gammapy.stats.compute_fpp(flux, flux_err, axis=0)[source]#

Calculate the point-to-point excess variance.

F_pp is a quantity strongly related to the fractional excess variance F_var implemented in compute_fvar; F_pp probes the variability on a shorter timescale.

For white noise, F_pp and F_var give the same value. However, for red noise, F_var will be larger than F_pp, as the variations will be larger on longer timescales.

It is important to note that the errors on the flux must be Gaussian.


The measured fluxes.


The error on measured fluxes.

axisint, optional

Axis along which the excess variance is computed. Default is 0.

fpp, fpp_errndarray

Point-to-point excess variance.



“X-Ray Spectral Variability and Rapid Variability of the Soft X-Ray Spectrum Seyfert 1 Galaxies Arakelian 564 and Ton S180”, Edelson et al. (2002), equation 3,