The influence of outflows on the 1/f-like luminosity fluctuations

TL;DR

This paper investigates how outflows affect the luminosity fluctuations in accretion systems, revealing that outflows modify the power spectral density and can be used to infer outflow strength from observational data.

Contribution

It extends Lyubarskii's scheme by incorporating outflows, deriving new power spectral density relations for different accretion flow types, and linking spectral features to outflow strength.

Findings

Power spectrum follows a specific power-law depending on outflow strength.

Neutrino-cooled discs have larger power-law indices than photon-cooled discs.

Outflow strength can potentially be estimated from observed power spectra.

Abstract

In accretion systems, outflows may have significant influence on the luminosity fluctuations. In this paper, following the Lyubarskii's general scheme, we revisit the power spectral density of luminosity fluctuations by taking into account the role of outflows. Our analysis is based on the assumption that the coupling between the local outflow and inflow is weak on the accretion rate fluctuations. We find that, for the inflow mass accretion rate $\dot M \propto r^{s}$, the power spectrum of flicker noise component will present a power-law distribution $p(f) \propto f^{-(1+4s/3)}$ for advection-dominated flows. We also obtain descriptions of $p(f)$ for both standard thin discs and neutrino-cooled discs, which show that the power-law index of a neutrino-cooled disc is generally larger than that of a photon-cooled disc. Furthermore, the obtained relationship between $p(f)$ and $s$ indicates the possibility of evaluating the strength of outflows by the power spectrum in X-ray binaries and gamma-ray bursts. In addition, we discuss the possible influence of the outflow-inflow coupling on our results.