Source parameters (225 columns)

In the following each parameter is described in general together with the error (where applicable). A table then indicates the combinations of camera (ca = EP, PN, M1, M2) and bands (b = 1, 2, 3, 4, 5, 8, 9; see 2XMM UG Tab. 3.1). 'EP' stands for EPIC and indicates parameters combined from those from the available cameras. Most parameters are determined by the SAS task emldetect, which does a simultaneous maximum likelihood PSF fit to the source count distribution in each energy band and camera (for details see 2XMM UG Sec. 3.1.2 f))

XID values (band 9) are derived in a seperate run of emldetect on input images, exposure maps and background maps that are merged for the bands 2, 3, 4. The input source position were taken from the first run (which determined the bands 1 - 5 and band 8 values) and kept fixed. As a consequence XID values are single-band values, which ensures a better handling of the error values, cf. 2XMM UG Sec. 3.1.2 g).

Entries have a NULL when the detection was not observed with the respective camera.

The individual parameters are (ca = EP, PN, M1, M2; b = 1, 2, 3, 4, 5, 8, 9; n = 1, 2, 3, 4):

Fluxes: ca_b_FLUX and ca_b_FLUX_ERR
Count rates: ca_b_RATE and ca_b_RATE_ERR
Source counts: ca_b_CTS and ca_b_CTS_ERR
Maximum likelihoods: ca_b_DET_ML
Extent parameters: EP_EXTENT, EP_EXTENT_ERR, and EP_EXTENT_ML
Hardness ratios: ca_HRn and ca_HRn_ERR
Exposure map: ca_b_EXP
Background map: ca_b_BG
Vignetting: ca_b_VIG
Ontime values: ca_ONTIME
Offaxis angle: ca_OFFAX
Maskfrac value: ca_MASKFRAC
Distance to the nearest neighbour: DIST_NN


Fluxes

Fluxes are given in erg/cm2/s and are calculated by the SAS tasks emldetect and by srcmatch for the input bands (see Secs 3.1.2 f) and  i)). Note that they correspond to the flux in the entire PSF and do not need any further corrections for PSF losses.

For the individual cameras, individual-band fluxes (bands 1 - 5, 9) are calculated from the respective band count rate using the filter- and camera-dependent energy conversion factors given in Tab. 3.2 and corrected for the dead time due to the read-out phase. These can be 0.0 if the detection has no counts. The respective errors are calculated from the respective band count rate error using the respective energy conversion factors.

Combined band fluxes (band 8) for the individual cameras are the sum of the fluxes and errors from each band (1 - 5).

The EPIC flux in each band is the mean of the band-specific detections in all cameras weighted by the errors, with the error on the weighted mean given by
EP_b_FLUX_ERR = SQRT (  1.0 / SUM ( 1 / ca_b_FLUX_ERR2 )), where ca = PN, M1, M2.

Columns ca_b_FLUX and ca_b_FLUX_ERR:   (E)   [erg/cm**2/s]SAS tasks emldetect, srcmatch

ca \ b 8 1 2 3 4 5 9
EP flux [err]  flux [err]  flux [err]  flux [err]  flux [err]  flux [err]  flux [err] 
PN flux [err]  flux [err]  flux [err]  flux [err]  flux [err]  flux [err]  flux [err] 
M1 flux [err]  flux [err]  flux [err]  flux [err]  flux [err]  flux [err]  flux [err] 
M2 flux [err]  flux [err]  flux [err]  flux [err]  flux [err]  flux [err]  flux [err] 


Note that an error that affected around 17-20% of the EPIC (EP) band 4 fluxes in the previous 2XMMp, 2XMM and 2XMMi catalogues is fixed in the 2XMMi-DR3 catalogue (see here for more details).

Count Rates

Count rates and errors are given in counts per second and are derived by the SAS task emldetect (see Sec. 3.1.2 f)).

The individual-band count rate (bands 1 - 5, 9) is the band-dependent source counts (ca_b_CTS) divided by the exposure map, which combines the mirror vignetting, detector efficiency, bad pixels and CCD gaps (cf. SSC-LUX-SP-0004.ps, Sec. 6.5.2.6), and an OOT-factor (Out Of Time), depending on the PN modes (PN_SUBMODE). The source counts and with it the count rates were implicitly background subtracted during the fitting process. They correspond to the count rate in the entire PSF and do not need any further corrections for PSF losses. Note that rates can be 0.0 (but not negative) if the source is too faint in the respective band to be detectable.

Combined band count rate (band 8) for each camera are calculated as the sum of the count rates in the individual bands 1 - 5.

The EPIC rates are the sum of the camera-specific count rates in the respective band.

Columns ca_b_RATE and ca_b_RATE_ERR:   (E)   [count/s]SAS task emldetect

ca \ b 8 1 2 3 4 5 9
EP rate [err]  - - - - - rate [err] 
PN rate [err]  rate [err]  rate [err]  rate [err]  rate [err]  rate [err]  rate [err] 
M1 rate [err]  rate [err]  rate [err]  rate [err]  rate [err]  rate [err]  rate [err] 
M2 rate [err]  rate [err]  rate [err]  rate [err]  rate [err]  rate [err]  rate [err] 


Source Counts

Source counts and errors are given in counts and are derived by the SAS task emldetect (see Sec. 3.1.2 f)).

The individual-band source counts (not given in the catalogue) are derived under the total PSF (point spread function) and corrected for background. The PSF is fitted on subimages of radius 60 arcseconds in each band (CUTRAD), which means, that in most cases at least 90 % of the PSF (if covered by the detector) was effectively used in the fit.

Combined band source counts (band 8) for each camera are calculated as the sum of the source counts in the individual bands 1 - 5.

The EPIC band 8 counts are the sum of the (available) individual camera band 8 counts

The error is the statistical 1 σ error on the total source counts of the detection.

Columns ca_b_CTS and ca_b_CTS_ERR:   (E)   [count]SAS task emldetect

ca \ b 8 1 2 3 4 5 9
EP cts [err]  - - - - - -
PN cts [err]  - - - - - -
M1 cts [err]  - - - - - -
M2 cts [err]  - - - - - -


Maximum Likelihoods

Maximum likelihoods are derived by the SAS task emldetect (see Sec. 3.1.2 f)).

The individual-band maximum likelihood values (bands 1 - 5, 9) stand for the detection likelihood of the source, L = - ln p, where p is the probability of the detection occurring by chance. While the detection likelihood of an extended source is computed in the same way, systematic effects such as deviations between the real background and the model, have a larger effect on extended sources and thus detection likelihoods of extended sources are more uncertain.

To calculate the maximum likelihood values for the combined band 8 and EPIC the sum of the individual likelihoods is being normalised to two degrees of freedom using the function

ML_corr = gammaq (ndof/2, ML),

where

ndof = 2 (for xpos,ypos) + N_images for point sources,
ndof = 3 (for xpos,ypos,extent) + N_images for extended sources,
gammaq = - ln (Q(a,x)) = - ln (1 - P(a,x)),
and P is the incomplete gamma function.

Columns ca_b_DET_ML:   (E)SAS task emldetect

ca \ b 8 1 2 3 4 5 9
EP detml  - - - - - detml 
PN detml  detml  detml  detml  detml  detml  detml 
M1 detml  detml  detml  detml  detml  detml  detml 
M2 detml  detml  detml  detml  detml  detml  detml 


Extent Parameters

The extent radius and error as well as the extent likelihood of a source detected as extended is determined by the SAS task emldetect (see Sec. 3.1.2 f)). It is determined fitting a beta-model profile to the source PSF. Anything below 6" is considered to be a point source and the extent is set to zero. To avoid non-converging fitting an upper limit of 80" has been introduced.

Columns EP_EXTENT and EP_EXTENT_ERR:   (E)  [arcsec]SAS task emldetect

ca \ b 8 1 2 3 4 5 9
EP ext [err]  - - - - - -
PN - - - - - - -
M1 - - - - - - -
M2 - - - - - - -

The extent likelihood is the likelihood of the detection being extended as given by EXTENT_ML = - ln (P) , where P is the probability of the extent occurring by chance.

Column EP_EXTENT_ML   (E)SAS task emldetect

ca \ b 8 1 2 3 4 5 9
EP extent ml  - - - - - -
PN - - - - - - -
M1 - - - - - - -
M2 - - - - - - -


Hardness Ratios

The hardness ratios for each camera are derived by the SAS task emldetect (see Sec. 3.1.2 f)). They are defined as the ratio between the bands A and B:

HR(A,B) = (band B - band A) / (band A + band B).

Note that in the case where the rate in one band is 0.0 (i.e., too faint to be detected in this band) the hardness ratio will be -1 or +1 which is only a lower or upper limit, respectively. In case where the rate in both bands is zero, the hardness ratio is undefined (NULL).

There are four hardness ratios (n) using the following bands:

HR1: bands 1 & 2
HR2: bands 2 & 3
HR3: bands 3 & 4
HR4: bands 4 & 5

Errors are the 1 σ error on the hardness ratio 1 as derived by the SAS task emldetect.

EPIC hardness ratios are calculated by the SAS task srcmatch and are averaged over all three cameras (PN, M1, M2). Note that no energy conversion factor was used and that the EPIC hardness ratios are de facto not hardness ratios but an equivalent number helpful to characterise the hardness of a source.

Columns ca_HRn and ca_HRn_ERR:   (E)SAS tasks emldetect, srcmatch

ca \ n 1 2 3 4
EP hr [err]  hr [err]  hr [err]  hr [err] 
PN hr [err]  hr [err]  hr [err]  hr [err] 
M1 hr [err]  hr [err]  hr [err]  hr [err] 
M2 hr [err]  hr [err]  hr [err]  hr [err] 


Exposure Maps

The exposure maps are made by the SAS task eexpmap (see Sec. 3.1.2 a)); they combine the mirror vignetting, detector efficiency, bad pixels and CCD gaps, cf. SSC-LUX-SP-0004.ps, Sec. 6.5.2.6. The exposure map values in the catalogue are given in seconds and are derived by the SAS task emldetect as the PSF weighted mean of the area of the subimages (radius 60 arcseconds) in the individual-band exposure maps.

Columns ca_b_EXP:   (E)  [s]SAS task emldetect

ca \ b 8 1 2 3 4 5 9
EP - - - - - - -
PN - exp  exp  exp  exp  exp  -
M1 - exp  exp  exp  exp  exp  -
M2 - exp  exp  exp  exp  exp  -


Background Maps

The background maps are made by the SAS task esplinemap (see Sec. 3.1.2 d)); they are made using a 12 x 12 nodes spline fit on the source-free individual-band images. The background map values in the catalogue are given in counts per pixel and are derived by the SAS task emldetect as the background map value at the given detection position. Note that the source fitting routine uses the background map itself rather than the single value given here. The value is zero if the detection position lies outside the FOV.

Columns ca_b_BG:   (E)  [count/pixel]SAS task emldetect

ca \ b 8 1 2 3 4 5 9
EP - - - - - - -
PN - bg  bg  bg  bg  bg  -
M1 - bg  bg  bg  bg  bg  -
M2 - bg  bg  bg  bg  bg  -


Vignetting

The vignetting values in the catalogue are derived by the SAS task emldetect (see Sec. 3.1.2 f)); they are a function of energy band and offaxis angle. (Vignetting values used in the source parametrization come from the vignetted exposure maps.)

Columns ca_b_VIG:   (E)SAS task emldetect

ca \ b 8 1 2 3 4 5 9
EP - - - - - - -
PN - vig  vig  vig  vig  vig  -
M1 - vig  vig  vig  vig  vig  -
M2 - vig  vig  vig  vig  vig  -


Ontime Values

The ontime value, given in seconds, is the total good exposure time (after GTI filtering) of the CCD where the detection is positioned. Note that some source positions fall into CCD gaps or outside of the detector and will have therefore a NULL given. A new column is introduced in 2XMMi-DR3 for the all EPIC (EP) value and represents the largest ontime value of any of the individual cameras used

Columns ca_ONTIME:   (E)  [s]

ca \ b 8 1 2 3 4 5 9
EP ontime  - - - - - -
PN ontime  - - - - - -
M1 ontime  - - - - - -
M2 ontime  - - - - - -


Offaxis Angle

The offaxis angle, given in arcminutes, is the distance between the detection position and the onaxis position on the respective detector. Note that the offaxis angle for a camera can be larger than 15 arcminutes when the detection is located outside the FOV of that camera. A new column is included in 2XMMi-DR3 for the all EPIC (EP) value which is the smallest of the individual camera values.

Columns ca_OFFAX:   (E)  [arcmin]SAS task emldetect

ca \ b 8 1 2 3 4 5 9
EP offax  - - - - - -
PN offax  - - - - - -
M1 offax  - - - - - -
M2 offax  - - - - - -


Maskfrac Value

The maskfrac value is the PSF weighted mean of the detector coverage of a detection as derived from the detection mask (see Sec. 3.1.2 b) for details). It depends slightly on energy; only band 8 values are given here which are the minimum of the energy-dependent maskfrac values. Sources which have less than 0.15 of their PSF covered by the detector are considered as being not detected.

Columns ca_MASKFRAC:   (E)SAS task emldetect

ca \ b 8 1 2 3 4 5 9
EP - - - - - - -
PN maskfrac  - - - - - -
M1 maskfrac  - - - - - -
M2 maskfrac  - - - - - -


Distance to the Nearest Neighbour

The distance to the nearest neighbouring detection is given in arseconds; they are derived by the SAS task emldetect (see Sec. 3.1.2 f)). Emldetect uses an internal threshold of 6 arseconds (before positional fitting) for splitting a source into two.

Columns ca_DIST_NN:   (E)  [arcsec]SAS task emldetect

ca \ b 8 1 2 3 4 5 9
EP distnn  - - - - - -
PN - - - - - - -
M1 - - - - - - -
M2 - - - - - - -