# Autoregressive modeling of the variability of an active galaxy

## Abstract

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.

## Authors

V.V. Morariu
– National Institute of Research and Development for Isotopic and Molecular Technologies,
Department of Molecular and Biomolecular Physics, Cluj-Napoca, Romania
– Academy of Romanian Scientists, 54, Splaiul Independentei, Sector 5,  Bucharest, Romania

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

A. Pop

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

L. Buimaga-Iarinca
– National Institute of Research and Development for Isotopic and Molecular Technologies,
Department of Molecular and Biomolecular Physics, Cluj-Napoca, Romania

## Keywords

Autoregressive model, short-range correlation, galaxies.

## Cite this paper as:

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

## PDF

##### Journal

Romanian Journal of Physics

1221-146X

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