# Variation of mass accretion rate onto the white dwarf in the dwarf nova VW Hyi in quiescence

## TL;DR

This study analyzes X-ray data of the dwarf nova VW Hyi in quiescence, revealing that the mass accretion rate declines over time since outburst, contrary to standard disc instability model predictions.

## Contribution

It provides observational evidence of declining mass accretion rates in VW Hyi during quiescence, challenging existing theoretical models of disc behavior.

## Key findings

- Mass accretion rate shows a clear decline with time since outburst.
- Observed spectra are well represented by multi-temperature thermal plasma models.
- Contradicts the prediction that accretion rate should increase during quiescence.

## Abstract

We have analysed a series of Suzaku data and one dataset of XMM-Newton of the SU UMa type dwarf nova VW Hyi in optical quiescence. The observed spectra in the 0.2-10 keV band are moderately well represented by multi-temperature thermal plasma emission models with a maximum temperature of 5-9 keV and bolometric luminosity of 2.4-5.2 $\times$ 10$^{30}$ erg s$^{-1}$. The mass accretion rate derived from the hard X-ray spectra does not show any clear trend as a function of time since the last superoutburst, in contradiction to theoretical predictions of the disc behaviour of a SU UMa type dwarf nova. The mass accretion rate, on the other hand, shows a clear declining trend with time since the last outburst (including the superoutburst). The rate of decline is of the same order as that evaluated from the hard X-ray light curves of the other two dwarf novae SS Cyg and SU UMa. The standard disc instability model, on the other hand, predicts that the mass accretion rate should increase throughout the optically-quiescent phase. We need further observation and theoretical consideration to resolve this discrepancy.