Observational evidence for matter propagation in accretion flows

TL;DR

This study uses simultaneous X-ray and optical observations of intermediate polars to investigate matter propagation in accretion flows, revealing correlated flux variability and a measurable propagation time consistent with theoretical models.

Contribution

It provides observational evidence supporting the propagating fluctuations model in accretion flows of intermediate polars, including a direct measurement of matter travel time.

Findings

Optical and X-ray fluxes are correlated with <1 sec lag.

Optical emission largely results from reprocessing of X-ray luminosity.

Measured matter travel time (~7 sec) matches theoretical expectations.

Abstract

We study simultaneous X-ray and optical observations of three intermediate polars EX Hya, V1223 Sgr and TV Col with the aim to understand the propagation of matter in their accretion flows. We show that in all cases the power spectra of flux variability of binary systems in X-rays and in optical band are similar to each other and the majority of X-ray and optical fluxes are correlated with time lag <1 sec. These findings support the idea that optical emission of accretion disks, in these binary systems,largely originates as reprocessing of X-ray luminosity of their white dwarfs. In the best obtained dataset of EX Hya we see that the optical lightcurve unambiguously contains some component, which leads the X-ray emission by ~7 sec. We interpret this in the framework of the model of propagating fluctuations and thus deduce the time of travel of the matter from the innermost part of the truncated accretion disk to the white dwarf surface. This value agrees very well with the time expected for matter threaded onto the magnetosphere of the white dwarf to fall to its surface. The datasets of V1223 Sgr and TV Col in general confirm these findings,but have poorer quality.