PSF_KING¶
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:
ENERG_LO
,ENERG_HI
– ndim: 1, unit: TeV- True energy axis
THETA_LO
,THETA_HI
– ndim: 1, unit: deg- Field of view offset axis (see Field of view)
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:
As explained in HDU classes, the following header keyword should be used to declare the type of HDU:
HDUDOC
= ‘https://github.com/open-gamma-ray-astro/gamma-astro-data-formats’HDUVERS
= ‘0.3’HDUCLASS
= ‘GADF’HDUCLAS1
= ‘RESPONSE’HDUCLAS2
= ‘PSF’HDUCLAS3
= ‘FULL-ENCLOSURE’HDUCLAS4
= ‘PSF_KING’
Example data file: TODO