The Why & How of X-Ray Timing - HEASARC - NASA

Estimating Variability from observations• Find “area” A under curvein power spectrum,A = ∫ P dν ≈ ∑ j P j ∆ν,where P j are the PDSvalues, and ∆ν = 1 / T is theNyquist spacing.• Fractional RMS isr = √ A / • For coherent pulsations,f p = √ 2(P–2) / is the pulsed fraction, i.e.,(peak–mean)/mean