Scaling laws of quasi-periodic pulsations in solar flares

Abstract

Context. Quasi-periodic pulsations (QPPs) are a common feature of solar flares, but there has previously been a lack of observational evidence to support any of the theoretical models that might explain the origin of these QPPs. Aims. We aimed to determine if there are any relationships between the QPP period and other properties of the flaring region, using a previously assembled sample of flares with QPPs. If any relationships exist, then these can be compared with scaling laws for the theoretical QPP mechanisms. Methods. To obtain the flaring region properties, we made use of the Atmospheric Imaging Assembly (AIA) 1600 Å and Helioseismic and Magnetic Imager (HMI) data. The flare ribbons are visible in AIA 1600 Å images, and the positive and negative magnetic polarity ribbons can be distinguished and the magnetic properties determined in the HMI magnetograms. The ribbon properties calculated in this study were the ribbon separation distance, area, total unsigned magnetic flux, and average magnetic field strength. Only the flares that occurred within ±60° of the solar disc centre were included, which meant a sample of 20 flares with 22 QPP signals. Results. Positive correlations were found between the QPP period and the ribbon properties. The strongest correlations were with the separation distance and magnetic flux. Because these ribbon properties also correlate with the flare duration and because the relationship between the QPP period and flare duration may be influenced by observational bias, we also made use of simulated data to determine whether artificial correlations were introduced. These simulations show that although QPPs cannot be detected for certain combinations of QPP period and flare duration, this does not introduce an apparent correlation. Conclusions. There is evidence of relationships between the QPP period and flare ribbon properties, and in the future, the derived scaling laws between these properties can be compared to equivalent scaling laws for theoretical QPP mechanisms.