This is a PSF FITS format we agree on for IACTs. This file contains the offset- and energy-dependent table distribution of the PSF.

This format is almost identical to the OGIP radial PSF format. The differences are that we don’t have the dependency on azimuthal field of view position, the units are different and the recommended axis order is different (to have uniformity across axis order in the IACT DL3 IRFs).


  • ENERG_LO, ENERG_HI – ndim: 1, unit: TeV
    • True energy axis
  • THETA_LO, THETA_HI – ndim: 1, unit: deg
  • RAD_LO, RAD_HI – ndim: 1, unit: deg
    • Offset angle from source position
  • RPSF – ndim: 3, unit: sr^-1

Recommended axis order: ENERGY, THETA, RAD.

Header keywords:

As explained in HDU classes, the following header keyword should be used to declare the type of HDU:

Example data file: TODO