Detect Sources using Background from Smoothed Background Image

 

This is a sliding window source detection technique as the local source detection technique described in section 5.2.5. The image must be of the size 512 512 image pixels. Source counts are determined in the 3 3 pixels box from the image and the background counts in the same 3 3 pixels box from the (smoothed) background image. The command

DETECT/MAP dmpar edit

works from the parameter file dmpar.par (cf. Table 5.5). This parameter file can also be created (e.g. for the experiment ROSAT PSPC, pointing) with the command

  
Table 5.5: Parameter file for DETECT/MAP for ROSAT PSPC

CREATE/PARFIL EXDM dmpar ROSAT,PSPC.

• MISSION,DETECTOR is the experiment identifier. Allowed values are ROSAT,PSPC, ROSAT,HRI, and ROSAT,WFC.
• OBS_MODE is the observation mode. Allowed values are POINTING or SURVEY.  
• NUM_IMAGES is the number of images analysed with the map detection method. Up to 6 images can be analysed. The names of these images have to be given under the parameters IMAGE_1 to IMAGE_N, (N = NUM_IMAGES).
• IMAGE_1 is the name of the first, broad band (calibrated amplitude channel 7-256 in the default case, but the new recommended calibrated amplitude boundaries are 11-235).
• IMAGE_2 is the name of the second, soft band (calibrated amplitude channel 7-40 in the default case, but the new recommended calibrated amplitude boundaries are 11-41).
• IMAGE_3 is the name of the third, hard band (calibrated amplitude channel 41-256 in the default case, but the new recommended calibrated amplitude boundaries are 52-201).
• MIN_ML see description for Table 5.4
• MASK_FLAG see Table 5.4
• MASK see Table 5.4
• BG_IMAGE_1 name of first background image, broad band (calibrated amplitude channel 7-256, in the default case but the new recommended calibrated amplitude boundaries are 11-235).
• BG_IMAGE_2 name of second background image, soft band (calibrated amplitude channel 7-40 in the default case, but the new recommended calibrated amplitude boundaries are 11-41)
• BG_IMAGE_3 name of third background image, hard band (calibrated amplitude channel 41-256 in the default case, but the new recommended calibrated amplitude boundaries are 52-201)
• MDETECT_LIST_N is the name of the N-th source table coming from map detection, the N-th table contains the result of the detections of the N-th image IMAGE_N. In the default case the first, second and third table contain the results from the broad, soft and hard band.

There is an additional set of extended parameters which can be accessed either with WRITE/PARFIL or with CREATE/PARFIL using the extended option. For standard source detection they are not needed.

• NUM_RUNS is the number of compression runs. In each run the image is subsequently rebinned by a factor of 2. The image compression is done to allow to
  • map the point spread function which broadens as a function of off-axis angle (distance to the image center) in the pointing mode due to the telescope vignetting.
  • detect extended objects  
• DEAD_X_ROWS see description for Table 5.5
• DEAD_Y_ROWS see description for Table 5.5
• IMAGE_PRIORITY are the priorities assigned to the detections in the NUM_IMAGES bands (images). In the default case the priorities assigned to the broad, soft and hard bands are 32,8, and 2, respectively.
• BG_SCALE is the scaling factor of the background image. The default is 1 for EXSAS versions 96JAN and later (previously it was defaulted to 100).

In this parameter file three images IMAGE_1, IMAGE_2 and IMAGE_3 were specified and the name of a mask MASK to screen the image. The mask flag MASK_FLAG was set to F. The minimum maximum likelihood MIN_ML for detecting sources was set to 10. The names of the source tables MDETECT_LIST_1, MDETECT_LIST_2 and MDETECT_LIST_3 were chosen as the default values. The names of the background images are BG_IMAGE_1, BG_IMAGE_2 and BG_IMAGE_3. To the tables MDETCT_LIST_1, MDETCT_LIST_2 and MDETCT_LIST_3 are written the parameters of the detected sources, the source counts COUNT, the background counts per image pixel BACKG, the source x- and y-position in image pixels X_POS and Y_POS, the distance to the next source in image pixels SOURD and the distance to the next rib or edge in image pixels RIBD (cf. Table 5.29).

The number of compression steps NUM_RUNS, the values for the pixel ranges of the images (counted from the image boundary) where sources will not be looked for, DEAD_X_ROWS and DEAD_Y_ROWS, and the background map scaling BG_SCALE are set automatically to the default values for the ROSAT PSPC POINTING and SURVEY, ROSAT HRI, or ROSAT WFC case respectively, and have not to be specified explicitely. In case they really have to be changed, they can be accessed via WRITE/PARFIL or CREATE/PARFIL with the extended option.