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Last modified: 21 March 2017

URL: http://cxc.harvard.edu/csc/preliminary/index.html

Chandra Source Catalog Release 2.0 Preliminary Detections List

[NOTE]
Note

This is a work in progress! Be sure to read the caveats prior to using these data! The Spring 2016 CXC Newsletter article provides more information on the state of version 2 of the Chandra Source Catalog .

Contents


Data Access

The March 2017 release of the data is available at:

It contains the results of Maximum Likelihood Estimator (MLE) fits to the candidate source detections. The column definitions and Caveats for this file can be found below. The file contains 362182 detections, with 279549 labelled as SRC_QUALITY = ‘TRUE’ and 82633 (23%) with SRC_QUALITY = ‘MARGINAL’. When split by EXTSRC_CLASS, there are 358382 detections with a value of ‘POINT’, 3183 (0.9%) with ‘EXTENDED’, and 617 (0.2%) with ‘POSSIBLE’. The breakdown by EBAND—the energy band correponding to the measured values—there are 271687 broad band ('b'), 395 ultra-soft ('u'), 26995 soft ('s'), 26524 medium ('m'), 31297 hard ('h'), and 5284 wide (HRC) band ('w') rows; the band definitions are the same as in release 1. There are 354 detections with STREAK_SRC_FLAG = True.

Column Definitions

unix% dmlist preliminary_detlist.fits blocks
 
--------------------------------------------------------------------------------
Dataset: preliminary_detlist.fits
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     Block Name                          Type         Dimensions
--------------------------------------------------------------------------------
Block    1:                                Null        
Block    2: DETLIST                        Table        48 cols x 362182   rows

DETLIST HDU: PRELIMINARY DETECTIONS LIST

Column name Units Comment Example Data type FITS format Notes
DETECT_ID Stack_id.component 'acisfJ0123456p012345_001.0001' string 29A
LIKELIHOOD Highest source log likelihood 100.0 double 1D Highest source likelihood
SRC_QUALITY Preliminary source quality 'TRUE' string 8A Values are 'TRUE' or 'MARGINAL' and are based on comparison of likelihood with draft catalog thresholds.
EBAND Energy band of maximum likelihood value 'b' string 1A Energy band corresponding to likelihood value; Science energy band designation (i.e., lower case) not detect energy band: one of 'b', 'u', 's', 'm', 'h', or 'w'.
THETA arcmin Highest likelihood src model mean off-axis ang 0.0 double 1D Corresponds to fitted [x,y]
STREAK_SRC_FLAG Is source on a streak? 'F' logical 1L
RA deg Highest likelihood source model position RA 20.94000 double 1D
DEC deg Highest likelihood source model position Dec 1.39583 double 1D
ERR_ELLIPSE_RA deg 95% confidence error ellipse position RA 20.94000 double 1D 95% confidence error ellipse RA in deg; 0.0 <= ERR_ELLIPSE_RA < 360.0
ERR_ELLIPSE_DEC deg 95% confidence error ellipse position Dec 1.39583 double 1D 95% confidence error ellipse Dec in deg; -90.0 <= SRC_ERR_ELLIPSE_DEC_B <= +90.0
ERR_ELLIPSE_R0 arcsec 95% confidence error ellipse semi-major axis 0.35 double 1D 95% confidence error ellipse semi-major axis radius in arcsec
ERR_ELLIPSE_R1 arcsec 95% confidence error ellipse semi-minor axis 0.30 double 1D 95% confidence error ellipse semi-minor axis radius in arcsec
ERR_ELLIPSE_ANG deg 95% confidence error ellipse smaj axis rotang 60.0 double 1D 95% confidence error ellipse rotation angle of semi-major axis; 0.0 <= ERR_ELLIPSE_ANG < 180.0; 0.0 along SKY +X, 90.0 along SKY +Y
SRC_RDATA_B count Raw data counts in ECF90 aperture ACIS b band 100 long 1J
SRC_AMPL_B photon/cm**2/s Best fit point src model amplitude ACIS b band 1.00E-08 double 1D
SRC_AMPL_LOLIM_B photon/cm**2/s 68% confidence lower limit on SRC_AMPL_B 9.00E-09 double 1D
SRC_AMPL_HILIM_B photon/cm**2/s 68% confidence upper limit on SRC_AMPL_B 1.10E-08 double 1D
SRC_RDATA_S count Raw data counts in ECF90 aperture ACIS s band 30 long 1J
SRC_AMPL_S photon/cm**2/s Best fit point src model amplitude ACIS s band 3.00E-09 double 1D
SRC_AMPL_LOLIM_S photon/cm**2/s 68% confidence lower limit on SRC_AMPL_S 2.00E-09 double 1D
SRC_AMPL_HILIM_S photon/cm**2/s 68% confidence upper limit on SRC_AMPL_S 4.00E-09 double 1D
SRC_RDATA_M count Raw data counts in ECF90 aperture ACIS m band 50 long 1J
SRC_AMPL_M photon/cm**2/s Best fit point src model amplitude ACIS m band 5.00E-09 double 1D
SRC_AMPL_LOLIM_M photon/cm**2/s 68% confidence lower limit on SRC_AMPL_M 4.00E-10 double 1D
SRC_AMPL_HILIM_M photon/cm**2/s 68% confidence upper limit on SRC_AMPL_M 6.00E-09 double 1D
SRC_RDATA_H count Raw data counts in ECF90 aperture ACIS h band 20 long 1J
SRC_AMPL_H photon/cm**2/s Best fit point src model amplitude ACIS h band 2.00E-09 double 1D
SRC_AMPL_LOLIM_H photon/cm**2/s 68% confidence lower limit on SRC_AMPL_H 1.00E-09 double 1D
SRC_AMPL_HILIM_H photon/cm**2/s 68% confidence upper limit on SRC_AMPL_H 3.00E-09 double 1D
SRC_RDATA_W count Raw data counts in ECF90 aperture HRC w band TNULL long 1J
SRC_AMPL_W photon/cm**2/s Best fit point src model amplitude HRC w band NaN double 1D
SRC_AMPL_LOLIM_W photon/cm**2/s 68% confidence lower limit on SRC_AMPL_W NaN double 1D
SRC_AMPL_HILIM_W photon/cm**2/s 68% confidence upper limit on SRC_AMPL_W NaN double 1D
EBAND_EXT Energy band of extended source model properties 's' string 1A Energy band corresponding to reported extended source parameters: set to ' ' if not evaluated, otherwise one of 'b', 'u', 's', 'm', 'h', or 'w'.
EXTSRC_CLASS Extended source classification 'POSSIBLE' string 8A 'POINT', 'EXTENDED', or 'POSSIBLE'
EXT_RDATA count Raw data counts in source region aperture 40 long 1J
EXT_AMPL photon/cm**2/s Best fit ext src model amplitude 2.50E-09 double 1D
EXT_AMPL_LOLIM photon/cm**2/s 68% confidence lower limit on EXT_AMPL 1.50E-09 double 1D
EXT_AMPL_HILIM photon/cm**2/s 68% confidence upper limit on EXT_AMPL 3.50E-09 double 1D
EXT_SMAJ arcsec Best fit extended source model semi-major axis 5.0 double 1D
EXT_SMIN arcsec Best fit extended source model semi-minor axis 3.5 double 1D
EXT_ROTANG deg Best fit extended source model rotation angle 30.0 double 1D
EXT_SMAJ_LOLIM arcsec 68% confidence lower limit on EXT_SMAJ 4.5 double 1D
EXT_SMAJ_HILIM arcsec 68% confidence upper limit on EXT_SMAJ 5.5 double 1D
EXT_SMIN_LOLIM arcsec 68% confidence lower limit on EXT_SMIN 3.0 double 1D
EXT_SMIN_HILIM arcsec 68% confidence upper limit on EXT_SMIN 4.0 double 1D
EXT_ROTANG_LOLIM deg 68% confidence lower limit on EXT_ROTANG 10.0 double 1D
EXT_ROTANG_HILIM deg 68% confidence upper limit on EXT_ROTANG 50.0 double 1D

Caveats

  1. This version of the preliminary detections table is constructed from a partial run of Chandra observations that will be included in release 2.0 of the CSC, and includes 362,182 detections from 7,247 observation stacks.

  2. Roughly 0.5% of observation stacks have not yet completed processing or are awaiting manual quality assurance review. The list of observation stacks not included in this version of the preliminary detections table is reported in Table 1.

  3. The preliminary detections table includes detections and not sources. In particular:

    • Sources that are detected in multiple observation stacks are not combined in any way. Each detection is reported separately.

    • Off-axis detections from one observation stack may correspond to multiple detections in another observation stack where the detections are on-axis. These matches will be resolved in second major catalog processing phase.

    • As a consequence, source names have not yet been assigned. Instead, an identifier has been provided for each detection. Note that the identifiers included in this version of the preliminary detections table may not match the identifiers included in the August 2015 version of the table because a significant fraction of the observation stacks required complete reprocessing since then.

  4. Detections:

    • A small number of compact detections identified as definitely or possibly extended (extsrc_class = ‘EXTENDED’ or ‘POSSIBLE’) may consist of a close association (typically a pair or triple) of point detections. These will not be corrected in the final catalog.

    • Detections that are extremely piled-up (cratered) have likelihood = +Inf. A very small number (of order 10) of these detections are incorrectly classified and will be corrected in the final catalog.

  5. Positions and position errors:

    • Position errors are typically reported in the form of an error ellipse that records the statistical confidence limits derived from a Markov chain Monte Carlo (MCMC) analysis of the fitted source model. The ellipse angle in the preliminary detections table defines 0° along the +X axis (i.e., the same definition as used by the DS9 imager); however, true astronomical position angles (measured from North through East) will be used in the final catalog.

    • If the MCMC analysis did not converge (typically due to low S/N) then a circularly symmetric estimate of the position errors is provided.

    • Reported position errors do not include the absolute uncertainty in the astrometry relative to the reference frame. The systematic error derived from release 1 of the catalog (0.16″ radial) should be a reasonable estimate of this value, and this number should be added in quadrature to the report position errors to get the best estimate of the absolute position uncertainty on the sky.

  6. Aperture photometry:

    • Fit amplitudes are provided as proxies for the full Bayesian aperture photometry analysis that will be included in the final catalog (see Figure 1). While these are expected to be reasonably reliable for relative photometry on a statistical basis, systematic uncertainties for a single detection basis may be large. Detailed Bayesian X-ray aperture photometry for each source will be calculated as part of the second major catalog processing phase.

  7. Miscellaneous notes:

    • The detections have undergone all standard quality assurance reviews, and except for the caveats noted herein should match those that will be included in the final catalog.

    • Detections identified near the edges of (stacked observation) fields, near edges of individual observations within observation stacks, near areas of extended emission, and on readout streaks, may have a higher than nominal false detection rate. If this is a concern, we recommend that users review images of the individual observations from the Chandra Data Archive.

    • Detections are categorized as ‘MARGINAL’ or ‘TRUE’ (recorded under src_quality) depending on their likelihood. These categorizations are those that will appear in the final catalog.

    • Detections near the edges of the field of each observation, or near the gap between adjacent back-illuminated and front-illuminated ACIS-S CCDs, or on bright ACIS readout streaks, are not included. This is intentional because these detector areas had an excessively high false source rate in release 1 of the catalog. In the final catalog release, the detection sensitivity will be set to zero in these areas. However, detection sensitivity information will not be available until completion of the second major catalog processing phase.

    • Only point and compact detections are included. Extended (“convex hull”) detections are not included in the preliminary detections table, but will appear in the final catalog release.

Table 1:
List of Observation Stacks not included in the current version of the Preliminary Detections Table.
acisfJ0011407m152147_001 acisfJ0319443p413138_001 acisfJ0534316p220052_001
acisfJ0534322p215837_001 acisfJ0534340p221143_001 acisfJ0535165m052323_001
acisfJ0538411m690602_001 acisfJ0955442p694142_001 acisfJ1047086m600555_001
acisfJ1047429p135930_001 acisfJ1048174p123757_001 acisfJ1115042m611530_001
acisfJ1124354m591559_001 acisfJ1214458m652812_001 acisfJ1230487p122327_001
acisfJ1325492m425819_001 acisfJ1325538m425945_001 acisfJ1330038p471057_001
acisfJ1424365p225555_001 acisfJ1501079p014443_001 acisfJ1513347m590144_001
acisfJ1513347m590144_001 acisfJ1523045p083741_001 acisfJ1611413m014634_001
acisfJ1712268m232325_001 acisfJ1713442m370615_001 acisfJ1721036m372619_001
acisfJ1745401m290028_001 acisfJ1748454m271007_001 acisfJ1800276m240230_001
acisfJ1846224m025742_001 acisfJ1907327p070619_001 acisfJ2208400p454446_001
acisfJ2239250m054359_001 acisfJ2308192m020958_001 acisfJ2323333p584655_001
acisfJ2323335p585100_001 acisfJ2323390p585033_001 acisfJ2343503m151712_001
hrcfJ0044069p414315_001
[Thumbnail image: There is a strong linear correlation between the Bayesian photometry value (X axis) and the fitted source amplitude (Y axis), with the scatter being lower for the TRUE sources compared to the MARGINAL ones.]

[Version: full-size, PDF]

[Print media version: There is a strong linear correlation between the Bayesian photometry value (X axis) and the fitted source amplitude (Y axis), with the scatter being lower for the TRUE sources compared to the MARGINAL ones.]

Comparison of source photometry

Correlation between the fitted source amplitude and detailed Bayesian X-ray aperture photometry analysis for 14,360 detections, in the ACIS broad energy band. Note that the correlation is somewhat worse for faint detections categorized as ‘MARGINAL’. The correlation has not been demonstrated for energy bands other than the ACIS broad band; however, we expect that the correlations in the other bands should be similar.


Last modified: 21 March 2017
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