UCL Department of Space and Climate Physics


SWIFT Known Issues


The initially released version of the catalogue (2015) was done with the IAU name (IAUNAME) source identifier "SWIFTUVOT" for each source, and was made available in that form. The decision was made to rename the catalogue sources and to include the catalogue version number. The IAU name for the sources is now UVOTSSC1.

Source Numbers: 

In some cases (0.03% of the sources overall) the distance to the nearest neighbour (filter_SRCDIST) is less than 1.5", which may seem unexpected when the matching of the sources uses a 1.5" radius. The reason for this discrepancy is that in the source matching an initial source position is found and other sources within 1.5" are matched with it.  Then an average position is found from this group, which may not be the same as the initial source position and can be shifted by a maximum of 1.5". The final distances between the sources therefore can be much less than 1.5".  

In addition, in a few instances multiple SOURCE IDs shared the same IAU name. They are now distinghuished by having a letter a,b,c,..etc. appended to their IAUNAME.  

Bright sources:

For very bright sources (over~90 counts per second, or mag<13 in the V filter) the catalogue tends to give a brighter magnitude than expected (by a few tenths of a magnitude). This is because of the way uvotdetect uses sextractor to measure the photometry, which is not so well suited to the nearly saturated sources as standard aperture photometry. See Photometry, magnitudes and fluxes in the Data Processing section. 

Data not included:

See Data Selection for information on what data has been intentionally excluded from the catalogue.