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Last modified: 20 September 2019


Catalog Processing

The CSC is created by processing each Chandra dataset with a series of automated data analysis pipelines. Collectively, the pipelines are known as "Level 3 Processing" and the data products reflect that in their filenames—e.g. the event file suffix is evt3.fits. For more on this nomenclature, see Chandra Standard Data Processing, which also describes the Level 1 and 2 Chandra data products.

The pipelines run in order:
Observation Selection » Pre-Calibrate/Pre-Detect Pipeline » Fine Astrometry Pipeline » Calibrate Pipeline » ComboDet Pipeline » Source Validation Pipeline » MLE Pipeline » Rebundle » MLE Pipeline run 2 » Stacker Pipeline » Master Match Pipeline » Source Properties Pipeline

Observation Selection

The Observation Selection page describes which observation intervals (OBIs) are chosen for catalog processing.

Each observation interval is assigned to a 'stack' such that all coaligned (within 1 arcmin) observations are in the same stack and can therefore be processed as a group. Stacks may therefore contain one or more observation intervals.

Pre-Calibrate/Pre-Detect Pipeline

The Pre-Calibrate pipeline is run for each OBI that's a member of a stack with more than one OBI.

The Pre-Detect step uses a run of the wavdetect program with conservative parameter settings to identify bright point sources suitable for astrometrically matching the observations that comprise each observation stack.

Fine Astrometry Pipeline

The Fine Astrometry pipeline runs to compute the astrometric corrections needed to align each observation in a stack to the same astrometric frame. It is run on the observations that went through the Pre-Calibrate/Pre-Detect pipeline.

Calibrate Pipeline

The Calibrate pipeline is run for each OBI chosen by the observation selection process.

ComboDet Pipeline

The ComboDet (combine and detect) pipeline is run for each calibrated OBI from the Calibrate pipeline to create combined data products and identify candidate source detections.

Source Validation Pipeline

The Source Validation pipeline is run to reconcile the source lists.

MLE Pipeline Run 1

The MLE (Maximum Likelihood Estimator) pipeline takes the candidate sources in each bundle and assesses them using a source region sigificantly larger than the PSF, updating the source positions and evaluating their likelihood values.


The Rebundle step checks the new source positions and recalculates the assignment of sources to bundles.

MLE Pipeline Run 2 (Recenter)

The MLE (Maximum Likelihood Estimator) pipeline takes the candidate sources in each reassigned bundle and assesses them, using smaller source regions. The source positions are further updated. The steps are the same as for the first run.

After the run, QA is performed to inspect and adjust bundle positions where needed.

Stacker Pipeline

The Stacker pipeline creates a merged detection list for an observation stack.

Master Match Pipeline

The Master Match pipeline reconciles detections of the same source in different stacks. The method is similar to that used in Release 1.

Source Properties Pipeline

The Source Properties pipeline is run for each master source and energy band.

Convex Hull Pipeline

The convex hull pipeline will be run for each band and ensemble to complete the analysis of highly extended sources. It is still under development.

Limiting Sensitivity Pipeline

The limiting sensitivity pipeline will calculate the sensitivity in each band for each location covered by the catalog. This will be provided to the community as a separate data product. The pipeline is under development.