Last modified: 23 May 2018


[Updated]Observation Selection

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

Release 2


Public ACIS timed-exposure mode observations in FAINT, VFAINT, FAINT_BIAS, or GRADED exposure modes are included.

The following ACIS observations are excluded:


HRC-I observations are included in Release 2.0.


HRC-S observations are excluded from Release 2.0.

Other exclusions
  • All grating observations are excluded.
  • Moving target (solar system) observations are excluded.
  • Observations obtained with with defocus <-0.1 mm or >+0.2 mm are excluded.
  • Observations obtained with with sim_z_offset <-20.0 mm or >+20.0 mm are excluded.

Selection Criteria

There are also a number of criteria that an observation interval (OBI) must meet in order to be selected for catalog processing:


Each observation interval (OBI) chosen by the observation selection process is checked to see if it overlaps with other such intervals such that their pointing directions are within 60″ of each other. Such co-aligned observations are grouped into 'stacks'. For more information see the Catalog Organization section.