XMM-Newton Science Analysis System


catcorr (catcorr-0.11.2) [xmmsas_20230412_1735-21.0.0]

Comments

The catcorr task is believed to be a modest improvement on eposcorr in the following respects:

• catcorr uses three reference catalogues, instead of just USNO. The 2MASS infra-red positions are mostly useful at very low galactic latitudes. In parts of the sky covered by the Sloan Digital Sky Survey (SDSS) it has much superior sensitivity and hence a larger number of X-ray counterparts.

• catcorr uses an iterative function optimisation algorithm to find the best fit, whereas eposcorr evaluated the fit on a relatively coarse grid of positions shifts and rotations, which resulted in some quantisation of the resulting values.

• catcorr attempts to detect and ignore certain image artefacts and so is able to find a reasonable cross-match in some cases when eposcorr could not.

• catcorr uses the positional error estimates provided in the reference catalogues which eposcorr did not (because it relied upon WCStools for access to catalogue data). In the case of USNO it also uses proper motion values which can be significant for nearby stars, especially when the epoch of the reference catalogue differs significantly from the date of the XMM observation.

The result is that whereas eposcorr was able to find improved positions in about 60% of fields, the success rate of catcorr is close to 85%.