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eSASS task: ERMASK

eROSITA/ermask-1.7.1


Scope

This document provides a description of the algorithm and instructions for the correct usage of the ERMASK task, which is part of eSASS (the eROSITA Science Analysis Software System).

Summary:

Create detection masks for eSASS detection chain tasks defining valid image areas which are suitable for detection. The masks are based on exposure maps created by the task EXPMAP.

Algorithms:

The task ERMASK evaluates an exposure map and calculates a detection mask according to conditions specfied by parameters threshold1 and threshold2 . The detection mask is written into the primary extension FITS extension of the output image ( int8 ) , valid pixels are set =1, pixels to excluded from source detection are set =0.

Parameter threshold1 defines an exposure threshold, given as fraction of the maximum exposure value:

  detmask(x,y) = 0
  if (expimage(x,y) > maxval(expimage)*threshold1) detmask(x,y) = 1
With parameter threshold2 additionally a maximum local exposure gradient can be set:
  if (sqrt((expimage(x+1,y)-expimage(x-1,y))**2 + (expimage(x,y+1)-expimage(x,y-1))**2) > expimage(x,y)*threshold2 ) detmask(x,y) = 0
The detection pipeline requires only detection mask, if images from the same instrument in several energy bands are processed.

Parameters:

Input files:

Output files:

Examples: