Statistical Signatures of Nanoflare Activity II : A Nanoflare Explanation for Periodic Brightening in Flare Stars

Several studies have documented periodic and quasi-periodic signals from the time series of dMe flare stars and other stellar sources. Such periodic signals, observed within quiescent phases (i.e., devoid of larger-scale microflare or flare activity), range in period from 1-1000 seconds and hence have been tentatively linked to ubiquitous p-mode oscillations generated in the convective layers of the star. As such, most interpretations for the observed periodicities have been framed in terms of magneto-hydrodynamic wave behaviour. However, we propose that a series of continuous nanoflares, based upon a powerlaw distribution, can provide a similar periodic signal in the associated synthetic time series. Monte Carlo simulations, embodying the nanoflare signals and modelled noise profiles, produces a time series consistent with previous observations of dMe flare star lightcurves. Through an examination of nanoflare decay timescales and differing powerlaw indices, we provide evidence that periodic signals alongside characteristic power spectrum features found in stellar time series can be explained by low-energy nanoflares embedded within the noise envelope of a stellar lightcurve.

The NGTS is the ideal observational companion for these simulations, due to its high cadence, and months worth of data giving excellent frequency resolution. We have carried out promising feature mapping between our nanoflare simulations and M-type lightcurves. We also found a null result in a A-type lightcurve, as we would expect for a non flare-active star. This work holds the thrilling and novel capability of stellar nanoflaring diagnosis.