Identification of the source (5 columns)

DETID (J)
A consecutive number which identifies each entry (detection) in the catalogue.
SRCID (J)
A unique number assigned to a group of catalogue entries which are assumed to be the same source. To identify members of the same group the distance in arcseconds between each pair of sources was compared on the three-sigma level of both positional errors. A maximum distance of 7" was assumed, which was reduced to 0.9 * DIST_NN (distance to the nearest neighbour) where necessary. See 2XMM UG, Sec. 3.2.3 a) and 2XMMi-DR3 UG, Sec. 3.2.1  for a more detailed description.
SRCID_2XMMi (J)
The unique source ID of the detection, DETID, in the 2XMMi catalogue. Due to the nature of the matching algorithm, some detections were re-assigned to a different source due to the presence of new detections, see 2XMMi-DR3 UG, Sec. 3.2  for a more detailed description.

This column replaces a similar column, SRCID_2XMM, in the 2XMMi catalogue that provided the SRCID mappings to 2XMM sources in that catalogue.

IAUNAME (21A)
The IAU name assigned to the unique SRCID (see 2XMMi-DR3 UG, Sec. 3.2.2 ).
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 (Appendix A.1).

Note that the columns, MATCH_1XMM, SEP_1XMM, SRCID_2XMMP, MATCH_2XMMP and SEP_2XMMP that were in the 2XMMi catalogue are removed in 2XMMi-DR3