Fluctuation dynamo at finite correlation times and the Kazantsev spectrum

Abstract

Fluctuation dynamos are generic to astrophysical systems. The only analytical model of the fluctuation dynamo is Kazantsev model which assumes a delta-correlated in time velocity field. We derive a generalized model of fluctuation dynamo with finite correlation time, $\tau$, using renovating flows. For $\tau \to 0$, we recover the standard Kazantsev equation for the evolution of longitudinal magnetic correlation, $M_L$. To the next order in $\tau$, the generalized equation involves third and fourth spatial derivatives of $M_L$. It can be recast using the Landau-Lifschitz approach, to one with at most second derivatives of $M_L$. Remarkably, we then find that the magnetic power spectrum, remains the Kazantsev spectrum of $M(k)\propto k^{3/2}$, in the large $k$ limit, independent of $\tau$.

arXiv comment5 pages, Published in ApJL

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