Identification of the source (14 columns)

DETID (K)
A unique number which identifies each entry (detection) in the catalogue. The DETID numbering assignments in 4XMM-DR12 bear no relation to those in 3XMM-DR4 and earlier but the DETID of the matching detection from the 3XMM-DR4 catalogue to the 4XMM-DR12 detection is provided via the DR4DETID column.
SRCID (K)
A unique number assigned to a group of catalogue entries which are assumed to be the same source. The process of grouping detections in to unique sources has changed since the 2XMM catalogue series and is described in Section 3.8. The SRCID assignments in 4XMM-DR12 bear no relation to those in 3XMM-DR4 and earlier but the nearest unique sources from the 3XMM-DR4 catalogue to the 4XMM-DR12 unique source is provided via the DR4SRCID column
DR4SRCID (J)
The SRCID, from 3XMM-DR4, of the nearest unique source in that catalogue that lies within 10 arcsecs of the 4XMM-DR12 unique source position.
DR4DETID (J)
The DETID, from 3XMM-DR4, of the nearest detection in that catalogue that lies within 10 arcsecs of the detection position in 4XMM-DR12.
DR4DETDIST (E)
The distance, in arcsecs, between the 4XMM-DR12 detection position and the nearest detection (within 10 arcsecs) in the 3XMM-DR4 catalogue.
DR4SRCDIST (E)
The distance, in arcsecs, between the 4XMM-DR12 unique source position and the nearest unique source (within 10 arcsecs) in the 3XMM-DR4 catalogue.
DR4MULT (J)
The number of unique sources from the 3XMM-DR4 catalogue that lie within 10 arcsecs of the unique source position in 4XMM-DR12.
DR3SRCID (J)
The SRCID, from 2XMMi-DR3, of the nearest unique source in that catalogue that lies within 10 arcsecs of the 4XMM-DR12 unique source position.
DR3DETID (J)
The DETID, from 2XMMi-DR3, of the nearest detection in that catalogue that lies within 10 arcsecs of the detection position in 4XMM-DR12.
DR3DETDIST (E)
The distance, in arcsecs, between the 4XMM-DR12 detection position and the nearest detection (within 10 arcsecs) in the 2XMMi-DR3 catalogue.
DR3SRCDIST (E)
The distance, in arcsecs, between the 4XMM-DR12 unique source position and the nearest unique source (within 10 arcsecs) in the 2XMMi-DR3 catalogue.
DR3MULT (J)
The number of unique sources from the 2XMMi-DR3 catalogue that lie within 10 arcsecs of the unique source position in 4XMM-DR12.
IAUNAME (21A)
The IAU name assigned to the unique SRCID (see 3XMM-DR4 UG, Sec. 3.8.1 ).
SRC_NUM (J) SAS task srcmatch
The (decimal) source number in the individual source list for this observation; when expressed in the hexadecimal system it identifies the source-specific product files belonging to this detection (2XMM UG Appendix A.1).