XMM-Newton Science Analysis System


ewavelet (ewavelet-3.12) [22.0.0-9173c7d25-20250127]

Algorithm

The wavelet detection involves the following steps:

• Read the input image and the exposure map.
• Generate the countrate image from the input image and exposure map.
• Generate the initial background map by scaling the exposure map in such a way that the background map contains as many “counts” as the input image.
• Do the following for several wavelet scales:

  1	generate a background map for this particular scale
  2	convolve image with the MH wavelet function
  3	find local maxima in the convolved image
  4	Check if the local maximum is significant
  5	If the maximum is significant, add the point to the source list and calculate the number of counts from the wavelet correlation value ($C_{i,j}$)

• Determine if some sources were detected at several wavelets scales. If so, choose the wavelet scale with the highest local correlation value.
• Use the detections of the same source at several wavelet scale to get some information on the source properties.
• Make a new iteration or generate the final source list.

Figure 4: Block diagram of the wavelet source detection algorithm.