The impact of periastron passage on the X-ray and optical properties of the Symbiotic System R Aquarii

TL;DR

This study analyzes 22 years of X-ray and optical data of the symbiotic system R Aquarii, revealing how its X-ray emission components and accretion rates vary with orbital phase, especially near periastron.

Contribution

It introduces a reflection model to dissect X-ray spectra of R Aqr and studies the temporal evolution of its components and accretion parameters over two decades.

Findings

X-ray fluxes increase near periastron passage.

The boundary layer and reflection components show correlated flux increases.

Mass-accretion rate and wind accretion efficiency are relatively stable with median values.

Abstract

Multi-epoch Chandra and XMM-Newton observations of the symbiotic system R Aquarii (R Aqr) spanning 22 yr are analysed by means of a reflection model produced by an accretion disc. This methodology helps dissecting the contribution from different components in the X-ray spectra of R Aqr: the soft emission from the jet and extended emission, the heavily-extinguished plasma component of the boundary layer and the reflection contribution, which naturally includes the 6.4 keV Fe fluorescent line. The evolution with time of the different components is studied for epochs between 2000 Sep and 2022 Dec, and it is found that the fluxes of the boundary layer and that of the reflecting component increase as the stellar components in R Aqr approach periastron passage, a similar behaviour is exhibited by the shocked plasma produced by the precessing jet. Using publicly available optical and UV data we are able to study the evolution of the mass-accretion rate $\dot{M}_\mathrm{acc}$ and the wind accretion efficiency $\eta$ during periastron. These exhibit a small degree of variability with median values of $\dot{M}_\mathrm{acc}$=7.3$\times10^{-10}$ M$_\odot$ yr$^{-1}$ and $\eta$=7$\times10^{-3}$. We compare our estimations with predictions from a modified Bondi-Hoyle-Lyttleton accretion scenario.