Searching for rapid pulsations in solar flare X-ray data

Abstract: Most studies of quasi-periodic pulsations in solar flares have identified characteristic periods in the 5 - 300s range. Due to observational limitations there have been few attempts to probe the < 5s period regime and understand the prevalence of such short-period quasi-periodic pulsations. However, the Fermi Gamma-ray Burst Monitor (GBM) has observed approximately 1500 solar flares to date in high cadence 16 Hz burst mode, providing us with an opportunity to study short-period quasi-periodic pulsations at X-ray energies. We systematically analyse every solar flare observed by Fermi/GBM in burst mode, estimating the prevalence of quasi-periodic pulsations in multiple X-ray energy bands. To better understand these results, we complement this with analysis of synthetic solar flare lightcurves, both with and without oscillatory signals present. Using these synthetic lightcurves, we can understand the likely false alarm and true positive rates in the real solar GBM data. We do not find strong evidence for widespread short-period quasi-periodic pulsations, indicating either a low base occurrence rate of such signatures or that their typical signal-to-noise ratios must be low - less than 1 - in Fermi/GBM data. Finally, we present a selection of the most interesting potential quasi-periodic pulsation events that were identified in the GBM solar X-ray data.