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Source flags

01n It is not a valid X-ray source
 011 false source by a hot pixel or by a bad bias value
 012 false source by a bad column
 013 false source along the readout direction of a very strong source
 014 false source by the FEP 0/3 problem
 015 double sources detected by the PSF effect 

02n It is not certain whether it is a valid X-ray source
 021 V&Ver found it might be a spurious source.

03n source properties may be subject to a large uncertainty
 031 bad pixel/column exists within source extraction radius
*032 nearby source exists within the source extraction circle
*033 nearby source exists within the bkgd extraction annulus
*034 source is found near an extended source
*035 bkgd reg overlaps with a src reg of a nearby extended src
*036 source region fall near the edge of the chip
 037 pileup
 038 uncertain source position by flag=015

04n source properties may be subject to a large uncertainty
*042 nearby source exists within the source extraction circle
*043 nearby source exists within the bkgd extraction annulus
*044 source is found near an extended source
*045 bkgd reg overlaps with a src reg of a nearby extended src
*046 source region fall near the edge of the chip

05n other cases
*051 source is extended 
 052 same source in multiple observations
 053 target of observation
 054 X-ray jet 
 055 variable

(* flagged by the XPIPE)
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To see a bad column, display the image in chip coordinates in ds9. For example, to see the bad column in the
image used as an example for flag 012, use the following command

/proj/champx3/bin/ds9 "/proj/champx2/XPIPE/OBS00945/XPIPE/evt2_ccdid0.fits.gz[bin=chipx,chipy]" &
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limit_exposure=0.80  (mean_ea/max_ea for source at the edge
limit_extended=1.5   (sigma/psf for extended source)
limit_nearby_ext=2.0 (sigma*2+src/bk radius)
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What the "value" column means for a flag:
 for 032, 033 : the number of nearby sources contaminating the source/background extraction radius.
 for 034 : ratio of the distance between the sources to the sum of the source radius and twice the gaussian sigma 
           of the extended source, i.e. [distance / (2*sigma + src. radius)].
 for 035 : same as for 034 except the bacground extraction radius is used instead of the source radius in the 
           denominator, i.e. [distance / (2*sigma + 5*src.radius)].
 for 036 : ratio of effective area within source extraction radius to maximum effective area for the observation.
           XPIPE assigns a source flag 036 when the ratio is below limit_exposure (given above).
 for 051 : ratio of the gaussian sigma of the radial profile of the extended source to the PSF (39% EE).