Significance testing for quasi-periodic pulsations in solar and stellar flares

¹ Department of PhysicsUniversity of Warwick, Coventry, CV4 7AL, UK
e-mail: c.e.pugh@warwick.ac.uk
² Institute of Advanced Study, University of Warwick, Coventry, CV4 7HS, UK
³ St. Petersburg Branch, Special Astrophysical Observatory, Russian Academy of Sciences, 196140, St. Petersburg, Russia

Received: 10 February 2017
Accepted: 20 March 2017

Abstract

The robust detection of quasi-periodic pulsations (QPPs) in solar and stellar flares has been the topic of recent debate. In light of this, we have adapted a method described by Vaughan (2005, A&A, 431, 391) to aid with the search for QPPs in flare time series data. The method identifies statistically significant periodic signals in power spectra, and properly accounts for red noise as well as the uncertainties associated with the data. We show how the method can be further developed to be used with rebinned power spectra, allowing us to detect QPPs whose signal is spread over more than one frequency bin. An advantage of these methods is that there is no need to detrend the data prior to creating the power spectrum. Examples are given where the methods have been applied to synthetic data, as well as real flare time series data with candidate QPPs from the Nobeyama Radioheliograph. These show that, despite the transient nature of QPPs, peaks corresponding to the QPPs can be seen at a significant level in the power spectrum without any form of detrending or other processing of the original time series data, providing the background trends are not too steep.