psf_king
format¶
The King function parametrisations for PSFs has been in use in astronomy as an analytical PSF model for many instruments, for example by the Fermi-LAT (see 2013ApJ…765…54A).
The distribution has two parameters GAMMA
\(\gamma\) and SIGMA
\(\sigma\)
and is given by the following formula:
\[dP/d\Omega(r,\sigma,\gamma) =
\frac{1}{2\pi\sigma^2}
\left(1-\frac{1}{\gamma}\right)
\left(1+\frac{r^2}{2\gamma\sigma^2}\right)^{- \gamma}\]
This formula integrates to 1 (see Introduction).
Columns:
THETA_LO
,THETA_HI
– ndim: 1, unit: deg- Field of view offset axis
ENERG_LO
,ENERG_HI
– ndim: 1, unit: TeV- Energy axis
GAMMA
– ndim: 2, unit: none- Model parameter (see formula above)
SIGMA
– ndim: 2, unit: deg- Model parameter (see formula above)
Recommended axis order: ENERGY
, THETA
Header keywords: none
Example data file: TODO: add HESS HAP example file as soon as available.