# irf - Instrument response functions¶

## Introduction¶

gammapy.irf handles instrument response functions (IRFs):

• Effective area (AEFF)
• Energy dispersion (EDISP)
• Point spread function (PSF)

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_1dc_introduction.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¶

 multi_gauss_psf_kernel(psf_parameters[, …]) Create multi-Gauss PSF kernel.

#### Classes¶

 Background2D(energy_lo, energy_hi, …[, …]) Background 2D. Background3D(energy_lo, energy_hi, …[, …]) Background 3D. BgRateTable(energy_lo, energy_hi, data) Background rate table. CTAIrf([aeff, edisp, psf, bkg, ref_sensi]) CTA instrument response function container. CTAPerf([aeff, edisp, psf, bkg, sens, rmf]) CTA instrument response function container. 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). EnergyDispersion(e_true_lo, e_true_hi, …) Energy dispersion matrix. EnergyDispersion2D(e_true_lo, e_true_hi, …) Offset-dependent energy dispersion matrix. GaussPSF([sigma]) Extension of Gauss2D PDF by PSF-specific functionality. HESSMultiGaussPSF(source) Multi-Gauss PSF as represented in the HESS software. IRFStacker(list_aeff, list_livetime[, …]) Stack instrument response functions. PSF3D(energy_lo, energy_hi, offset, rad_lo, …) PSF with axes: energy, offset, rad. PSF3DChecker(psf[, d_norm, …]) Automated quality checks for gammapy.irf.PSF3D. PSFKing(energy_lo, energy_hi, offset, gamma, …) King profile analytical PSF depending on energy and offset. Psf68Table(energy_lo, energy_hi, data) Background rate table. SensitivityTable(energy_lo, energy_hi, data) Sensitivity table. TablePSF(rad, dp_domega[, spline_kwargs]) Radially-symmetric table PSF.