Instrument Response Functions (DL3)

Instrument Response Functions

Typically the IRFs are stored in the form of multidimensional tables giving the response functions such as the distribution of gamma-like events or the probability density functions of the reconstructed energy and position.

For a more detailed definition of the response function you are invited to read IRF Theory.

gammapy.irf handles the following instrument response functions (IRFs):

• Effective area (AEFF)

• Energy Dispersion (EDISP)

• Point Spread Function (PSF)

• Background (BKG)

Most of the formats defined at IRFs are supported. At the moment, there is 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.

IRF axis naming

In the IRF classes we use the following axis naming convention:

Variable	Definition
energy	Reconstructed energy axis (\(E\) in IRF Theory)
energy_true	True energy axis (\(E_{\rm true}\) in IRF Theory)
offset	Field of view offset from center (\(p_{\rm true}\) in IRF Theory)
fov_lon	Field of view longitude
fov_lat	Field of view latitude
migra	Energy migration (\(\mu\) in IRF Theory)
rad	Offset angle from source position (\(\delta p\) in IRF Theory)

Using gammapy.irf

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

• IRF Theory
• Effective area
• Energy Dispersion
• Point Spread Function
• Background

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