compute_fpp

gammapy.stats.compute_fpp(flux, flux_err, axis=0)

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.

Parameters

fluxQuantity

The measured fluxes.

flux_errQuantity

The error on measured fluxes.

axisint, optional

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

Returns

fpp, fpp_errndarray

Point-to-point excess variance.

References

Edelson2002

“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, https://iopscience.iop.org/article/10.1086/323779