XMM-Newton SAS Home Page
XMM-Newton Science Analysis System

omqualitymap (omqualitymap-1.5) [xmmsas_20211130_0941-20.0.0]

Mode 1- Quality-image pixel setting

The purpose of this mode is to populate the QUALITY image extension within individual OM images using the source-list data produced by omdetect.

Source-detection over each individual image is performed in detector coordinates using the task omdetect. This yields individual source-lists with catalogued detector pixel-coordinates, count-rates and source morphology data. Quality issues are related to either source-brightness, proximity to other sources, or image location. This information is collated from the source-list and recorded in a two-dimensional bit map that we will refer to as the “quality map”. Quality issues are generally recorded over a cluster of pixels in the quality image.

The following is a list of the QUALITY pixel bits set, together with a description of the size and shape of the region containing the pixels whose bits are set. All coordinates refer to detector coordinates (0-2048, 0-2048) and heights, radii, etc, to unbinned pixels.

  1. Bit 0 (Bad Pixel) Not set- please see section below
  2. Bit 1 (Read-out streak) A series of 16 unbinned vertical columns, horizontally-centred on a star of raw count-rate $\ge$ 60 counts/sec.
  3. Bit 2 (Smoke-ring) A circular region centred on the positionally-dependent, empirically-derived centre of a smoke-ring. The circle has a radius of 38 arcsecs and the flag is set for all smoke rings with parent sources $\ge$ 60 counts/sec.

  4. Bit 3 (Diffraction spikes ) Four rectangular regions rotated from the vertical by $\pm 45$ and $\pm$ 135 degrees. The half-width of a rectangle is 10 unbinned pixels and they extend radially, 50 to 250 unbinned pixels from the centre of the star. This flag is only set if the central source $\ge$ 70 counts/sec.

  5. Bit 4 (Modulo-8 fixed pattern) Rectangular region centred on a source $\ge$ 60 counts/sec. The rectangle has a minimum half-width of 16 unbinned pixels. Pattern extent is related to source brightness, source morphology and local field density. The algorithm will attempt to determine the extent of the pattern and will adjust the dimensions of the rectangle accordingly.

  6. Bit 5 (Central-enhancement region) A circular region centred upon detector coordinate (992,1063) with a radius of 160 pixels.

  7. Bit 6 (Bright-source close proximity) is set by omdetect.

  8. Bit 7 (Image edge) Any pixel within a border distance of 12 unbinned pixels.
  9. Bit 7 (OM detector corner) Any pixel outside the circle centred on x=979.2, y=1016.0 with a radius of 1300 unbinned pixels.

  10. Bit 8 (Point-source lies within extended source) is set by omdetect.

  11. Bit 9 (Weird source- bright (hot) isolated pixels) Box centred on any abnormally isolated bright pixel of half-width 12 unbinned pixels.
  12. Bit 10 (One or more different exposure pixels within source photometry-aperture). This bit is set by omdetect and only when source-photometry is performed using an exposure image .

XMM-Newton SOC -- 2021-11-30