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Last modified: 13 December 2012

URL: http://cxc.harvard.edu/csc/columns/ebands.html

Energy Bands


The energy bands used for ACIS observations in the Chandra Source Catalog are split into two categories: source detection energy bands and science energy bands. Source detection energy bands are used only in the Detect Pipeline of catalog processing to detect sources, and are chosen to maximize the efficiency of the source detection process for different kinds of sources observed using the back- and front-side illuminated ACIS CCDs. Science energy bands are used for all science analyses and are chosen to maximize the scientific utility of the catalog. Since the HRC does not have significant energy resolution, there is a single broad energy band for both source detection and science.

Many of the CSC source properties are reported separately for each of the five science energy bands, e.g., the source flux quantity 'flux_aper' appears five times: flux_aper_b, flux_aper_u, flux_aper_s, flux_aper_m, flux_aper_h. In the Master Sources Table, source properties in the following CSC science categories are reported per science energy band: Source Fluxes, Source Significance, and Source Variability. In the Source Observations Table, the CSC science categories are: Position and Position Errors, Source Significance, Source Extent and Errors, Source Fluxes, and Source Variability.

For calculating exposure and instrument maps, PSFs, ARFs, and other quantities that require a single energy to be determined, an effective energy for each energy band was produced. They are listed below; for details on the calculations which led to the CSC effective band energies, see Appendix A of the CSC Requirements document.

ACIS Science Energy Bands and Effective Energies:

  • broad band (b): 0.5-7.0 keV
    2.3 keV
  • ultrasoft (u): 0.2-0.5 keV
    0.4 keV
  • soft (s): 0.5-1.2 keV
    0.92 keV
  • medium (m): 1.2-2.0 keV
    1.56 keV
  • hard (h): 2.0-7.0 keV
    3.8 keV

ACIS Source Detection Energy Bands and Effective Energies:

  • broad band (B): 0.5-7.0 keV
    2.3 keV
  • soft (S): 0.5-1.2 keV
    0.92 keV
  • medium (M): 1.2-2.0 keV
    1.56 keV
  • hard (H): 2.0-7.0 keV
    3.8 keV

HRC source detection and science energy band: The broad energy band corresponds approximately to photon energies 0.1-10 keV and is designated "w" to distinguish it from the ACIS broad band (b). The effective energy for the HRC energy band is 1.5 keV.

The broad bands for ACIS and HRC were chosen to cover the entire range in energy to which the telescope and detectors are sensitive. The ACIS soft, medium, and hard narrow bands were chosen to be used for images, source detection, flux measurements, and hardness ratios, based on the detector's spectral resolution capability and sensitivity. The ACIS ultrasoft science band was considered desirable for study of super soft sources.


Last modified: 13 December 2012
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