Ximage

Remove

The REMOVE_SOURCES command can be used to remove any area from an image. By default the removed area is replaced with random values based on the background level, although the CONSTANT qualifier can be used to set an explicit value for the removed area.

The removed area may defined as:

  • a box selected with the mouse (remove/cursor)
  • a region from a region file (remove/regionfile=[filename])
  • within x/y limits (remove/xmin=x1/xmax=x2/ymin=y1/ymax=y2)
  • detected sources (remove/detect_sources)

The removal of detected sources can be useful for seeing how well the detection process was performed. Searching for sources, removing them, then searching again, removing, and so on can be used to clean a crowded region of its sources.

Sosta

The SOSTA command calculates the source counting rates and statistics corrected for vignetting, point spread function and exposure.

The location of sources may be set through the /XPIX and /YPIX qualifiers, selected with the mouse (the default), or defined as the detected sources found by the SEARCH or DETECT command (i.e. sosta/detect_sources).

By default, SOSTA will use counts in a box that corresponds to 66% of the encircled energy function (EEF), and will use a background from a region surrounding the source, outside the 98% EEF boundary. The radii of the box-shaped background region can be modified with the /INNER_RADIUS and /OUTER_RADIUS qualifiers. The background may also be set directly with /BACKGROUND_LEVEL or calculated based on an area of the image with /BOX_BACKGROUND. Note that the results from the BACKGROUND command are not used by the SOSTA command. The background calculation is completely internal to SOSTA.

The uncertainty in the count rate returned by SOSTA is purely statistical i.e. does not include systematic errors. SOSTA will estimate the optimum box size to maximize the signal to noise ratio. This is given at the end of each run. By using the option `/OPTIMIZE` then SOSTA will go around a second time, and use the optimum box size to calculate the optimum source statistics.

Counts

The COUNTS command sums the total number of counts within an area. The summed area may defined as:
  • a box selected with the mouse (by default)
  • a region from a region file (counts/regionfile=[filename])
  • within x/y limits (counts/xmin=x1/xmax=x2/ymin=y1/ymax=y2)

The COUNTS command does not apply any correction to the total counts nor does it subtract the background. When SOSTA's results are suspect, the untouched count values can be determined with the COUNTS command. For example, if a source is not pointlike the estimated count rate from SOSTA is in general inaccurate and likely to be underestimated. The COUNTS command can provide a good estimate of the intensity of extended sources.

To sum counts for detected sources, a perl script (reggen.pl) is available, which will generate region files for the boxes listed in the output file from SEARCH/OUT=[filename]. Those region files may then be used with the COUNTS command. See the Additional Scripts page for details.


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Last modified: Wednesday, 29-Mar-2006 14:35:33 EST