compute_fvar

gammapy.time.compute_fvar(flux, flux_err)

Calculate the fractional excess variance.

This method accesses the the FLUX and FLUX_ERR columns from the lightcurve data.

The fractional excess variance $F_{var}$, an intrinsic variability estimator, is given by

$$F_{var} = \sqrt{\frac{S^{2} - \bar{\sigma^{2}}}{\bar{x}^{2}}}.$$

It is the excess variance after accounting for the measurement errors on the light curve $\sigma$. $S$ is the variance.

Parameters

fluxQuantity

the measured fluxes

flux_errQuantity

the error on measured fluxes

Returns

fvar, fvar_errndarray

Fractional excess variance.

References

Vaughan2003

“On characterizing the variability properties of X-ray light curves from active galaxies”, Vaughan et al. (2003) https://ui.adsabs.harvard.edu/abs/2003MNRAS.345.1271V