Correlating the non-linear time series and spectral properties of IGR J17091-3624: is it similar to GRS 1915+105?

Abstract

Using the correlation integral method, we explore the non-linear properties of IGR J17091-3624 by comparing the underlying behaviour to GRS 1915+105. We find that while GRS 1915+105 is known to reveal a combination of fractal (or even chaotic) and stochastic behaviours depending on its temporal class, IGR J17091-3624 mostly shows stochastic behaviour. Therefore, although several observations find that IGR J17091-3624 is similar to GRS 1915+105, and that they have temporal classes in common, the underlying non-linear time series analyses offer a different view. Nevertheless, the ratio of the Poisson noise to rms variation for IGR J17091-3624 turns out to be high, suggesting that it is dominated by Poisson noise. Hence it might plausibly lead to the suppression of its non-linear properties, if there is any. Indeed, IGR J17091-3624 is a very faint source compared with GRS 1915+105. However, by increasing the time bin, some of the temporal classes of IGR J17091-3624 show deviation from stochasticity, indicating the plausibility of a higher fractal dimension. Along with spectral analysis, overall IGR J17091-3624 seems to reveal three different accretion classes: slim, Keplerian and advective accretion discs.