# irf - Instrument response functions¶

## Introduction¶

gammapy.irf handles instrument response functions (IRFs):

• Effective area (AEFF)

• Energy dispersion (EDISP)

• Template background (BKG)

Most of the formats defined at IACT IRFs are supported. Otherwise, at the moment, there is very little support for Fermi-LAT or other instruments.

Most users will not use gammapy.irf directly, but will instead use IRFs as part of their spectrum, image or cube analysis to compute exposure and effective EDISP and PSF for a given dataset.

Most (at some point maybe all) classes in gammapy.irf have an gammapy.utils.nddata.NDDataArray as data attribute to support interpolation.

## Getting Started¶

See cta.html for an example how to access IACT IRFs.

## PSF¶

The TablePSF and EnergyDependentTablePSF classes represent radially-symmetric PSFs where the PSF is given at a number of offsets.

The PSFKernel represents a PSF kernel.

(png, hires.png, pdf)

## Energy Dispersion¶

The EnergyDispersion class represents an energy migration matrix (finite probabilities per pixel) with y=log(energy_reco).

The EnergyDispersion2D class represents a probability density with y=energy_reco/energy_true that can also have a FOV offset dependence.

(png, hires.png, pdf)

## Using gammapy.irf¶

If you’d like to learn more about using gammapy.irf, read the following sub-pages:

## Reference/API¶

### gammapy.irf Package¶

Instrument response functions (IRFs).

#### Functions¶

 load_cta_irfs(filename) load CTA instrument response function and return a dictionary container. make_mean_psf(observations, position[, …]) Compute mean energy-dependent PSF. make_psf(observation, position[, energy, rad]) Make energy-dependent PSF for a given source position.

#### Classes¶

 Background2D(energy_lo, energy_hi, …[, …]) Background 2D. Background3D(energy_lo, energy_hi, …[, …]) Background 3D. EDispKernel(e_true_lo, e_true_hi, e_reco_lo, …) Energy dispersion matrix. EffectiveAreaTable(energy_lo, energy_hi, data) Effective area table. EffectiveAreaTable2D(energy_lo, energy_hi, …) 2D effective area table. EnergyDependentMultiGaussPSF(energy_lo, …) Triple Gauss analytical PSF depending on energy and theta. EnergyDependentTablePSF(energy, rad[, …]) Energy-dependent radially-symmetric table PSF (gtpsf format). EnergyDispersion2D(e_true_lo, e_true_hi, …) Offset-dependent energy dispersion matrix. IRFStacker(list_aeff, list_livetime[, …]) Stack instrument response functions. PSF3D(energy_lo, energy_hi, offset, rad_lo, …) PSF with axes: energy, offset, rad. PSFKing(energy_lo, energy_hi, offset, gamma, …) King profile analytical PSF depending on energy and offset. TablePSF(rad, psf_value[, interp_kwargs]) Radially-symmetric table PSF.