The XMM-Newton Serendipitous Source Catalogue: 3XMM-DR6

User Guide to the Catalogue

Release 1.6 5th July 2016 Associated with Catalogue version 1.0

Prepared by the XMM-Newton Survey Science Centre Consortium

This User Guide refers directly to the full FITS and plain-text formats of the catalogue. Users interested in the details of changes to the data processing since the 3XMM-DR4 catalogue release, can refer directly to section 3. Information about the columns contained in the 3XMM-DR6 catalogue are presented in section 4. Brief summaries of some elements of the 3XMM-DR6 catalogue properties are provided in section 5 but a comprehensive evaluation of the catalogue is in Rosen, Webb, Watson et al., 2016, A&A, 590, 1.

Should you use the catalogue for your research and publish the results, please use the acknowledgement below and cite the paper describing 3XMM (Rosen, Webb, Watson et al., 2016, A&A, 590, 1).

This research has made use of data obtained from the 3XMM XMM-Newton serendipitous source catalogue compiled by the 10 institutes of the XMM-Newton Survey Science Centre selected by ESA.



3XMM-DR6 is the third generation catalogue of serendipitous X-ray sources from the European Space Agency's (ESA) XMM-Newton observatory, and has been created by the XMM-Newton Survey Science Centre (SSC) on behalf of ESA. It is an incremental release of the 3XMM catalogue and contains 1379 more observations and about 112718 more detections than the preceding 3XMM-DR5 catalogue, which was made public in April 2015.

The catalogue contains source detections drawn from a total of 9160 XMM-Newton EPIC observations made between 2000 February 3 and 2015 June 4; all datasets included were publicly available by 2016 January 31 but not all public observations are included in this catalogue. For net exposure time  ≥  1ksec, the total area of the catalogue fields is ~ 1750 deg2 but taking account of the substantial overlaps between observations, the net sky area covered independently is ~ 982 deg2.

The catalogue contains 678680 X-ray source detections above the processing likelihood threshold of 6. These X-ray source detections relate to 468440 unique X-ray sources, that is, a significant fraction of sources (128949, 19%) have more than one detection in the catalogue (up to 50 repeat observations in the most extreme case).

The catalogue distinguishes between extended emission and point-like detections. Parameters of detections of extended sources are only reliable up to the maximum extent measure of 80 arcseconds. There are 69276 detections of extended emission, of which 58073 are 'clean' (in the sense that they were not manually flagged) and 11066 comprise the 'cleanest' set where no flags are set and they are not in fields with high background levels.

Due to intrinsic features of the instrumentation as well as some shortcomings of the source detection process some detections are considered to be spurious or their parameters are considered to be unreliable. It is recommended to use either a detection flag or an observation flag (and, possibly, a high background flag) as filters to obtain what can be considered a 'clean' sample. There are 552991 out of 678680 detections that are considered to be clean (i.e., summary flag < 3).

For 149968 detections, EPIC spectra and time series were automatically extracted during processing, and a χ2-variability test was applied to the time series. 5238 detections in the catalogue are considered variable, within the timespan of the specific observation, at a probability of 10-5 or less based on the null-hypothesis that the source is constant. Of these, 3058 have a summary flag  < 3.

The median flux (in the total photon-energy band 0.2 - 12 keV) of the catalogue detections is ~ 2.4 × 10-14 erg/cm2/s; in the soft energy band (0.2 - 2 keV) the median flux is ~ 5.7 × 10-15, and in the hard band (2 - 12 keV) it is ~ 1.3 × 10-14. About 20% have fluxes below 1 × 10-14 erg/cm2/s. The flux values from the three EPIC cameras are, overall, in agreement to ~ 10% for most energy bands. The positional accuracy of the catalogue point source detections is generally < 3 arcseconds (90% confidence radius) and 90% of point sources have 1-sigma positional uncertainties  <  2.4 arcseconds.

1. Introduction

Pointed observations with the XMM-Newton Observatory detect significant numbers of previously unknown 'serendipitous' X-ray sources in addition to the proposed target. Combining the data from many observations thus yields a serendipitous source catalogue which, by virtue of the large field of view of XMM-Newton and its high sensitivity, represents a significant resource. The serendipitous source catalogue enhances our knowledge of the X-ray sky and has the potential for advancing our understanding of the nature of various Galactic and extragalactic source populations.

The 3XMM-DR6 catalogue is the eighth publicly released XMM-Newton X-ray source catalogue produced by the XMM-Newton Survey Science Centre (SSC) consortium. It follows the 1XMM (released in April 2003), 2XMMp (July 2006), 2XMM (August 2007), 2XMMi (August 2008), 2XMMi-DR3 (April 2010), 3XMM-DR4 (July 2013) and 3XMM-DR5 (April 2015) catalogues: 2XMMp was a preliminary version of 2XMM. 2XMMi and 2XMMi-DR3 are incremental versions of the 2XMM catalogue.

The 3XMM-DR6 catalogue is about 20% larger than the 3XMM-DR5 catalogue, which it supersedes. In terms of the number of X-ray sources, the 3XMM-DR6 catalogue is the largest ever produced. 3XMM-DR6 complements deeper Chandra and XMM-Newton small area surveys, probing a large sky area at the flux limit where the bulk of the objects that contribute to the X-ray background lie. The 3XMM-DR6 catalogue provides a rich resource for generating large, well-defined samples for specific studies, utilizing the fact that X-ray selection is a highly efficient (arguably the most efficient) way of selecting certain types of object, notably active galaxies (AGN), clusters of galaxies, interacting compact binaries and active stellar coronae. The large sky area covered by the serendipitous survey, or equivalently the large size of the catalogue, also means that 3XMM-DR6 is a superb resource for exploring the variety of the X-ray source population and identifying rare source types.

The production of the 3XMM-DR6 catalogue has been undertaken by the XMM-Newton SSC consortium in fulfillment of one of its major responsibilities within the XMM-Newton project. The catalogue production process has been designed to fully exploit the capabilities of the XMM-Newton EPIC cameras and to ensure the integrity and quality of the resultant catalogue through rigorous screening of the data.

The incremental part of the 3XMM-DR6 catalogue uses a slightly different pipeline to that which was used for 3XMM-DR5 and 3XMM-DR4. It is based on a pipeline (configuration 14.20_20150708_1030) that contains minor changes to the processing with respect to the previous 3XMM versions. It makes use of the SAS version 14 and the latest calibration files available at the time of the bulk reprocessing (October 2015). The changes made to the pipeline may have a very small impact on some of the parameters provided for the extra data used for 3XMM-DR6. The changes to the pipeline that may cause a small effect on the some of the data in the catalogue are that source spectra and light curves are now also created for pn Timing mode data, PN Small Window images are now included during the source detection procedure, and spectral and time-series products are also generated for sources detected within PN Small Window exposures, full sky view EPIC images are provided for Mosaic observations, energy-dependent CTI corrections, double-event energy correction and time- and pattern-dependent correction of the spectral energy resolution of EPIC-pn have been introduced, binning of MOS spectra has been changed from 15eV to 5eV and events flags are now filtered according to XMMEA_EM instead of XMMEA_SM. More information on these changes can be found here .

Users of the 3XMM catalogue should be aware that the DETID and SRCID values bear no relation to those in the previous 2XMM series of catalogues. However, a cross-matching is provided in 3XMM-DR6 via the DR3DETID and DR3SRCID columns.

2. User Guide for 2XMM

The extensive User Guide (UG) for the 2XMM catalogue still describes many of the details of the data processing and compilation approach applicable to the 3XMM-DR6 catalogue. However, a significant number of changes to the processing have been implemented for 3XMM and these are described in the 3XMM-DR4 user guide. For convenience, Table 1, which gives the energy band definitions, is repeated here.

Table 1:  Energy bands used in 3XMM-DR6 processing
Basic energy bands: 1 = 0.2 -   0.5 keV  
2 = 0.5 -   1.0 keV    
3 = 1.0 -   2.0 keV    
4 = 2.0 -   4.5 keV    
5 = 4.5 - 12.0 keV    
Broad energy bands: 6 = 0.2 -   2.0 keV   soft band, no images made
7 = 2.0 - 12.0 keV   hard band, no images made
8 = 0.2 - 12.0 keV   total band
9 = 0.5 -   4.5 keV   XID band

3.   3XMM-DR6 -- key changes with respect to 3XMM-DR5

3.1 Data selection

XMM-Newton observations considered for inclusion in the 3XMM-DR6 catalogue were those with ODFs available for processing up to 2015 June 4 and which had public release dates up to 2016 January 31. After allowing for a small number of observations which failed in processing for a variety of reasons, 9160 observations were available to make the 3XMM-DR6 catalogue. Table 2.1 gives the list of the final 9160 observations which are included in the 3XMM-DR6 catalogue.

3.2 Summary html pages

Summary html pages are provided for each detection. Links to the html summary pages of the other constituent detections of the unique source are embedded in the page. They can be accessed through the catalogue server. The slimline catalogue lists a column with the catalogue server URL which can be activated from within applications such as topcat.

3.3 Mosaic mode data

Most XMM-Newton observations are performed in pointing mode, where the spacecraft is locked on to a fixed position on the sky for the entire observation. Prior to XMM-Newton revolution 1812 (2009-Oct-30), a few special case observations were performed that involved attitude step changes during the observation, generally for the purposes of tracking a moving target. However, in the AO8 observing cycle, a specific mosaic observing mode was introduced in which the satellite pointing direction is stepped across the sky, taking snapshots at points (sub-pointings) on a user-specified grid. Data from dedicated mosaic mode or tracking (mosaic-like) observations are recorded into a single ODF for the observation.

In previous pipelines, the small number of mosaic-like observations sometimes produced products for a single sub-pointing only. This is because the pipeline filters data such that only events taken during an interval where the attitude is stable and centred on the nominal observation pointing direction (within a 3 arcmin tolerance), are accepted. Data from some, or all, of the other sub-pointings were thus sometimes excluded.

During 2012, the SOC devised a scheme whereby the parent ODF of a mosaic mode observation is split into separate ODFs, one for each mosaic sub-pointing. All relevant data are contained within each sub-pointing ODF and the nominal pointing direction is computed for the sub-pointing. This approach is applied to both formal mosaic mode observations and those mosaic-like/tracking observations executed before revolution 1812. For a mosaic mode observation, the first 8 digits of its 10-digit OBSID are common for the parent observation and its sub-pointings. However, while the last two digits of the parent observation OBSID almost always end in 01, for the sub-pointings they form a monotonic sequence, starting at 31. Mosaic mode sub-pointings are thus immediately recognisable in having OBSID values whose last two digits are  ≥ 31.

To the pipeline, mosaic mode (and mosaic-like) observation sub-pointings are transparent. No special processing is applied. Each sub-pointing is treated as a distinct observation. Source detection is performed on each sub-pointing separately and no attempt is made to simultaneously fit common sources detected in overlapping regions of multiple sub-pointings. While simultaneous fitting is possible, this aspect had not been sufficiently explored or tested during the preparations for 3XMM-DR6.

Some mosaic-mode observations were incorrectly split in to sub-pointings in previous 3XMM versions. Mosaic mode data has been reprocessed for inclusion in 3XMM-DR6, which should rectify previous problems. The observations for these reprocessed mosaic mode data are included in this list which also, inlcludes other observations that failed processing for previous versions of the catalogue. Mosaic mode observations are no longer included using the parent observation, but are now present as sub-pointings observations.

3.4 New naming convention for the DETID and the SRCID

To streamline the procedure for attributing the DETID number (which is unique to each detection) and the SRCID number (that is unique to each unique source) and to keep the same numbers from catalogue to catalogue, without providing supplementary columns in the catalogue with the DETID and SRCID from previous releases, starting in 3XMM-DR5 the numbering convention has been modified.

The OBSID which always remains the same for an observation is now coupled with the source number SRC_NUM to make the DETID. The SRCID attributed for a unique source is determined by using the first DETID attributed to that source (i.e. in the earliest observation that that source was detected).

This new naming convention is applied efficiently to pointing mode observations. However, some mosaic mode observations included in 3XMM-DR5 using the parent OBS_ID number (i.e. a number ending with 01 see Sec. 3.3) have been replaced in 3XMM-DR6 by their corresponding sub-pointings observations (i.e. same first 8 digits as the parent OBS_ID number but the last 2 digits are ≥ 31, Sec. 3.3). Consequently, following the new naming convention, DETID numbers built using the parent OBS_ID numbers in 3XMM-DR5 would have been replaced in 3XMM-DR6 by DETID numbers built using sub-pointings OBS_ID numbers. To avoid such modifications, the original DETID numbers built with the parent OBS_ID number for the first detection of a source during a given mosaic mode observation were kept. If a source is detected multiple times, due to overlapping regions of multiple sub-pointings, the subsequent DETID numbers are attributed normally.

However, for 36 source detections originally listed under the parent mosaic observation in 3XMM-DR5, no matching source detections could be found in the corresponding sub-pointings. This is due to the more accurate reprocessing of mosaic mode data for 3XMM-DR6 (see Sec. 3.3). Therefore, 36 DETID numbers of 3XMM-DR5 are absent in 3XMM-DR6 (the list is here).

Despite the new naming convention that aims at preserving SRCID numbers across catalogue versions, a certain number of SRCID numbers can disappear from one catalogue version to another. This is a consequence of the algorithm that groups detections together into unique sources. When new data is added and statistics is improved, the algorithm might find a better association of detections into unique sources. As a simple example, two detections initially considered as independent sources (therefore 2 distinct SRCID numbers) can be grouped together and considered as one unique source by the algorithm thanks to the inclusion of new detections in the area. Consequently, one SRCID number will disappear in the new version of the catalogue. A total of 355 SRCID listed in 3XMM-DR5 are absent 3XMM-DR6. The list can be found here

4. Catalogue content and organisation

This section summarises the organisation of the catalogue and gives details of all the columns. Known problems with parameters presented in the catalogue or with products associated with it are listed in Sec. 6.

There are 332 columns in the catalogue; they are grouped together and explained in the links below.

For each observation there are up to three cameras with one or more exposures which were merged when the filter and submodes were the same (2XMM UG, Sec. 2.2). The data in each exposure are accumulated in several distinct energy bands (Table 1). Camera-level measurements can further be combined into observation-level parameters. Consequently, the source parameters can refer to some or all of these levels: on the observation level there are the final mean parameters of the source (prefix 'EP'); on the camera level the data for each of the three cameras (where available) are given (prefix 'PN', 'M1', or 'M2'), and on the energy band level the energy-dependent details of the source parameters are given (indicated by a 'b' in the column name where b = 1,2,3,4,5,8,9). Finally, on a meta-level, some parameters of sources that were detected more than once (prefix 'SC') were combined, see 2XMM UG, Sec. 3.2.4.

The column name is given in capital letters, the FITS data format in brackets and the unit in square brackets. If the column originates from a SAS task, the name of the task is given to the right hand side and a link is set to the SAS package documentation with which the data in the 3XMM-DR6 catalogue was processed. It should be pointed out that the SAS used for the bulk reprocessing (for 3XMM(DR4 and DR5) was from manifest xmmsas_20121219_1645, which is based on SAS 12.0.1 but contains a number of SAS task upgrades that were required after the SAS 12.0.1 public release. The incremental part of the 3XMM-DR6 catalogue uses a slightly different pipeline to that which was used for 3XMM-DR5 and 3XMM-DR4. It is based on a pipeline (configuration 14.20_20150708_1030) that contains minor changes to the processing with respect to the previous 3XMM versions. A description of the column and possible cross-references follow.

Entries with NULL are given when no detection was made with the respective camera, that is, ca_MASKFRAC < 0.15 or NULL (i.e., a camera was not used in an observation).

Details of the columns:

Part 1: 14 columns: Identification of the source
This includes the basic static identifiers, IAU name, together with cross-references to the (spatially) nearest detection and source ID in the previous 3XMM-DR4 and 2XMMi-DR3 catalogues, where relevant, including information about the spatial displacements and the number of 'nearby' matches. Five new columns are used to provide this information.
Part 2: 11 columns: Details of the observation and exposures
Part 3: 20 columns: Coordinates
The external equatorial and Galactic coordinates and the internal equatorial coordinates as derived from the SAS tasks catcorr and emldetect are given together with the error estimates. Two columns convey information about the absolute astrometric catalogue used for field rectification and whether the field was successfully rectified
Part 4: 225 columns: Source parameters
The parameters of the source detection as derived from the SAS tasks emldetect and srcmatch are given here.
Part 5: 8 columns: Detection flags
This part lists the flags to qualify the detections. The summary flag, which gives an overall assessment for the detection, is followed by particular flags for each camera. A flag each is given if there exists at least one time series or one spectrum for this source. One column is added at the end of the catalogue to provide information about detections arising in fields with high background levels
Part 6: 13 columns: Detection variability
This part gives variability information for those detections for which time series were extracted. This includes six columns which provide measures of the fractional variance of the timeseries
Part 7: 41 columns: Unique source parameters
This part lists the source parameters for the unique sources across all observations (using the prefix 'SC'); these are coordinates, fluxes, hardness ratios, likelihoods, extent information and a variability and a summary flag. The number of detections is given also. Of six columns introduced for 3XMM, two of these relate to a fractional variance measure (and error). The other four provide information about the maximum and minimum measured fluxes from constituent detections (and errors). Two further columns relating to the epochs of the first and last observations contributing to a unique source, replace two columns in 2XMMi-DR3

Columns in the slimline catalogue:

Table 6 lists the 44 columns in the 3XMM-DR6 'slimline' version of the catalogue, all of which are explained in Part 1 or Part 7 of the 3XMM-DR6 column description, except the WEBPAGE_URL column which is described at the end of the table. These are the same 44 columns as in 3XMM-DR5.

5. Catalogue Properties

This section summarises the main properties of the catalogue but does not provide a detailed analysis. A comprehensive evaluation of the catalogue is presented in the 3XMM catalogue paper (Rosen, Webb, Watson et al., 2016, A&A, 590, 1).

5.1 Overview

The catalogue contains source detections drawn from 9160 XMM-Newton EPIC observations made between 2000 February 3 and 2015 June 4 and which were publicly available by 2016 January 31. Net exposure times in these observations range from < 1000 up to ~ 130000 seconds (that is, a full orbit of the satellite). Figure 5.2 shows the distribution of fields on the sky.

The total sky area of the catalogue observations with effective exposure > 1 ks is ~ 1750 deg2 which translates to ~982 deg2 when corrected for field overlaps.

The catalogue contains 678680 X-ray detections with total-band (0.2 -12 keV) likelihood values  ≥  6. These are detections of 468440 unique X-ray sources, that is, 128949 X-ray sources have multiple detections in separate observations (up to 50 detections). Of the 678680 X-ray detections, 69276 are classified as extended with 58073 of these being in regions considered to be 'clean' (SUM_FLAG  < 3).

5.2 Data quality

As part of extensive quality evaluation for the catalogue, each field has been visually screened. Regions where there were obvious deficiencies with the automatic source detection and parameterization process were identified and all detections within those regions were flagged (cf. 2XMM UG, Sec. 3.2.6 but importantly, note Section 3.11). Such flagged detections include clearly spurious detections (many of which are classified as extended) as well as detections where the source parameters may be unreliable. Each XMM-Newton field is also evaluated to assess the fractional area of the observation that is affected by flagged detections, as reflected by the OBS_CLASS parameter. For most uses of the catalogue it is recommended to use either a detection flag (SUM_FLAG, EP_FLAG or SC_SUM_FLAG) or an observation flag (OBS_CLASS) as a filter to obtain what can be considered a 'clean' sample.

Note that no attempt is made to flag spurious detections arising from statistical fluctuations in the background. An updated analysis of the false detection rate are presented in the 3XMM catalogue paper (Rosen, Webb, Watson et al., 2016, A&A, 590, 1).

5.3 Sensitivity and Photometry

Figure 5.4 presents, for each of the three cameras, the distributions of flux for energy bands 1 to 5 and also for the combined (EPIC) data. These give an indication of the limiting flux available in the catalogues for each of the bands.

Comparison of the detection count rates and fluxes in the 3XMM and previous 2XMMi-DR3 version shows good agreement between the two catalogues. A more detailed analysis of photometric issues are presented in the 3XMM catalogue paper (Rosen, Webb, Watson et al., 2016, A&A, 590, 1).

5.4 Astrometry

As noted in section 3.4 of the 3XMM-DR4 user guide, the 3XMM catalogue benefits from a number of improvements to the astrometry, several of which resulted from effects only discovered in the process of compiling the catalogue. The net effect for 3XMM source positions is a small improvement in the statistical position errors, a reduction in the position error systematics and increased confidence in the reliability of the position errors. A more detailed analysis of these issues are presented in the 3XMM catalogue paper (Rosen, Webb, Watson et al., 2016, A&A, 590, 1).

6. Known problems and other issues

Please read the Watchouts section of the 3XMM-DR6 catalogue page for the latest information on 3XMM-DR6 catalogue issues.

6.1 Problem cases

6.1.1 Spurious sources arising from MOS low energy noise

A significant number of observations have shown clear evidence of low energy noise affecting specific CCDs in the MOS cameras. Generally but not exclusively, it is CCD4 or CCD5 in MOS1 and CCD2 and CCD5 in MOS2 that are affected and the effect predominantly affects energies below 1keV (bands 1 and 2). Affected CCDs often stand out in the MOS images as having notably higher count levels compared to the adjacent CCDs. Of itself, this increased noise primarily leads to reduced sensitivity in the relevant CCD sky area.

However, a further significant impact arises in source detection because the computation of the background map (see 2XMM UG, Sec. 3.1.2d) does not adequately cope with the step transition in the brightness level between the noisy CCD and adjacent CCDs. The result can be an over- or under- representation of the background map in the vicinity of the CCD boundary and this can then lead to the detection of spurious (often extended) sources near the edges of the noisy CCD where it borders another CCD. These sources generally receive a manual flag from the visual screening process (see 2XMM UG, Sec. 3.2.6, and the changes discussed in Section 3.11, user guide for 3XMM-DR4) but users should be aware of the issue.

6.1.2 Reduced sensitivity due to high background

The optimised flare filtering process generally results in greater sensitivity to sources. However, in some circumstances, the reverse can occur. About 200 fields that are present in both 3XMM-DR6 show higher backgrounds in the EPIC images, and fewer detections, in the 3XMM-DR6 data. This arises because occasionally, one or more instruments can have a persistent high background while the other instruments have a lower background count rate. In previous processing the high background instruments were generally excluded from the source detection stage because, after applying the flare GTI filtering, less than 1ksec of data remained.

In the processing for 3XMM, the optimised flare filtering process determines an optimum background threshold, even if the count rate is persistently high. This may then leave significant apparently usable exposure with a high count rate. As such, instruments showing a persistently high background can still be included in the source detection stage and, even when combined with lower background data from the other instruments, can lead to reduced, rather than increased sensitivity.

6.1.3 Exposure correction failure for timeseries

In previous catalogues, a few cases have been noted where the detection shows a variability that is due to incorrect handling of the data. Two reasons have been considered responsible:

6.1.4 Timeseries not corrected to on-axis position

EPIC timeseries are provided to the public as XMM-Newton pipeline-processed products (filetype SRCTSR), for detections in EPIC exposures that were used in source detection. In this process, the timeseries of the source region and background region (see section 3.6 of the 3XMM-DR4 user guide) are fed in to the SAS task, lccorr_pcms, to generate a background-subtracted, exposure-corrected timeseries. lccorr_pcms applies several corrections to take account of aspects such as exposure differences between CCDs. However, while the task can correct for the off-axis dependence of vignetting (e.g. see section of the XMM-Newton User handbook), this correction is not applied to timeseries in the products from the bulk reprocessing that was used for the 3XMM-DR4 catalogue. This was also the case for the 2XMM series of catalogues.

A consequence of not applying this vignetting correction is that the absolute mean count-rate of the timeseries is generally not equivalent to that of the source being observed in the on-axis position. Thus if a user compares two or more timeseries of a common, constant object, observed at very different off-axis angles in separate observations, they will find discrepancies in the mean levels of the timeseries due to the lower effective area pertinent to detections at larger off-axis angles.

To make a more accurate comparison of such timeseries, they should be corrected to the on-axis position. To do this, one can compute an approximate constant scaling factor that can be applied to the pipeline product timeseries (filetype=SRCTSR), for example, via the ftool, farith, by obtaining a measure of the vignetting factor at the source position.

6.2 Other issues

6.2.1 New calibrations and fluxes

A number of improvements in the calibration of the MOS and pn have occurred which lead to slight changes in the Energy Conversion Factors (ECFs) (see here for information on the EPIC response files) that are used for converting EPIC band count rates to fluxes. Of note is the fact that MOS redistribution matrices are now provided for 13 epochs and for three areas of the detector that reflect the so-called 'patch', 'wings-of-patch' and 'off-patch' locations.

For 3XMM-DR5 a simple approach has been adopted. ECFs were computed following the prescription of Mateos et al. (2009), for energy bands 1-5 and band 9, for full-frame mode, for each EPIC camera, for each of the Open, Thin, Medium and Thick filters. For pn, the ECFs are calculated at the on-axis position. The pn response is sufficiently stable that no temporal resolution is needed.

For MOS, to retain a direct connection between the ECFs and publicly available response files, the ECFs used are taken at epoch 13 and are for the 'off-patch' location. The latter choice was made because the large majority of detections in an XMM-Newton field lie outside the 'patch' and 'wings-of-patch' regions, which only relate to a region of radius  ≤  40 arcseconds, near the centre of the field. The use of a single epoch (epoch 13) was made to retain simplicity in the processing and because the response of the MOS cameras exhibits a step function change between epochs 5 and 6, with different but broadly constant values either side of the step. None of the 13 calibration epochs represent the average response and thus no response file exists to which average ECFs can be directly related. The step-function change in the responses for MOS is most marked in band 1 (0.2-0.5 keV) for the 'patch' location, where the maximum range in ECFs either side of the step amounts to 20%. Outside the 'patch' region, and for all other energy bands, the range of the ECF values with epoch is  ≤  5% and is  ≤  2.5% for the 'off-patch' region. Epoch 13 was chosen, somewhat arbitrarily, as being typical of epochs in the longer post-step time interval.

The ECFs, in units of 1011 cts cm2/erg, adopted for 3XMM-DR6, are provided in Table 8, for each camera, energy band and filter. The camera rate and flux are related via

ca_FLUX = (ca_RATE   / ECF )

Table 8: Energy Conversion Factors used for converting EPIC band count rates to fluxes in 3XMM-DR6
Camera Band Open Thin Medium Thick
PN 1 16.9783 9.5248 8.3696 5.1065
2 10.0696 8.121 7.8681 6.0479
3 6.1551 5.867 5.7673 4.9893
4 1.9844 1.9527 1.929 1.8282
5 0.5782 0.5774 0.5764 0.5698
9 5.098 4.5586 4.4602 3.7636
MOS-1 1 3.0896 1.7345 1.5258 0.9977
2 2.1152 1.7461 1.6974 1.3792
3 2.1387 2.0407 2.0058 1.7871
4 0.7491 0.7375 0.7292 0.6991
5 0.1452 0.145 0.1451 0.143
9 1.5035 1.3843 1.3584 1.2035
MOS-2 1 3.1094 1.7336 1.5223 0.9907
2 2.1309 1.7572 1.7082 1.3869
3 2.1407 2.0426 2.0079 1.7887
4 0.7531 0.7418 0.7333 0.703
5 0.1528 0.1528 0.1524 0.1502
9 1.5097 1.3894 1.3634 1.2076

Note that canned response matrices for basic XMM-Newton spectral analyses can be obtained from here.

6.2.2 High proper motion objects

No epoch information is used when matching detections to construct unique sources. As a consequence, detections of high proper motion stars from multiple observations spanning a significant period of time may not have been matched into a single unique source in the catalogue. A good example is 61 Cyg whose proper motion (~ 5 arcseconds/year) between observations from the earliest XMM-Newton revolution (539) in 3XMM-DR5 to the latest (2269) translates in to a shift in position of more than 45 arcseconds between the first and last observations. The detections of the stellar component at higher declination are mapped to two distinct unique sources due to its movement (i.e. 3XMM J210655.9+384516 and 3XMM J210657.4+384527) - the component at lower declination is grouped in to 3 unique sources. However, the more relaxed criteria for recognising potential confusion result in it being flagged as CONFUSED, the confusion arising from positional overlaps with other detections of itself.


Budavari, T & Szalay, A 2009, Ap.J, 679, 301-309 Probabilistic Cross-Identification of Astronomical Sources

Edelson, R., et al. 2002, Ap.J, 568, 610-626 X-Ray Spectral Variability and Rapid Variability of the Soft X-Ray Spectrum Seyfert 1 Galaxies Arakelian 564 and Ton S180

Mateos, S., et al. 2009, A&A, 496, 879-889 Statistical evaluation of the flux cross-calibration of the XMM-Newton EPIC cameras

Pye, J., et al. 1995, MNRAS, 274, 1165-1193, The ROSAT Wide Field Camera all-sky survey of extreme-ultraviolet sources - II. The 2RE Source Catalogue

Read, A., et al. 2011, A&A, 534, A34 A new comprehensive 2D model of the point spread functions of the XMM-Newton EPIC telescopes: spurious source suppression and improved positional accuracy

Rosen, S.R., Webb, N.A., Watson, M.G., et al. 2016, A&A, 590, 1 The XMM-Newton serendipitous survey. VII. The third XMM-Newton serendipitous source catalogue

Vaughan, S., et al. 2003, MNRAS, 345, 1271-1284 On characterizing the variability properties of X-ray light curves from active galaxies

Watson, M., et al. 2009, A&A, 493, 339-373 The XMM-Newton serendipitous survey. V. The Second XMM-Newton Serendipitous Source Catalogue

Document revision history

Release No. Release Date      Comments
1.0 23 July 2013 First release
1.1 24 July 2013 Added section 3.12 and fixed minor typographic corrections
1.2 02 August 2013 Section 6.1.4 added. Reference added. Some SAS task links ammended. Links to CCF and SAS tasks provided in A.2
1.3 30 August 2013 Added link to watchouts in section 6.
1.4 15 September 2013 Added units and flux-rate conversion formula in section 6.2.1.
1.5 April 2015 Revised version for 3XMM-DR5
1.6 July 2016 Revised version for 3XMM-DR6


A.1 List of the observations used in the catalogue

List of observations ('fields').