Chandra Source Catalog Release 2.0 Preliminary Detections List
The March 2017 release of the data is available at:
- preliminary_detlist.fits.gz (53.4 Mb compressed and 124.4 Mb uncompressed)
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.
unix% dmlist preliminary_detlist.fits blocks -------------------------------------------------------------------------------- Dataset: preliminary_detlist.fits -------------------------------------------------------------------------------- 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|
|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|
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.
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.
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.
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.
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.
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.
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.