A source list, which at minimum must contain a table extension named SRCLIST with the following columns:
- (mandatory) RA: right ascension of the source in decimal degrees.
- (mandatory) DEC: declination of the source in decimal degrees.
- (optional) SCTS: total source counts; mandatory only if radiusstyle=`contour'.
- (optional) BG_MAP: total background counts per pixel; mandatory only if radiusstyle=`contour'.
- (optional) ID_INST: integer id of the EPIC instrument; mandatory only if radiusstyle is not equal to `userfixed'.
- (optional) ID_BAND: integer id of the energy band; mandatory only if radiusstyle is not equal to `userfixed'.
- (optional) a further column, specified by srcidcol, which should contain a unique source identifying integer; mandatory only if operationstyle=`batch'.
If radiusstyle=`contour', the source list should also contain WCS keywords so as to enable one to convert the flux-per-pixel background values to flux-per-arcsec. XMM EPIC source lists currently store these in a slightly non-standard way, as keywords in the table header, instead of as image-position column keywords. Since the major grist to region's mill is EPIC source lists, the task has been `hard-wired' to look for these header keywords. These keywords are described as follows:
- TCTYPEn: ='RA—TAN' for n=1 and 'DEC–TAN' for n=2.
- TCRPIXn: the position in pixel units of the reference point.
- TCRVALn: the position in world (ie, RA or dec) units of the reference direction.
- TCDELTn: the size of the pixels in world (ie, RA or dec) units. Note that for RA/dec as world units, the n=1 pixel size is usually made negative, so that RA increases to the left.
- TCROTA2: the rotation angle of the world frame. Usually this rotation is zero and in this case the keyword can be omitted.
`n' in the above should run from 1 to 2.
I realize that this is a very narrow and restrictive source-list format definition. In future it is hoped to be able to make region
accept much more generic lists of sources.
