Autoregressive modeling of the variability of an active galaxy



Many natural phenomena can be described by power-laws of the temporal or spatial correlations. The equivalent in frequency domain is the 1/f spectrum. A closer look at various natural data reveals more or less significant deviations from a 1/f characteristic. Such deviations are especially evident at low frequencies and less evident at high frequencies where spectra are very noisy. We exemplify such cases with a phenomenon offered by astrophysics. The X ray variability of the NGC 5506 galaxy can be better approximated by AR(1) – a first order autoregressive model, than by a 1/f model (long-range memory). The same spectra can be more or less easily confused and/or approximated by power-laws. A key step to detect non-power laws in the spectra, already suggested by Mandelbrot, is to average out the spectra.


V.V. Morariu

C. Vamoș
-Tiberiu Popoviciu Institute of Numerical Analysis, Romanian Academy

A. Pop

S.M. Soltuz
-Tiberiu Popoviciu Institute of Numerical Analysis, Romanian Academy


Autoregressive model, short-range correlation, galaxies.

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V.V. Morariu, C. Vamoş, A. Pop, Ş.M. Şoltuz, L. Buimaga-Iarinca, Autoregressive modeling of the variability of an active galaxyRomanian Journal of Physics, vol. 55 (2010) pp. 676-686



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