Flickering around the outburst cycle in Kepler dwarf novae

TL;DR

This study analyzes Kepler light curves of dwarf novae to examine flickering behavior around outburst cycles, revealing hysteresis effects in flickering strength and spectral index that align with the disk instability model.

Contribution

It provides the first detailed analysis of flickering hysteresis in dwarf novae using high-quality Kepler data, confirming previous findings and introducing new hysteresis observations.

Findings

Flickering strength is constant above a brightness threshold and increases at fainter magnitudes.

Hysteresis observed: flickering is stronger during decline than rise at the same magnitude.

Spectral index also shows hysteresis, consistent with the flickering strength behavior.

Abstract

Taking advantage of the unparallel quantity and quality of high cadence Kepler light curves of several dwarf novae, the strength of the flickering and the high frequency spectral index of their power spectra are investigated as a function of magnitude around the outburst cycle of these systems. Previous work suggesting that the flickering strength (on a magnitude scale) is practically constant above a given brightness threshold and only rises at fainter magnitudes is confirmed for most of the investigated systems. As a new feature, a hysteresis in the flickering strength is seen in the sense that at the same magnitude level flickering is stronger during decline from outburst than during the rise. A similar hysteresis is also seen in the spectral index. In both cases, it can qualitatively be explained under plausible assumptions within the DIM model for dwarf nova outbursts.