All Source Detection Done with one Command

 

In sections 5.2.5, 5.2.6, and 5.2.8 the local, map and maximum likelihood source detection was described. It is possible to perform all three detections in one EXSAS command:

DETECT/SOURCES image pem [mask] [displ] [minml] [skycen,bin]
               [offmax] [bg_image]

 

• image is the name of the image. It must be of size 512 512 pixels and one pixel must be about half of the size of the FWHM of the on-axis point spread function. The image must contain the general EXSAS descriptors. If image is set to create, then an image with the name image1.bdf will be created. The x,y sky coordinates of the image center must then be given in the parameter skycen and the bin size in sky pixels in the parameter bin. An image fulfilling these requirements can also be created by the command CREATE/SOURCE_DETECT_IMAGE.
• pem is the name of the small map sorted photon event table. This table contains the photon information to be analysed by the maximum likelihood technique. This table is also used to create the image. A PEM can be created from a PET by the command MAKE/PEM.
• mask is the name of the mask image to screen the image. It is a R*4 image with 0. or 1. intensity per image pixel. This mask can be created by one of the commands CREATE/MASK, CREATE/WOBBLED_MASK (PSPC only), or ADJUST/MASK. If set to create, then it can be created by cursor input from the displayed image. The default is a circular mask with a radius of 57 arcmin for ROSAT,PSPC, EXSAS_CAL:mask057.bdf, and EXSAS_CAL:mask0_hri.bdf for ROSAT,HRI. For ROSAT PSPC a mask image containing the struts of the window support structure, EXSAS_CAL:mask0thick.bdf, can also be used. This image has to be adjusted by the command ADJUST/MASK (see section 5.2.35).

  Alternatively to this method the command CREATE/WOBBLED_MASK can be used (see section 5.2.35) to obtain a mask including the window support structure and corrected for spacecraft wobble.

• displ is a display flag. If set to displ then the positions of the found sources will be displayed into the overlay channel of the displayed image. The default is nodisplay.
• minml is the minimum maximum likelihood (ln(1-probability of existence) of a source. The default is 10.
• skycen,bin with skycen is the x,y coordinate of the image center in sky pixels and bin is the bin size of the image in sky pixels. For ROSAT,PSPC (pointing) the default is 0.,0.,30, for ROSAT, HRI the default is 0.,0.,10., and for ROSAT,PSPC (survey) 0.,0.,192. This parameter becomes active in case the parameter image is set to create.
• offmax is the maximum off-axis-angle in arc minutes. The default is 57 for PSPC, 20 for HRI. Up to this angle sources are analysed in the ML algorithm.
• bg_image is the name of the background image, the default is create to create the background image by the command CREATE/BG_IMAGE.

Examples:

DETECT/SOURCES image1 events
DETECT/SOURCES image1 events   ?   ?     10.
DETECT/SOURCES image1 events   ? displ   10.
DETECT/SOURCES image1 events   ?   ?     10.  ?   20.
DETECT/SOURCES image2 events2 mask displ 15.
DETECT/SOURCES create events   ?   ?     8.  0.,0.,15. 60.
DETECT/SOURCES create events   ?   ?     8.  0.,0.,15. 60. bg