3XMM-DR4, watchout number 3

                Erroneous error values in 3XMM-DR4 catalogue

Whilst the 3XMM-DR4 catalogue values have been shown to be robust, due
to an unitialised variable in a subroutine of the source detection
chain, a subset of the error values in the current version of the
3XMM-DR4 catalogue have been over-estimated, and a very small portion
of these errors have been under-estimated. Only when a quantity is
based on an error-weighted combination of values, such as the EPIC
(EP) columns, are the non-error values affected.  The quality of the
catalogue is therefore assured, but the overall accuracy is in general
better than that which is given in the current version. 

The error values affected are for the counts, the rate, the flux, the
hardness ratio and the position. The worst affected column is the
error on the EPIC band 9 flux (EP_9_FLUX_ERR) where 10% of the errors
are erroneous, some (~0.1%) by more than a factor 1000. Other columns are in
general much less affected, with less than 2% of the errors showing
erroneous values in many cases.  The RA/dec errors (RADEC_ERR) are
erroneous for about 1.4% of detections, with 80% of those values
deviating  by  < +/- 0.1 arcsecs.  Work is being carried out to rectify
the problem. However, until a new version can be produced, the columns
affected by this bug are: 

RADEC_ERR
EP_?_FLUX_ERR
PN_?_FLUX_ERR
M1_?_FLUX_ERR
M2_?_FLUX_ERR
EP_?_RATE_ERR
PN_?_RATE_ERR
M1_?_RATE_ERR
M2_?_RATE_ERR
EP_8_CTS_ERR
PN_8_CTS_ERR
M1_8_CTS_ERR
M2_8_CTS_ERR
EP_HR#_ERR
PN_HR#_ERR
M1_HR#_ERR
M2_HR#_ERR
EP_EXTENT_ERR
SC_*_ERR

(key: ? implies bands 1, 2, 3, 4, 5, 8 and 9; # implies hardness ratios 1, 2, 3 and 4 and * means all columns starting with SC_ and finishing _ERR)

Users working on individual sources can re-run the source detection on their fields of interest with SAS 14 tasks which will be released in November 2014.