XMM OM Catalogue - XMM-Newton

XMM-OM Serendipitous Ultraviolet Source Survey catalogue: SUSS5.0

XMM-OM-SUSS5.0 is a new 2020 release of the XMM OM Serendipitous Ultraviolet Source Survey catalogue. This release is largely an increment of the previous XMM-OM-SUSS4.1 release but includes flagging of sources affected by a patch of reduced sensitivity near the centre of the OM field of view.

The catalogue was compiled for the Optical Monitor instrument on board the ESA XMM Newton observatory. This version, the 5^th release of the catalogue, spans the period of observations from XMM-Newton revolution 34 (February 2000) to revolution 3704 (February 2020).

A refereed paper on the first version can be found in Page M.J. et al. (2012).

In addition to covering a larger observation period, this fifth release includes flagging of sources affected by a patch of reduced sensitivity near the boresight, caused by erroneously V-filter exposures during an observation of Jupiter in July 2017 (revolution 3224).

All data have been fully processed at the European Space Astronomy Centre (ESAC, Madrid, Spain) using the XMM Science Analysis Software (SAS) system version 18.0.

The number of observations (OBSIDs) included in the catalogue is 10,628.
The total number of entries in this release is 8,863,922. They correspond to 5,965,434 sources, of which 1,120,754 have multiple entries in the source table, corresponding to different observations.

The Catalogue is a FITS file consisting of two tables (please note that users wishing to use the TOPCAT tool to manipulate the catalogue, need to select the table format option, "FITS" to load the catalogue). The first one (SRCLIST) contains the sources, with positional and photometric data (count rate, magnitude and flux) and quality flags for each measurement. The content of the different columns (114) is:

In the second table (SUMMARY) we give a summary of the observations from which the sources have been detected and measured. The content of the columns (35) in this table is: 

The meaning of the quality flags (columns filter_QUALITY_FLAG and filter_QUALITY_FLAG_ST) in the SRCLIST table are as follows:

The columns filter_SKY_IMAGE indicate if a source has been detected in stacked (sky) images obtained with that filter. The catalogue contains 1,014,298 such detections, with 64,963 sources having multiple detections in different observations.

A cross-match of the whole catalogue with the GAIA DR2 data set, using a search radius of 3 arcsec gives 81% matches. Detections in the V filter have 89% matches. If we consider only detections with the best OM quality flag (0), we find 95% of OM catalogue detections have GAIA matches. The mean angular offset of the matches is 0.48 arcsecs. 90% of the matches lie within 0.87 arcsecs and 95% have separations < 1.05 arcsecs.

The XSA provides access to the OM Catalogue as a complete download of the file (~1.2 Gb, compressed fits format) as well as through a search interface whose results can be stored by the user in several formats. It should be noted that this interface allows the user to access only part of the information contained in the catalogue: source coordinates, magnitude and flux and their corresponding errors and quality flags. A reduced version of the complete catalogue (620 Mb, compressed fits format) can be downloaded as well.

The ESA-Sky utility allows the user to display the sources from the catalogue on top of sky images from different instruments at all wavelengths. This includes also images obtained with OM in two color combination, Visible (U, B and V OM filters) and UV (UVW1, UVM2 and UVW2 OM filters). It should be noted that OM images have a low dynamic range.

^* - see known issues

Known Issues and watchouts

• In around 1% of entries for detections, the seconds part of the RA component of the IAUNAME is erroneously rounded up to 60.0, or, similarly, the arcseconds part of the Declination component is rounded up to 60
• Flagging of detections is not foolproof. Problems can arise in crowded regions where sources may be contaminated by nearby objects but not always be flagged. Another cause is fields that contain a read-out streak caused by a bright star that lies outside the window - in these cases, sources detected along the read-out streak may have compromised parameters or even be spurious but not be flagged accordingly.
• In the case of very bright sources, the photometric data is nullified because the applied corrections for coincidence loss are high and not reliable. However, other quantities remain in the table, such as the major and minor axes, which may appear confusing to users
• A small number of detections are erroneously associated with another from the same observation. These arise when the source detection process identifies more than one detection within the image pixels associated with a single source. If spatially close enough, they may be erroneously assigned the same source number.
• Following the accidental observation of Jupiter by the OM in July 2017, a small region of the photocathode, near the centre of the OM field of view, has been damaged and has reduced sensitivity - this is referred to as the Jupiter patch (JP). Much of this region is currently identified via 'bad pixels' in the bad pixel calibration table, and sources that are detected within the bad pixel region are flagged as such in the catalogue. However, the region of reduced sensitivity is larger than that currently translated into the bad pixel map and sources in the shallow wings of the JP, beyond the mapped bad pixel area, are not flagged. In fact, the wings of the JP include the location of the pn boresight in the OM image (i.e. where sources (generally, XMM targets), placed at the pn boresight, appear within the OM field of view). The impact of the sensitivity loss at the pn boresight is filter-dependent but ranges from about 8% in the V filter, to around 3% in the UV filters (see CAL-TN-0019.pdf).
• Currently, detections that lie within the bad-pixel-marked area of the JP are identified via the 12^th flag element but this flag is also used to identify very bright sources. These two scenarios will be separately flagged for the next catalogue version. The absence of photometric values in the bright source cases, however, permits the cases to be distinguished in the current catalogue. For a very small number of cases (26), both situations apply and the numerical quality flag exceeds 4095.