A Large-Scale Search for Evidence of Quasi-Periodic Pulsations in Solar Flare X-ray Emission

The nature of quasi-periodic pulsations in solar flares is poorly constrained, and critically the general prevalence of such signals in solar flares is unknown. We present the results of a large-scale, statistically robust search for evidence of signals consistent with quasi-periodic pulsations in solar flares, focusing on the 1 - 300s timescale. We analyse 675 M- and X-class flares observed by GOES in 1-8A soft X-rays between 2011 February 1 and 2015 December 31. Additionally, we analyse 209 events in the same time interval observed by Fermi/GBM in 15-25 keV X-rays. We use a novel model comparison approach, testing three models applied to the Fourier power spectra of each flare. From this we determine whether there is evidence for a substantial enhancement in the Fourier domain that may be consistent with a QPP signature. Our findings are that 30% of GOES events and 16% of Fermi/GBM events show signatures consistent with classical interpretations of QPP. The remaining events are adequately described by single power-law or broken power-law Fourier power spectra. For both instruments, a preferred characteristic timescale of 5-30 s was found, with no dependence on flare magnitude in GOES, and weak dependence in GBM. We also show that, for events where a detection occurred in both Fermi/GBM and GOES datasets, similar characteristic timescales were found with both instruments. We discuss the implications of these results for our understanding of solar flares and possible QPP mechanisms.