Point Spread Function

As a function of of true energy and offset angle (PSF_TABLE)

The PSF3D class represents the radially symmetric probability density of the angular separation between true and reconstructed directions \(\delta p = p_{\rm true} - p\) (or rad), as a function of true energy and offset angle from the field of view center (\(PSF(E_{\rm true}, \delta p|p_{\rm true})\) in IRF Theory).

Its format specifications are available in PSF_TABLE.

This is the format in which IACT DL3 PSFs are usually provided, as an example:

"""Plot a PSF from the HESS DL3 data release 1."""
import matplotlib.pyplot as plt
from gammapy.irf import PSF3D

filename = "$GAMMAPY_DATA/hess-dl3-dr1/data/hess_dl3_dr1_obs_id_020136.fits.gz"
psf = PSF3D.read(filename, hdu="PSF")
psf.peek()
plt.show()

(png, hires.png, pdf)

../_images/plot_psf.png

Additional PSF classes

The remaining IRF classes implement:

  • EnergyDependentMultiGaussPSF a PSF whose probability density is parametrised by the sum of 1 to 3 2-dimensional gaussian (definition at PSF_3GAUSS);

  • PSFKing a PSF whose probability density is parametrised by the King function (definition at PSF_KING);

  • PSFKernel a PSF that can be used to convolve WcsNDMap objects;

  • PSFMap a four-dimensional Map storing a PSFKernel for each sky position.