Last modified: 21 February 2024


There are many filters that determine which data sets are included in, or excluded from, each release of the Chandra Source Catalog.

Release 2.1


Public ACIS timed-exposure mode observations in FAINT, VFAINT, FAINT_BIAS, or GRADED exposure modes are included. For observations obtained in Alternating Exposure (Interleaved) mode, only the long exposures are included.

The following ACIS observations are excluded:


Public HRC-I observations are included.


HRC-S observations are excluded.

Other Exclusions

  • All grating observations are excluded.
  • Moving target (solar system) observations are excluded.
  • Observations obtained with defocus < -0.1 mm or > +0.2 mm are excluded.
  • Observations obtained with sim_z_offset < -20.0 mm or > +20.0 mm are excluded.
  • The following observations that otherwise meet all of the other criteria are excluded: ObsIDs 984, 985, 1996, 2000, and 2594.
  • In a small number of cases, "exclusion regions" are created that reject all candidate detections from specific regions of a stacked observation field-of-view. These regions typically surround areas that include ACIS exclude windows in the individual observations comprising the stack (so that no meaningful detections will be present in these regions). In such cases, there will be no detection sensitivity for the stacked observation within the exclusion region. The following stacked observations include one or more exclusions regions: acisfJ0534316p220052_001, acisfJ0534322p215837_001, acisfJ0955234p690445_001, and acisfJ2144487p382120_001.

Additional Selection Criteria

There are a small number of additional criteria that an observation must meet in order to be selected for catalog processing:

  • The observation data set must have been processed through CXC Data System release 8.4.2 or later. This ensures that the data products required by the catalog processing are available. As a consequence, most observations obtained prior to January 29, 2000 are included in release 2.1 of the CSC; only ObsIDs 00243, 00255, and 00267 (all HRC-I observations of M31 obtained on 1999-11-30) obtained prior to this date are included.
  • The data set must have a good Verification and Validation (V&V) status. During V&V, the products are checked by CXC scientists to ensure data quality.
  • The data set must have a public release date prior no later than 2021-12-31T23:59:59.