The XMM-Newton Serendipitous Source Catalogue: 2XMMi-DR3

User Guide to the Catalogue

Release 1.0 28 April 2010 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 the data processing can refer directly to section 2 and using the link from there to the 2XMM User Guide. Users interested in the main properties of the catalogue will find the summary and sections 1 & 5 of most immediate interest.



2XMMi-DR3 is the latest increment of the second 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. The catalogue has 836 more observations and about 64000 (22%) more detections than the preceding 2XMMi catalogue, which was made public in August 2008. The processing used to generate the 2XMMi-DR3 catalogue is essentially the same as used for 2XMM and 2XMMi and is based on the pipeline developed for the re-processing of all XMM observations conducted in 2006/7.

The catalogue contains source detections drawn from a total of 4953 XMM-Newton EPIC observations made between 2000 February 3 and 2009 October 08; all datasets included were publicly available by 2009 October 31 but not all public observations are included in this catalogue. The total area of the catalogue fields is ~ 814 deg2, but taking account of the substantial overlaps between observations, the net sky area covered independently is ~ 504 deg2.

The catalogue contains 353191 X-ray source detections above the processing likelihood threshold of 6. The 353191 X-ray source detections relate to 262902 unique X-ray sources, that is, a significant fraction of sources (41979) have more than one detection in the catalogue.

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 30470 detections of extended emission, of which 5770 are 'clean' (i.e., have not received a manual flag).

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 as a filter to obtain what can be considered a 'clean' sample. There are 284270 out of 353191 detections that are considered to be clean (i.e., summary flag < 3), and 2318 out of 4953 fields are considered to have no or at most a couple of spurious detections in them (observation class < 2).

For 56017 detections spectra and time series were automatically extracted during processing, and a χ2-variability test was applied to the time series. 3177 detections in the catalogue are considered variable at a probability of 10-5 or less based on the null-hypothesis that the source is constant.

The median flux (in the total photon-energy band 0.2 - 12 keV) of the catalogue detections is ~ 2.5 × 10-14 erg/cm2/s; in the soft energy band (0.2 - 2 keV) the median flux is ~ 5.6 × 10-15, and in the hard band (2 - 12 keV) it is ~ 1.4 × 10-14. About 20% have fluxes below 1 × 10-14 erg/cm2/s. The positional accuracy of the catalogue point source detections is generally < 5 arcseconds (99% confidence radius). The flux values from the three EPIC cameras are, overall, in agreement to ~ 10% for most energy bands.

Though the 2XMMi-DR3 catalogue is a catalogue of serendipitous sources, the observations from which it has been compiled are pointed observations with one or more targets. An analysis to identify the target of each observation and to classify the contents of the field with regard to its serendipity has been carried out. In about 64% of the cases, one or (occasionally) more detections could be directly identified with the target(s) of the observations.

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

With this increment catalogue, for the first time, as part of the catalogue naming convention we introduce the concept of a data release (DR) as a means of distinguishing between increments - see version definitions. In this scheme, 2XMM is considered as DR1, 2XMMi as DR2 and the present catalogue as DR3.

The 2XMMi-DR3 catalogue is about 22% larger than the 2XMMi catalogue, which it supersedes, due to the ~1.5-year longer baseline of observations included. As such, it is the largest X-ray source catalogue ever produced, containing more than twice as many discrete sources as either the ROSAT survey or pointed catalogues. 2XMMi-DR3 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 2XMMi-DR3 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 2XMMi-DR3 is a superb resource for exploring the variety of the X-ray source population and identifying rare source types.

The production of the 2XMMi-DR3 catalogue has been undertaken by the XMM-Newton SSC consortium in fulfilment of one of its major responsibilities within the XMM-Newton project. The catalogue production process has been designed to exploit fully 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 earlier 2XMM catalogue was made from a subset of public observations emerging from a re-processing (in 2006/7) of all XMM observations made prior to that point. The first increment, 2XMMi, included a further 626 observations. These came from a) observations from the re-processing that had been proprietary at the time of the 2XMM release but which subsequently became public before 01 May 2008 and b) 90 observations that had been processed as part of the routine, day-to-day XMM data processing performed by the SSC, after the 2006/7 re-processing and which were also public at 01 May 2008. The processing pipeline used for the latter was essentially identical to that used for the re-processing.

The new 2XMMi-DR3 catalogue augments the 2XMMi data with a further 836 observations, 89 of which come from the 2006/7 re-processing and were public by 31 October 2009. The bulk of the extra data are from suitable observations from the more recent routine day-to-day pipeline processing operations which were also public by 31 October 2009. It should be noted that 14 observations (675 detections) in the 2XMMi-DR3 catalogue come from day-to-day processings performed since 15 April 2009 using a pipeline in which newer energy conversion factors (ECFs) are used in converting count rates to fluxes than were used for 2XMM/2XMMi (see Sec 6.2.1 and Sec 6.2.2 ). The largest change in ECF is approximately 8% and affects the MOS1 and MOS2 band 1 fluxes when observing with the THICK filter. Otherwise the changes in the ECFs are < 5%.

Users of the 2XMMi-DR3 catalogue should note that every detection in 2XMM and 2XMMi appears in 2XMMi-DR3 with the same detection identifier, DETID. New detections have DETID values > 289084. In general the 2XMM and 2XMMi unique source identifiers, SRCID, have also been preserved but in a small number of cases, detections from 2XMM or 2XMMi sources were regrouped and, in rare cases (essentially restricted to complex regions), sources from 2XMM or 2XMMi no longer appear in 2XMMi-DR3, being replaced by new sources comprised of different arrangements of detections (see Sec 3.2). Since detections can occasionally be allocated to a different source in the 2XMMi-DR3 catalogue, earlier SRCID values can disappear but they are not reallocated so that gaps in the SRCID sequence can occur. The 2XMMi-DR3 catalogue provides information that indicates where changes have occurred.

2. User Guide for 2XMM

The extensive User Guide (UG) for the 2XMM catalogue describes all the details of the data processing and compilation of the catalogue. As with 2XMMi, the 2XMMi-DR3 catalogue processing is practically unchanged. In the following section the differences or updates for the 2XMMi-DR3 catalogue with respect to 2XMMi are described. For convenience, Table 1, which gives the energy band definition, is repeated here.

Table 1:  Energy bands used in 2XMM, 2XMMi and 2XMMi-DR3 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. 2XMMi-DR3 -- differences and additions with respect to the 2XMMi catalogue

3.1 Data selection

The selection of XMM-Newton observations for inclusion in the 2XMMi-DR3 catalogue follows the same guidelines as for the 2XMM and 2XMMi catalogues but with a new cut-off for the public release date: All observations that have a public release date prior to 2009 October 31 were eligible for inclusion. Table 2.1 gives the list of the final 4953 observations (3491 from 2XMM, 626 from 2XMMi and 836 new) which are included in the 2XMMi-DR3 catalogue.

3.2 Unique celestial sources

The details of the procedure used for matching detections in to unique sources on the sky is described in the 2XMM UG, Sec. 3.2.3 a). For 2XMMi, essentially the same process was adopted, albeit with a small correction but it was necessary to consider the impact of merging the new detections available for 2XMMi with the ones already in 2XMM. This was explained in the 2XMMi UG, Sec. 3.2.1 a). As noted above, occasionally this process can result in a change of the unique source to which a previous detection is allocated. For 2XMMi-DR3 we have adopted essentially the same mechanism for merging detections, allowing the detections to be grouped from scratch. However, we describe below some alterations to the way in which such changes are flagged in the 2XMMi-DR3 catalogue.

3.2.1 Re-matching and representation of changes

The process of finding the set of detections which appear to come from the same source and thus have a single SRCID number is simple and unambiguous in most of the sky. However, in a few areas, for example in ridges of extended emission or in shells around SNRs, the detection-matching process produces results which are occasionally unstable in the sense that minor changes to the parameters of the algorithm produce slightly different matches.

In addition, the inclusion of new detections in the catalogue can lead to cases where previous sources can be coalesced or a single course can fragment. In either case, or in cases where a new detection simply joins an existing unique source, the parameters of the unique source can be modified.

In 2XMMi, two flags were introduced, SC_CHFLAG1 and SC_CHFLAG2, to signify the detailed nature of such changes. In 2XMMi-DR3 this useful but somewhat complicated flagging scheme is replaced by a simpler concept. In 2XMMi-DR3, we utilize the following two flags,

i) SC_DR_FIRST signifies the data release of the catalogue in the 2XMM series in which the source with this SRCID first appeared (DR1 represents 2XMM, DR2 represents 2XMMi and DR3 represents 2XMMi-DR3). Note that where SC_DR_FIRST = DR1, the IAU name retains the 2XMM prefix (Sec 3.2.2). Where SC_DR_FIRST = DR2 the IAU name prefix is 2XMMi and it is also 2XMMi when SC_DR_FIRST = DR3.
ii) SC_DR_LAST signifies the data release of the catalogue in the 2XMM series in which the source with this SRCID was last updated in any way.

In 2XMMi-DR3 we also introduce another new flag which indicates where there is uncertainty about which unique source a detection is assigned to. The CONFUSED flag is set true for a unique source if any detections that comprise it overlap with another unique source. This is taken to be the case if the 3 sigma positional error (3 * POSERR) of the detection overlaps the corresponding 3 sigma positional error of any other unique source (which is located within 7 arc-seconds of it).

Note that the only changes in the catalogue parameters refer to the unique source identification (SRCID), source (SC_*) parameters and IAUNAME. All parameters referring to an observation or a detection remain unchanged.

A consequence of the fact that detections can be re-grouped during the matching procedure is that 170 sources in 2XMMi do not appear in 2XMMi-DR3 and 438 sources from 2XMM are absent from 2XMMi-DR3 but the detections are still present with different SRCID values. The SRCID_2XMMi parameter can be used to find the original 2XMMi source ID for detections from the 170 sources from 2XMMi that are not in 2XMMi-DR3.

3.2.2 IAU identification

An IAU identification, IAUNAME, has been assigned to each unique source (SRCID) based upon the IAU registered classifications 2XMM and 2XMMi: a source that is included in the 2XMM catalogue has kept its 2XMM IAU identification; a source that appeared for the first time in 2XMMi retains its 2XMMi IAU identification; all new sources in 2XMMi-DR3 are also assigned an IAU name with a 2XMMi prefix.

The form of the IAU names is "2XMM Jhhmmss.sSddmmss" or "2XMMi Jhhmmss.sSddmmss" where hhmmss.s is taken from the averaged and eposcorr corrected right ascension coordinate given in the column SC_RA and Sddmmss is the averaged and eposcorr corrected declination taken from the column SC_DEC of the respective catalogue. Note that the averaged coordinates may have changed with respect to 2XMM but the IAU name with the 2XMM prefix will be the same as in the 2XMM catalogue. The situation is similar for sources in the 2XMMi catalogue where the 2XMMi prefixed IAU name is maintained.

The correct nomenclature for references to detections in the catalogue is the IAUNAME followed by a colon and the detection identification number DETID (with six digits), that is: "2XMM Jhhmmss.sSddmmss:detid" and "2XMMi Jhhmmss.sSddmmss:detid".

3.3 Updated summary html pages

Summary html pages are provided for each detection and are all newly generated, regardless of whether the detection is new or not or whether anything has changed with regard to a unique source that the detection belongs to. Where the unique source has changed, its new parameters are updated in the html page. 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 LEDAS. The slimline catalogue lists a column with the LEDAS URL which can be activated from within applications such as topcat.

3.4 Updated visual screening

The distribution of the six observation classes has slightly changed with respect to 2XMM and 2XMMi due to the continued trend of increasing occurences of 'noisy' CCDs (mainly CCD 4 of MOS1 and CCD 5 of MOS 2) in the more recent observations. Table 4 lists the observation class, the fractional area of exclusion with respect to the total detection area, and the percentage of observations affected for the 2XMMi-DR3, 2XMMi and 2XMM catalogues as well as for the new observations.

Table 4:  Distribution of observation class for the 836 new observations and for the overall observation sets used in the 2XMMi-DR3, 2XMMi and 2XMM catalogues
Obs class 'bad' area fraction    New observations    2XMMi-DR3    2XMMi    2XMM
0 0% area 26% 35% 37% 38%
1 0% < area < 0.1% 10% 12% 12% 12%
2 0.1% <= area < 1% 12% 10% 9% 10%
3 1% <= area < 10% 35% 28% 26% 25%
4 10% <= area < 100% 15% 12% 11% 10%
5 100% 3% 4% 5% 5%
Total number of observations 836 4953 4117 3491

3.5 Updated target classification

An ascii list showing the target, and, where identified, its 2XMMi-DR3 counterpart and classification, for each observation in 2XMMi-DR3, will be available shortly. A corresponding fits file will also be made available. A more detailed description of the process applied to 2XMM and 2XMMi is given in A new update, reflecting changes in the target identification procedure applied to 2XMMi-DR3, will accompany the release of the target list.

4. Catalogue content and organisation

This section summarises the organization 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 299 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 6.9 package documentation with which the bulk of the data in the 2XMMi-DR3 catalogue was processed (see 2XMM UG, App. A.3 for more details). Note that documentation for the latest public version of the SAS can be found here. 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).

Every detection in 2XMM and 2XMMi appears in 2XMMi-DR3 with the same detection identifier, DETID. New detections have DETID values of 289 084 or above. In general the 2XMM and 2XMMi unique source identifiers, SRCID, have also been preserved but there are a few cases in which this was not possible, see Sec. 3.2, but note the SRCID identifiers are not re-assigned so they are simply dropped if the source no longer exists.

Details of the columns:

Part 1: 5 columns: Identification of the source
This includes the basic static identifiers, IAU name and cross-reference to the 2XMMi source ID where relevant. 5 columns that appeared in 2XMMi relating sources there to counterparts in the 1XMM and 2XMMp catalogues were considered superfluous and are removed in 2XMMi-DR3
Part 2: 11 columns: Details of the observation and exposures
Part 3: 9 columns: Coordinates
The external equatorial and Galactic coordinates and the internal equatorial coordinates as derived from the SAS tasks eposcorr and emldetect are given together with the error estimates.
Part 4: 225 columns: Source parameters
The parameters of the source detection as derived from the SAS tasks emldetect and srcmatch are given here. Two new columns in 2XMMi-DR3 are included for the all EPIC ontime and off-axis angles
Part 5: 7 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.
Part 6: 7 columns: Source variability
This part gives variability information for those detections for which time series were extracted.
Part 7: 35 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. In addition, flags are provided to indicate where the constitution/parameters of unique sources has changed between catalogues and where confusion of sources may be present. In 2XMMi-DR3 four new columns are introduced in this section and the definition of another is modified, while two columns from 2XMMi are dropped, being replaced by the new ones.

Columns in the slimline catalogue:

Table 6 lists the 38 columns in the 2XMMi-DR3 'slimline' version of the catalogue, all of which are explained in Part 1 or Part 7 of the 2XMMi-DR3 column description, except the LEDAS_URL column which is described at the end of the table.

5. Catalogue Properties

The most important properties of the 2XMM Catalogue have been discussed in Sec. 5 of the User Guide for the 2XMM catalogue and, in more detail, in the 2XMM catalogue paper (Watson et al. 2008). An update of some basic properties of the 2XMMi catalogue were outlined in (2XMMi UG, Sec. 5). Here, we do likewise for 2XMMi-DR3.

5.1 Overview

The catalogue contains source detections drawn from 4953 XMM-Newton EPIC observations made between 2000 February 3 and 2009 October 8 and which were publicly available by 2009 October 31. Net exposure times in these observations range from < 1000 up to ~ 130000 seconds (that is, a full orbit of the satellite). Figure 5.1 shows the distribution of fields with net exposure time, Fig. 5.2 shows the distribution of fields on the sky.

The total sky area of the catalogue observations with effective exposure > 1ksec is ~ 814 deg2 which translates to ~ 504 deg2 when corrected for field overlaps. Figure 5.3 shows the sky area as a function of net exposure time (based on vignetted exposure maps, cf. 2XMM UG, Sec. 3.1.2 a)).

The catalogue contains 353191 X-ray detections with total-band (0.2 -12 keV) likelihood values ≥ 6. Of these 262902 are unique X-ray sources (Sec. 3.2), that is, 41979 X-ray sources were observed more than once and up to 38 times in total. Of the 353191 X-ray detections 30470 are classified as extended with 5770 of these being in regions considered to be 'clean'.

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 process were identified and all detections within those regions were flagged (cf. 2XMM UG, Sec. 3.2.6). Such flagged detections include spurious detections (many of which are classified as extended) as well as detections where the source parameters may be unreliable. 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. There are 246666 out of 353191 detections (70%) that have not received any flag designating a possible spurious detection or affected parameters, while 284270 out of 353191 detections (80%) can be considered to be 'clean', i.e., are unlikely to be spurious due to insufficient background determination in the source detection process (summary flag < 3). On the other hand, 2789 out of 4953 fields are considered to have no or at most a couple of spurious detections in them (observation class < 3). Note that no attempt is made to flag spurious detections arising from statistical fluctuations in the background though a preliminary analysis of the false detection rate has been made (see 2XMMi UG, Sec. 5.2 for a discussion of this).

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.

As part of the procedure to verify the integrity of the new catalogue, a number of comparisons of the 2XMMi-DR3 catalogue were made against the predecessor 2XMMi catalogue. No significant issues were identified. As an example, figure  5.5 compares the normalised distribution of the EPIC fluxes from the incremental detections in 2XMMi-DR3 against that of all the detections from 2XMMi. Plots are shown for energy bands 1 to 5. The 2XMMi-DR3 fluxes are consistent with those from 2XMMi.

5.2 False detection rates

Analysis of the false detection rates in the 2XMM and 2XMMi catalogues has been described in the 2XMMi UG, Sec. 5.2 and also applies to 2XMMi-DR3.

6. Known problems and other issues

6.1 Problem cases

6.1.1 Incorrect variability measurement

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 tentatively identified:

6.1.2 Dark columns in PN images are not represented in the exposure maps

The presence of a broad dark column in some of the PN images (and which is not represented in the exposure maps) is related to the onboard MIP rejection and to bad pixels, see the Appendix of CAL-TN-0067-0-0.pdf. As a consequence, the parameters of sources near these columns (with distance < 60 srcseconds) are underestimated.

6.1.3 PN low energy noise can cause spurious detections

Most of the PN low energy noise is suppressed by the use of PATTERN 0 events. However, in some cases bright columns or clumps of pixels appear in the images and may cause spurious detections. In most cases detections on bright columns are automatically and manually flagged (2XMM UG, Table 3.3a). As the problem has become more significant in recent years, manual flagging for new detections in 2XMMi-DR3 has also attempted to flag detections of bright clumps (which were hitherto not flagged at all). However, this process is necessarily subjective and uncertain. In most cases these sources only appear in band 1 where they could, for example, be misinterpreted as super-soft sources. As such, users are warned to treat such detections with caution, whether flagged or not.

6.1.4 Spurious sources arising from MOS low energy noise

In recent years, an increasing 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 is essentially confined to 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 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 recieve a manual flag from the visual screening process (see 2XMM UG, Sec. 3.2.6) but users should be aware of the issue.

6.2 Other issues

6.2.1 New calibrations and improved fluxes

Since early 2008, improvements in the calibration of the MOS and PN have occurred which lead to slight changes in the ECFs, particular in the soft energy bands. These, however, have not been applied in the pipeline processing of most of the observations used in making 2XMMi-DR3 (but see Sec. 6.2.2). Therefore, Table 8 gives correction factors to be applied to the ECFs and fluxes that were used in the catalogue (see 2XMM UG, Table 3.2 for the original ECFs) in the sense

improved flux = correction factor * 2XMMi-DR3 flux.

Based on these corrections, fluxes between cameras (cf. 2XMM UG, Sec. 5.3.2) are in better agreement, see for details.

Table 8: Correction factors to the ECFs and fluxes used in 2XMM and 2XMMi processing
Camera Band Open Thin Medium Thick
PN 1 1.02176 1.01139 1.00767 0.997455
2 1.02128 1.02017 1.02007 1.01950
3 0.999321 0.999288 0.999274 0.998995
4 1.01190 1.01152 1.01136 1.01107
5 1.00063 1.00000 1.00000 1.00064
9 1.01128 1.00974 1.00996 1.00902
MOS-1 1 0.981613   0.956452   0.945457   0.925115  
2 0.961381 0.961301 0.960208 0.960476
3 0.988680 0.988948 0.988765 0.989250
4 1.00000 1.00074 1.00000 1.00000
5 1.00194 1.00171 1.00170 1.00173
9 0.977969 0.978943 0.979105 0.98017
MOS-2 1 0.989302 0.959068 0.946630 0.922199
2 0.961461 0.960747 0.960899 0.959776
3 0.991415 0.991824 0.991676 0.992057
4 1.00073 1.00000 1.00075 1.00000
5 1.00300 1.00300 1.00301 1.00305
9 0.979524 0.980446 0.980451 0.981477

Note that newer canned redistribution matrices are available which, in particular, take account of the spatial affects in the MOS near the boresight. These will have a further impact on the ECFs but ECFs including these effects have not been generated for use in the pipeline processing of observations used in any of the current XMM catalogues.

6.2.2 Observations in 2XMMi-DR3 using updated ECFs

Fourteen observations in 2XMMi-DR3 are publicly available observations processed by a pipeline running since 15 April 2009 that accessed newer ECF values than used for 2XMM and 2XMMi. Table 9 identifies these 14 observations. For these cases, the correction factors shown in Table 8 do not need to be applied.

6.2.3 Mismatch between catalogue and an archived product set

One observation, OBS_ID = 0400010201 from revolution 1341, has been reprocessed again since the reprocessing in 2007 and the official, formal pipeline products from the original processing have been overwritten and are irrecoverable. These new products have also been archived in the XSA, replacing the originals. The new processing yielded 136 detections, 6 fewer than the original - this is essentially a consequence of marginally significant detections that can change due to the pixel-level spatial randomization of events during processing. To maintain consistency with 2XMMi, however, the original detection information has been used in 2XMMi-DR3. This means that the number of detections and the parameters of the detections in the 2XMMi-DR3 catalogue, for this one observation, are not consistent with the observation summary source list product currently held in the XSA.

6.2.4 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. A good example is 61Cyg whose proper motion between observations from early XMM-Newton revolutions used in 2XMM and 2XMMi and observations from more recent revolutions available in 2XMMi-DR3 is appreciable. The source is mapped to several distinct sources due to its movement (e.g. 2XMM J210654.9+384505 and 2XMMi J210656.8+384524). However, the less conservative criteria for recognizing potential confusion result in it being flagged as CONFUSED (see Sec. 3.2.1), the confusion arising from positional overlaps with other detections of itself.


Watson, M., et al. 2008, 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 28 April 2010 First release


A.1 Lists of the observations used in the catalogue and of the targets of each observation

List of observations ('fields').

List of target identifications.