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XMMSLEWCLN - XMM-Newton Slew Survey Clean Source Catalog, v1.2 |
HEASARC Archive |
The first XMM-Newton slew survey catalogue: XMMSL1.
Saxton R.D., Read A.M., Esquej P., Freyberg M.J., Altieri B., Bermejo D.
<Astron. Astrophys., 480, 611-622 (2008)>
=2008A&A...480..611S (SIMBAD/NED BibCode)
Band Energy (keV) Description
0 0.2-12 Total
4 2-12 Hard
5 0.2-2 Soft
to form three distinct surveys which have been subsequently combined to form
one catalog.
There are two related catalogs: a full catalog (the HEASARC Browse table XMMSLEWFUL constructed from the file xmmsl1D2_total.fits.gz), containing 15979 detections of sources found with a likelihood of DET_ML > 8 and a "clean" catalog (the HEASARC Browse table XMMSLEWCLN constructed from the file xmmsl1D2_clean.fits.gz) containing 7686 sources, where all known bad sources have been removed and where the detection limit has been raised to DET_ML > 10 in general and DET_ML > 14 for sources found in images with a higher than usual background. Efforts have been made to identify spurious detections and 1376 have been flagged as such in the full catalog.
There is an overlap between the slew paths, which has led to 312 sources being observed two or more times. The full catalog has an expected spurious fraction of about 20%, determined from simulations of blank fields. A cleaner subset has been created, with sources of likelihood DET_ML > 10 taken from images where the background count rate is <= 3ct/s and DET_ML > 14 for other fields. This selection is expected to contain < 1% of false sources in the soft band, ~ 9% in the hard band and ~ 4% in the total band. The number of sources (after removal of flagged sources) and the sky areas for the two catalogs are as follows:
Full catalog, sky area = 18800 deg^2:
Band Number of Sources
0 11914
4 2394
5 7841
ALL 14637
Clean catalog, sky area = 13500 deg^2 down to DET_ML > 10 and 5300 deg^2 down to DET_ML > 14:
Band Number of Sources
0 6693
4 796
5 5493
ALL 7686
The median flux is 3.0E-12 ergs/s/cm2 in the total band, 1.1E-12 in the soft band and 9.2E-12 in the hard band in the clean catalog. All sources have been cross-correlated with existing astronomical catalogs and an identification assigned for each source where found. These have been included together with the source category, e.g. Galaxy, flare star etc., as columns in the catalog together with any ROSAT All Sky Survey (RASS) counterpart. A list of IDs will be maintained. The quoted positions in the slew catalog have a 1 sigma error of 8 arcseconds which for point sources is dominated by the accuracy of the attitude reconstruction during the slewing manoeuvers. The statistical position error quoted in the catalog has a mean of ~4 arcseconds (1 image pixel) for non-extended sources. This is usually much larger for extended sources.
Detections in the three energy bands have been combined using a match radius of 30 arcseconds to identify sources detected in more than one band. The match radius is approximately 4 sigma and is reasonable for point sources because of the great scarcity of sources (0.8 detections per square degree on average) at the flux levels probed by the slew survey.
Spurious detections are produced due to systematic effects with the instruments and detection software. These sources have been screened and flagged ('T' for 'true' or 'F' for 'false') in the different categories described below. When a source is flagged true, the FLAG_COMMENT column gives a more detailed explanation of the problem for each particular source.
All sources detected in the survey have been correlated with different catalogs in order to identify the XMM-Newton slew sources with previously known objects. The catalogs used for this aim comprises two astronomical databases, a catalog of clusters of galaxies and nine other catalogs (some of them have been queried through the HEASARC astronomical database). Although the astrometric uncertainty of the slew sources was found to be 8 arcsec, the offset radius for the correlations was 30 arcsec (with a few exceptions described below) in order to include sources from catalogs with worse accuracy or truncated coordinates. For the EXOSAT CMA catalog the offset radius was 45 arcsec, and for the Einstein IPC it was 2 arcmin, both due to their high uncertainty in source coordinates. A radius of 5 arcmin was chosen for the clusters catalog due to the extension of this type of objects. As not all catalogs have the same astrometric accuracy distances are rounded to the nearest 0.1 arcmin. The identification process results in unidentified sources, sources with a single counterpart and sources with multiple matches. A hierarchical selection scheme has been applied for sources with different counterparts. A decision has been made to derive the most plausible identification candidate using the technique described below. Firstly, the SIMBAD and NED astronomical databases have been used for the cross-correlation and results from both databases have been compared in detail (SIMBAD has been queried in the frame of the Astronomical Virtual Observatory (AVO)).When a source has the same counterpart in both databases the one selected for the identification is that which gives more specification about the source category. When contradictory identification candidates have been found, the closest one has been chosen. These two databases provide the large majority (90%) of the total number of identifications. Then, a correlation with a clusters table (Abell and Zwicky Clusters of Galaxies ) has been performed. The final identification for those extended sources (ext > 2.0) with a SIMBAD/NED and also a cluster correlation comes from the clusters table. The rest of catalogs used for the cross-match are listed below ordered in priority for the preferred identification. For sources with multiple matches in a catalog, the identification was selected as the closest match. These catalogs are: All-Sky Optical Catalog of Radio/X-Ray Sources, Catalog of PSPC WGA Sources, Einstein IPC Sources Catalog, EXOSAT CMA Images/Lightcurves, ROSAT All-Sky Survey catalog, ROSAT Results Archive Sources for the PSPC, ROSAT Results Archive Sources for the HRI, RXTE Master Catalog, XMM-Newton Serendipitous Source Catalog, Version 1.1.0, INTEGRAL Bright Source Catalog. Identifications are offered for 70% of the sources.
Events are recorded initially in RAW or detector coordinates and have to be transformed, using the satellite attitude history, into sky coordinates. The tangential plane geometry commonly used to define a coordinate grid for flat images is only valid for distances of 1-2 degrees from a reference position, usually placed at the center of the image. To avoid this limitation, slew datasets were divided into roughly one square degree event files, attitude corrected and then converted into images.
Source searching used a semi-standard `eboxdetect (local) + esplinemap + eboxdetect (map) + emldetect' method, tuned to about zero background, and performed on a single image containing just the single events (pattern=0) in the 0.2-0.5 keV band, plus single and double events (pattern=0-4) in the 0.5-12.0 keV band.
The attitude information of the XMM-Newton satellite is provided by the Attitude and Orbit Control Subsystem (AOCS). A star tracker co-aligned with the telescopes allows up to a maximum of five stars to be continuously tracked giving accurate star position data every 0.5 seconds, which operates in addition to the Sun sensor that provides a precise Sun-line determination. Such information is processed resulting in an absolute accuracy of the reconstructed astrometry of typically 1 arcsecond during pointed observations. For the open-loop slews, large slews outside the star-tracker field of view of 3 x 4 degrees, the on-board software generates a three axis momentum reference profile and a two-axis (roll and pitch) Sun-sensor profile, both based on the ground slew telecommanding. During slew manoeuvring a momentum correction is superimposed onto the reference momentum profile and, as there are no absolute measurements for the yaw axis, a residual yaw attitude error exists at the end of each slew that may be corrected in the final closed-loop slew. To process slew data, attitude information is taken from a Raw Attitude File (RA F) which stores attitude points every 40-60 seconds. The times quoted in the RAF are offset from spacecraft time by 0.75 seconds, which has to be corrected in the software, otherwise a 1 arcminute offset in source positions is seen along the slew direction. Initially the correction was performed in the slew-specific software but from SAS 7.0 has been included in the general SAS software. The SAS astrometry software interpolates between the rather sparse RAF points using a curve fit. Five RAFs have been found to contain one bad attitude point which is sufficient to totally corrupt the attitude solution over a considerable section of the slew. In these cases the offending point was simply removed from the file and the resultant interpolation does not seem to degrade the astrometry significantly. In a further 7 slews a part or all of the attitude seems to be turbulent rather than smooth. It is not known why this occurs and no attempt to fix it has been made. Sources affected by this attitude problem have a position suspect (VER_PSUSP) flag set to true. The error introduced in the source positions can be of the order of 1 arcminute. A sample of point sources from the catalog with matches in the SIMBAD catalog have been analysed and show that 68% lie within 8 arcseconds of the SIMBAD position and 90% within 17 arcseconds.
XMMslew_Name
This is the official name for sources detected in the XMM-Newton slew survey.
It starts with the prefix, XMMSL1, the IAU registered designator, and then
encodes the J2000 sky position, e.g. XMMSL1 J010537.6+364858. The name is
assigned in two passes. When the three independent energy band source lists
are combined to form one catalog the source name is set using the position
in the band where the DET_ML likelihood is the highest. A second pass is then
performed such that sources which have been observed in more than one slew
are given the same name. Again, priority is given depending on the detection
likelihood. Note that the combination of XMMSLEW_NAME and observation
number (OBSID) is unique. Detections are deemed to be from the same source if
their centers lie within 30 arcseconds of each other. Note that the
statistical position error (RADEC_ERROR) calculated by the source search
software is not used in this calculation. This is because the mean error on
the slew attitude reconstruction of 8" dominates the error budget. Given the
scarcity of slew sources (0.8 per square degree) on the sky, 30" was found
to be a reasonably robust match radius for point sources. It is not so good
for extended sources and the catalog may contain multiple detections of the
same extended source with different names.
ObsID
This is the XMM-Newton observation number assigned to the slew by the
satellite scheduling system. Slew observations always begin with a 9 to
distinguish them from pointed observations, followed by a 4 digit satellite
orbit number and a 5 digit slew designator, e.g. 9031400004, refers to the
second slew of revolution 314.
Sourcenum
This is a number which uniquely identifies each detection in an observation.
RA
The Right Ascension of the source in the selected equinox. This was given in
J2000.0 coordinates and to a precision of 8 significant digits in decimal
degrees in the original table.
Dec
The Declination of the source in the selected equinox. This was given in
J2000.0 coordinates and to a precision of 8 significant digits in decimal
degrees in the original table.
RADec_Error
The statistical error of the source position, in arcseconds, as returned by
the source detection software.
LII
The Galactic Longitude of the source.
BII
The Galactic Latitude of the source.
HR1
The hardness ratio, defined as
HR1 = (COUNT_RATE_B4 - COUNT_RATE_B5) / (COUNT_RATE_B4 + COUNT_RATE_B5)
where COUNT_RATE_B4 is the hard band count rate and COUNT_RATE_B5 is the soft
band count rate. This has been calculated for all of the sources which have a
positive detection in both bands.
HR1_Error
The error in the hardness ratio, calculated as
sqrt(COUNT_RATE_B4_ERROR^2 + COUNT_RATE_B5_ERROR^2) / (COUNT_RATE_B4 +
COUNT_RATE_B5)
where COUNT_RATE_B4_ERROR and COUNT_RATE_B5_ERROR are the errors in the hard
and soft band count rates respectively.
Time
The start time of the slew containing this source.
End_Time
The end time of the slew containing this source.
Scts_B0
The number of background-subtracted counts, in the total energy band (0.2-12
keV). This number has been corrected for photons scattered outside the source
region due to the Point Spread Function (PSF).
Scts_B0_Error
The statistical 1-sigma error in the total-band source counts.
Scts_B4
The number of background-subtracted counts, in the hard energy band (2-12
keV), corrected for the PSF.
Scts_B4_Error
The statistical 1-sigma error in the hard-band source counts.
Scts_B5
The number of background-subtracted counts, in the soft energy band (0.2-2
keV), corrected for the PSF.
Scts_B5_Error
The statistical 1-sigma error in the soft-band source counts.
X_Ima_B0
The X position of the source in the total-band image in image pixels. Each
pixel covers an area of 4.1" x 4.1".
Y_Ima_B0
The Y position of the source in the total-band image in image pixels. Each
pixel covers an area of 4.1" x 4.1".
X_Ima_B4
The X position of the source in the hard-band image in image pixels. Each
pixel covers an area of 4.1" x 4.1".
Y_Ima_B4
The Y position of the source in the hard-band image in image pixels. Each
pixel covers an area of 4.1" x 4.1".
X_Ima_B5
The X position of the source in the soft-band image in image pixels. Each
pixel covers an area of 4.1" x 4.1".
Y_Ima_B5
The Y position of the source in the soft-band image in image pixels. Each
pixel covers an area of 4.1" x 4.1".
Ext_B0
The spatial extension of the source in the total energy band, in pixels. This
measures the deviation from a point source of the spatial distribution of the
source counts. It is defined as the sigma of a Gaussian which would need to
be convolved with the point spread function (PSF) to produce the observed
counts distribution. The software (emldetect) fits sources out to a maximum
extent of 20 pixels. Each pixel covers an area of 4.1" x 4.1".
Ext_B0_Error
The statistical 1-sigma error in the total-band spatial extension, in pixels.
Ext_B4
The spatial extension of the source in the hard energy band, in pixels.
Ext_B4_Error
The statistical 1-sigma error in the hard-band spatial extension, in pixels.
Ext_B5
The spatial extension of the source in the soft energy band, in pixels.
Ext_B5_Error
The statistical 1-sigma error in the soft-band spatial extension, in pixels.
Det_ML_B0
The detection likelihood in the total energy band (0.2-12 keV).
Det_ML_B4
The detection likelihood in the hard energy band (2-12 keV).
Det_ML_B5
The detection likelihood in the soft energy band (0.2-2 keV).
Ext_ML_B0
The likelihood of the source being extended in the total band.
Ext_ML_B4
The likelihood of the source being extended in the hard band.
Ext_ML_B5
The likelihood of the source being extended in the soft band.
Bg_Map_B0
The background counts per pixel for the total band.
Bg_Map_B4
The background counts per pixel for the hard band.
Bg_Map_B5
The background counts per pixel for the soft band.
Exp_Map_B0
The effective on-axis exposure time in the total energy band, in seconds.
Exp_Map_B4
The effective on-axis exposure time in the hard energy band, in seconds.
Exp_Map_B5
The effective on-axis exposure time in the soft energy band, in seconds.
Flux_B0
The source flux in the total energy band, in erg/cm^2/s.
Source fluxes have been calculated from count rates based on energy
conversion factors assuming a spectral model of an absorbed power-law
with Nh = 3.0 * 10^20 cm^-2 and a slope = 1.7. The energy conversion factors
used here are the following:
Band Conv. Factor
Total 3.159
Hard 9.144
Soft 1.436
Flux_B0_Error
The error in the total-band source flux, in erg/cm^2/s.
Flux_B4
The source flux in the hard energy band, in erg/cm^2/s.
Source fluxes have been calculated from count rates based on energy conversion factors assuming a spectral model of an absorbed power-law with Nh = 3.0 * 10^20 cm^-2 and a slope = 1.7. The energy conversion factors used here are the following:
Band Conv. Factor
Total 3.159
Hard 9.144
Soft 1.436
Flux_B4_Error
The error in the hard-band source flux, in erg/cm^2/s.
Flux_B5
The source flux in the soft energy band, in erg/cm^2/s.
Source fluxes have been calculated from count rates based on energy conversion factors assuming a spectral model of an absorbed power-law with Nh = 3.0 * 10^20 cm^-2 and a slope = 1.7. The energy conversion factors used here are the following:
Band Conv. Factor
Total 3.159
Hard 9.144
Soft 1.436
Flux_B5_Error
The error in the soft-band source flux, in erg/cm^2/s.
Count_Rate_B0
The total band count rate, in counts/second.
Count_Rate_B0_Error
The error in the total band count rate.
Count_Rate_B4
The hard band count rate, in counts/second.
Count_Rate_B4_Error
The error in the hard band count rate.
Count_Rate_B5
The soft band count rate, in counts/second.
Count_Rate_B5_Error
The error in the soft band count rate.
RA_B0
The J2000 Right Ascension of the total-band source, in degrees.
Dec_B0
The J2000 Declination of the total-band source, in degrees.
RADec_B0_Error
The statistical 1-sigma error in the total-band source
position, in arcseconds.
LII_B0
The Galactic Longitude of the total-band source, in degrees.
BII_B0
The Galactic Latitude of the total-band source, in degrees.
RA_B4
The J2000 Right Ascension of the hard-band source, in degrees.
Dec_B4
The J2000 Declination of the hard-band source, in degrees.
RADec_B4_Error
The statistical 1-sigma error in the hard-band source
position, in arcseconds.
LII_B4
The Galactic Longitude of the hard-band source, in degrees.
BII_B4
The Galactic Latitude of the hard-band source, in degrees.
RA_B5
The J2000 Right Ascension of the soft-band source, in degrees.
Dec_B5
The J2000 Declination of the soft-band source, in degrees.
RADec_B5_Error
The statistical 1-sigma error in the soft-band source
position, in arcseconds.
LII_B5
The Galactic Longitude of the soft-band source, in degrees.
BII_B5
The Galactic Latitude of the soft-band source, in degrees.
Val_Flag
This flag indicates the source is included in the clean sample.
Srcname_B0
The source name defined in the total-band list. The format
is 'xs' followed by the revolution number, the observation ID and the
source position, e.g., 'xs0841_9084100002_12:57:07.5+01:50:42'.
Srcname_B4
The source name defined in the hard-band list. The format
is 'xs' followed by the revolution number, the observation ID and the
source position, e.g., 'xs0841_9084100002_12:57:07.5+01:50:42'.
Srcname_B5
The source name defined in the soft-band list. The format
is 'xs' followed by the revolution number, the observation ID and the
source position, e.g., 'xs0841_9084100002_12:57:07.5+01:50:42'.
Ximname_B0
The name of the image containing the total-band detection.
Ximname_B4
The name of the image containing the hard-band detection.
Ximname_B5
The name of the image containing the soft-band detection.
Ver_Inext
If set to 'T' (true), this flag notes that a detection has been
found within an extended source and is probably spurious. This flag is used
to ensure that only one source is quoted for the large supernova remnants.
Ver_Halo
If set to 'T' (true), this flag indicates that a detection lies
within the point spread function, or halo, of a very bright source, and is
probably spurious.
Ver_Hibgnd
If set to 'T' (true), this flag indicates that the source lies
within a bright region, caused by high background, and is probably spurious.
Ver_Nredg
If set to 'T' (true), this flag indicates that the source has
been detected in two consecutive images of the same slew. This can occur if
the source lies on the border between slews and implies that the position of
the source is unlikely to be accurate.
Ver_Psusp
This flag indicates that the quoted position of the source is
likely to be inaccurate. In a few slews, the attitude reconstruction is poor
and, in these cases, the actual position of the source is difficult to
determine, and can be wrong by an arcminute.
Ver_False
This is a catch-all for problems not included in the other flags.
In the catalog, only two sources have this flag set true; in both cases, it is
because the exposure time has been calculated as zero for reasons which
remain unclear.
Flag_Comment
A comment which explains why a particular source flag has been
set to true.
Name
Cross-correlations of the positions of the slew sources with
astronomical databases and catalogs have been performed.
This parameter gives the catalog name of the best match.
Alt_Name
An alternative designation for the best-matched source.
RASS_Name
The name of the closest ROSAT All-Sky Survey (RASS) source to
the position of the XMM-Newton Slew source.
ID_Category
The source type, as determined by SIMBAD, NED, and the other
resources used in the cross-matching process. This is directly taken from the
catalog in question, and no attempt has been made to rationalize the values.
ID_Resource
The astronomical database or catalog from which the best match
has been selected, e.g., SIMBAD, NED, etc.
ID_Offset
The angular distance in arcminutes between the best match candidate and the
XMM-Newton Slew Survey source. The resolution is set at 0.1 arcmins because
this is the resolution in which the values are available from NED, and also
because the best match candidate often has a large error in its position.
RASS_Offset
The angular distance between the best matching ROSAT source and the XMM-Newton
Slew Survey source, in arcseconds.
Mode_ID
The observing mode of the EPIC-pn camera, where 'FF' means
full-frame mode, 'eFF' extended full-frame mode, and 'LW' means large window
mode.
Image_Bg_Rate
The peak background count rate in the image from which the source was
extracted, in counts/second. This is measured as the count rate, over the
whole image, for events with energy > 10 keV (PI > 10000). It is quoted to a
resolution of 0.1 ct/s and is used to determine the overall background
environment in which a source was detected. This value is used in the
creation of a clean subsample of the catalog (see Description above).
Generally, the higher this value, the greater the probability that the source
is spurious. This is especially true if the detection likelihood of the
source is less than 14. The value has been tabulated for images with a
background rate greater than 2 ct/s. For quieter images the value has been
artifically set to 1.9 ct/s.
Class
The HEASARC Browse object classification, based on the value of the
ID_CATEGORY parameter.