X-ray Variability of SS 433: Evidence for Supercritical Accretion

TL;DR

This study analyzes X-ray variability in SS 433, revealing a flat-topped noise spectrum likely linked to supercritical accretion processes and jet activity, with implications for disk and jet dynamics.

Contribution

It provides the first detailed power spectrum of SS 433's X-ray variability, identifying a flat portion indicative of supercritical accretion disk behavior.

Findings

Confirmed flat-topped noise in the power spectrum at specific frequencies

Suggested the variability is influenced by supercritical accretion and jet activity

Indicated the disk's viscous time decreases rapidly in supercritical zones

Abstract

We study the X-ray variability of SS433 based on data from the ASCA observatory and the MAXI and RXTE/ASM monitoring missions. Based on the ASCA data, we have constructed the power spectrum of SS433 in the frequency range from $10^{-6}$ to 0.1 Hz, which confirms the presence of a flat portion (flat-topped noise) in the spectrum at frequencies $3\times 10^{-5}$ - $10^{-3}$ Hz. The periodic variability (precession, nutation, eclipses) begins to dominate significantly over the stochastic variability at lower frequencies, which does not allow the stochastic variability to be studied reliably. The best agreement with the observations is reached by the model with the flat portion extending to $9.5\times10^{-6}$ Hz and a power-law spectrum with index of 2.6 below that frequency. The jet nutation with a period of about three days suggests that the time for the passage of material through the disk is less than this value. Therefore, at frequencies below $4\times10^{-6}$ Hz, the power spectrum probably does not reflect the disk structure. It may depend on other factors, for example, a variable mass accretion rate supplied by the donor. The flat portion may arise from a rapid decrease in the viscous time in the supercritical or radiative disk zones. It could be related to the variability of the X-ray jets that are formed in the supercritical region.