detect - source detection

  detect[/qualifiers]

Locates point sources in the current image by means of a sliding-cell method. The average background intensity is estimated in several small square boxes uniformly located within the image (see command BACKGROUND for a more detailed description). The position and intensity of each detected source are calculated in a box whose size maximizes the signal-to-noise ratio. If the source is not pointlike the estimated count rate is in general inaccurate and likely to be under-estimated. A good estimate of the intensity of extended sources can be obtained with command SOSTA.

Corrections for telemetry and instrumental dead times, for vignetting effects and for the fraction of the source counts that fall outside the box where the net counts are estimated are applied. Count rate errors include both statistical and systematic uncertainties added quadratically. To minimize the number of spurious sources detected the threshold used by DETECT is somewhat conservative. Consequently, some sources with intensity just above the image background can be missed. In order to allow DETECT to obtain a sufficiently good estimate of the background only images of size 128x128 pixels or larger should be used. Maximum accuracy is obtained running DETECT on full resolution images.

detect/draw_rej_back_boxes

This causes detect to display all background boxes which have NOT been used for the estimation of the background Different colors correspond to different reasons for rejection.

detect/source_box_size=

This defines the size (in image pixels) of the search cell. The default value of the search cell size depends on the instrument PSF and on the image pixel size. Try increasing it to reduce confusion.

detect/back_box_size=m

Define the size, m, (in image pixels) of the boxes where the image background is estimated. Image size must be a multiple of the background box size. Allowed background box sizes are 16, 32, 64, 128, etc...

detect/bright

Do not merge the excesses before optimizing the box centroid. This is slower, but can be better for crowded fields and fields containing bright sources.

detect/plot_excesses

Plot the excesses. This is a useful diagnostic if things go wrong.

detect/prob_limit

Change the background probability limit from the default value (1E-06).

detect/snr_threshold

Change the signal to noise acceptance threshold from its default value of 2.

detect/thr_scaling

Scale the threshold for detecting source excesses. Try increasing it to 1.1 or 1.2 or 1.3 to reduce problems with fluctuations from extended emission.

detect/file_out

To specify an output filename which contains the detect results. The default value is the input filename with extension '.det'. The output file from detect is a plain ascii.

Examples:

detect              ! Search for all point sources using the default values.
 
detect/source=10    ! Search for point sources using a search cell size of
                    ! 10 image pixels
 
detect/draw_rej     ! Draw the background boxes that have been rejected to
                    ! be drawn onto the image (if this has been displayed).
                    ! All other parameters are set to default values.
 
detect/back=32      ! Estimate the image background using boxes of size 32
                    ! image pixels. All other parameters are set to default
                    ! values.