... (NVSS

http://www.cv.nrao.edu/nvss/

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... (SXSSC

http://xmm.vilspa.esa.es/external/xmm_data_acc/xsa/index.shtml

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... extracted

Details about determining the positional source error can be follow at: http://xmmssc-www.star.le.ac.uk/Catalogue/

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... Language

http://physics.nyu.edu/grierlab/idl_html_help/home.html

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... 2MASS

http://irsa.ipac.caltech.edu/cgi-bin/Gator/

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... (PIMMS

http://heasarc.gsfc.nasa.gov/docs/software/tools/pimms.html

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