (arfgen-1.65.11) [xmmsas_20040318_1831-6.0.0]

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CCD gap and bad pixel corrections

By default the task will reduce the effective area produced in the ARF if the source area contains bad pixels/columns or contains area which lies outside the CCD boundaries. For an extended source this reduction is simply the ratio of the dead area within the source region to the good area. For point sources a fine grid is used to determine the contribution to the enclosed energy of each dead point, i.e. the dead regions are normalised by the fraction of the point spread function lying within that region before being subtracted from the total effective area. The task uses the parameter extendedsource to choose between these options. Although the correction for point sources is quite good the extended source correction assumes a uniform surface brightness of the source. If this condition is not met then quite large errors can be introduced. There is currently no way of performing an accurate correction for chip gaps and bad pixels within extended source regions within arfgen.

In a similar way the task corrects for area of the source region which is outside the FOV, outside the observing window or on a CCD explicitly excluded by a CCD selection within the data subspace.

This behaviour can be turned off by setting withbadpixcorr=false. CCD gaps are automatically corrected for if withbadpixcorr=true and the pixels next to the gaps are also corrected for if the FLAG selection in the datasubspace has been set to 0. To correct for bad pixels, a file containing bad pixel extensions must be specified on the command line by badpixlocation=file. The bad pixel information is usually stored in the event file from which the spectrum was constructed. Bad columns and bad rows (MOS only) are also handled if they are specified in the OFFSETS column of the badpixlocation file.

The task creates temporary files called BADPIXnn.ds, where nn is the CCD number, in the current directory while calculating the bad pixel correction. To make these files permanent specify withfilteredset $=$ yes on the command line.