Last modified: 24 October 2019


Master Source Polygon Region File (poly3.fits)

The polygon file consists of a single FITS format region file for each master source tracing an extended source of X-ray emission. The file contains a single convex hull polygon.

The master source polygonal region FITS file is named: 〈m〉N〈v〉_poly3.fits

where 〈m〉 is the Master Source name—formatted as "2CXOJhhmmsss{p|m}ddmmssX]"— and 〈v〉 is the data product version number.

Since CXC FITS region files are stored in SKY coordinates, that is the POS column is in SKY rather than World Coordinates, a single stack - from those that overlap the source - has been selected to define this mapping. This stack is stored in the BASE_STK keyword of the file. A consequence of this is that this poly3 file can only be used to filter the BASE_STK event file, or any observation event file that forms this stack.

Files will be available soon

The poly3 files for the master convex-hull sources are currently not available from CSCView. They will be made available with a future update to CSCview, which should be soon.


An example master-source poly3 file from release 2.0 is:

unix% dmlist 2CXOJ2200526p205828XN020_poly3.fits blocks
Dataset: 2CXOJ2200526p205828XN020_poly3.fits
     Block Name                          Type         Dimensions
Block    1: PRIMARY                        Null        
Block    2: POLY3EXT3                      Table         3 cols x 1        rows

which has columns:

unix% dmlist 2CXOJ2200526p205828XN020_poly3.fits cols
Columns for Table Block POLY3EXT3
ColNo  Name                 Unit        Type             Range
   1   POS(X,Y)[14]         physical     Real8(14)      -Inf:+Inf            Physical coordinate
   2   COMPONENT                         Int4           -                    component
   3   SHAPE                             String[7]                           Region shape
World Coord Transforms for Columns in Table Block POLY3EXT3
ColNo    Name
1:    eqpos(ra_src ) = (+330.2115)[deg] +TAN[(-0.000136667)* (POS(X)-(+4096.50))]
           (dec_src)   (+20.9065 )           (+0.000136667)  (   (Y) (+4096.50)) 

The stack that defines the SKY to Celestial coordinate mapping is given by the BASE_STK keyword:

unix% dmkeypar 2CXOJ2200526p205828XN020_poly3.fits BASE_STK echo+

The event file for this stack can be filtered using the poly3 file as a region file, using the standard DM region-filter syntax - for example:

unix% dmcopy "acisfJ2200507p205423_001N020_evt3.fits[sky=region(2CXOJ2200526p205828XN020_poly3.fits)][bin sky=8]" chs.fits

The dmmakereg tool can be used to convert the region into ASCII format; for example:

unix% dmmakereg "region(2CXOJ2200526p205828XN020_poly3.fits)" sky.reg kernel=ascii
unix% cat sky.reg
# Region file format: DS9 version 4.1
global color=blue dashlist=8 3 width=1 font="helvetica 10 normal roman" select=1 highlite=1 dash=0 fixed=0 edit=1 move=1 delete=1 include=1 source=1
Polygon(3790.5,4618.5,3814.5,4474.5,3910.5,4350.5,3974.5,4330.5,4058.5,4314.5,4154.5,4338.5,4254.5,4426.5,4302.5,4582.5,4314.5,4650.5,4186.5,4854.5,4066.5,4862.5,3962.5,4862.5,3842.5,4774.5,3790.5,4618.5) #  

A region file in celestial coordinates (Right Ascension and Declination) can also be created using dmmakereg, although it requires a little-more work:

unix% dmmakereg "region(2CXOJ2200526p205828XN020_poly3.fits[cols ra_src,dec_src,shape,component])" outfile=- kernel=ascii | sed -e 's/^physical/fk5/' > cel.reg

This can then be used with any FITS file with a World-Coordinate system (not just those which match the BASE_STK coordinate system), for example a 2MASS data set:

unix% ds9 2mass.fits -region cel.reg

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