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Statistical Signatures of Nanoflare Activity. II. A Nanoflare Explanation for Periodic Brightenings in Flare Stars Observed by NGTS

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Version 2 2021-06-10, 09:29
Version 1 2020-11-03, 14:00
journal contribution
posted on 2021-06-10, 09:28 authored by Christopher J Dillon, David B Jess, Michail Mathioudakis, Christopher A Watson, James A Jackman, Peter J Wheatley, Michael R Goad, Sarah L Casewell, David R Anderson, Matthew R Burleigh, Liam Raynard, Richard West
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 a period from 1 to 1000 s 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 magnetohydrodynamic wave behavior. However, we propose that a series of continuous nanoflares, based upon a power-law distribution, can provide a similar periodic signal in the associated time series. Adapting previous statistical analyses of solar nanoflare signals, we find the first statistical evidence for stellar nanoflare signals embedded within the noise envelope of M-type stellar lightcurves. Employing data collected by the Next Generation Transit Survey (NGTS), we find evidence for stellar nanoflare activity demonstrating a flaring power-law index of 3.25 ± 0.20, alongside a decay timescale of 200 ± 100 s. We also find that synthetic time series, consistent with the observations of dMe flare star lightcurves, are capable of producing quasi-periodic signals in the same frequency range as p-mode signals, despite being purely composed of impulsive signatures. Phenomena traditionally considered a consequence of wave behavior may be described by a number of high-frequency but discrete nanoflare energy events. This new physical interpretation presents a novel diagnostic capability, by linking observed periodic signals to given nanoflare model conditions.

History

Citation

ApJ 904 109

Author affiliation

Department of Physics and Astronomy

Version

  • VoR (Version of Record)

Published in

The Astrophysical Journal

Volume

904

Issue

2

Publisher

IOP Publishing for American Astronomical Society

issn

0004-637X

Acceptance date

2020-10-07

Copyright date

2020

Available date

2021-06-10

Language

en

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