Effective Area

The proposed effective area format follows mostly the OGIP effective area format document.

For the moment, the format for the effective area works to satisfactory detail. Nevertheless, for instance the energy threshold variation across the FoV is not taken into account. However, since the threshold definitions are currently non-unified an inclusion of this variation is still arbitrary and subject to analysis chain. In addition, this feature is currently not supported in current open source tools. We therefore keep the optional opportunity to add an individual extension listing the energy threshold varying across the FoV. This will likely be included in future releases.

aeff_2d format

The effective area information is saved as a BINTABLE HDU with required columns listed below.

Columns:

  • THETA_LO, THETA_HI – ndim: 1, unit: deg
    • Field of view offset axis
  • ENERG_LO, ENERG_HI – ndim: 1, unit: TeV
    • Energy axis
  • EFFAREA – ndim: 2, unit: none
    • Effective area value as a function of true energy
  • EFFAREA_RECO – ndim: 2, unit: deg
    • Effective area value as a function of reco energy

Recommended axis order: ENERGY, THETA

Header keywords:

In addition to the standard header keywords the recommended energy range for the observation corresponding to the effective area file is stored in two additional header keywords. Another optional header keyword contains the theta squared cut that was applied in the case of a effective area generation for point-like sources.

  • OBS_ID type: int
    • Observation ID, run number
  • LO_THRES type: float, unit: TeV
    • Low energy threshold
  • HI_THRES type: float, unit: TeV
    • High energy threshold
  • RAD_MAX type: float, unit: deg
    • On region radius for point-like observations

An example file is provided here.