Outer disc edge: properties of low frequency aperiodic variability in ultracompact interacting binaries by M. Veresvarska et al. on Tuesday 29 November

Flickering, and more specifically aperiodic broad-band variability, is an

important phenomenon used in understanding the geometry and dynamics of

accretion flows. Although the inner regions of accretion flows are known to

generate variability on relatively fast timescales, the broad-band variability

generated in the outer regions have mostly remained elusive due to their long

intrinsic variability timescales. Ultra-compact AM CVn systems are relatively

small when compared to other accreting binaries and are well suited to search

and characterise low frequency variability. Here we present the first low

frequency power spectral analysis of the ultracompact accreting white dwarf

system SDSS J1908$+$3940. The analysis reveals a low frequency break at $\sim

6.8 \times 10^{-7} $ Hz in the time-averaged power spectrum as well as a second

higher frequency component with characteristic frequency of $\sim 1.3 \times

10^{-4} $ Hz. We associate both components to the viscous timescales within the

disc through empirical fits to the power spectrum as well as analytical fits

using the fluctuating accretion disk model. Our results show that the low

frequency break can be associated to the disk outer regions of a geometrically

thin accretion flow. The detection of the low frequency break in SDSS

J1908$+$3940 provides a precedent for further detection of similar features in

other ultracompact accreting systems. More importantly, it provides a new

observable that can help constrain simulations of accretion flows.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.14338v1