Similarities and differences between solar and stellar flare pulsation processes

TL;DR

Quasi-periodic pulsations (QPPs) in solar and stellar flares provide a diagnostic bridge between solar-scale processes and stellar-scale magnetic activity. The paper synthesizes detection methods and statistical properties from GOES, STIX, and Fermi solar data and Kepler, TESS, XMM-Newton, and Chandra stellar data, complemented by forward modeling of hydrodynamic loop oscillations. It finds that solar QPPs have $P \sim 10$–$60$ s with correlations $P \propto \tau^{0.7}$ and $P \propto d^{0.6}$, while stellar QPPs show $P \sim 10$–$100$ min with no strong correlation to global stellar parameters, and damping times scale with periods. Forward modeling reproduces observed light curves in both regimes, supporting a shared wave-based mechanism (e.g., slow magnetosonic waves or oscillatory reconnection) and implying larger loops and stronger fields in stars. The work highlights a continuum of magnetic activity from the Sun to active stars and provides constraints for future surveys and theoretical models of flare pulsations.

Abstract

Quasi-periodic pulsations (QPPs) are oscillatory signatures commonly detected in the light curves of solar and stellar flares, offering valuable diagnostics of the underlying magnetic and plasma processes. This review compares the observational characteristics, detection methods, and physical interpretations of QPPs in both solar and stellar contexts. Solar flare QPPs, extensively studied in X-rays and EUV bands using instruments such as GOES, STIX, and Fermi, display typical periods of tens of seconds and show correlations with flare duration and magnetic loop length. Stellar QPPs, observed in X-rays and white light by missions such as Kepler, TESS, and XMM-Newton, exhibit much longer periods - ranging from minutes to hours - consistent with larger-scale magnetic structures in more active stars. Despite differences in scale and observing band, statistical and comparative studies reveal common scaling relations and damping behaviors, suggesting that both solar and stellar QPPs are manifestations of the same fundamental mechanisms, likely magnetohydrodynamic oscillations or oscillatory reconnection within flare loops. The comparison underscores a continuity between solar and stellar magnetic activity, linking the solar detailed physical processes to stellar-scale phenomena and providing constraints for future models and surveys.

Figures (8)

• Figure 1: Flare light curve showing quasi-periodic pulsations. Examples of AFINO analysis applied to a solar M3.4 flare. The left panel (a) shows the 1–8 Å lightcurve (red) and its associated time derivative (gray). A corresponding Fourier power spectrum of the red lightcurve is plotted (black) in the right panel (b), together with a model fit (blue). The dashed gray lines mark the 2.5% and 97.5% quantiles relative to the power-law component of each model to help illustrate enhanced peaks in the spectra. (From Hayes2020a).
• Figure 2: Histogram of identified QPP periods from the statistical survey of X-, M-, and C-class solar flares. The best-fit log-normal distribution (inset) has a mean period of 21.6s (red dashed line). (From Hayes2020a).
• Figure 3: Scatter plots of QPP periods with (a) flare size and (b) flare duration. In the hatched region duration–period combinations cannot be detected. A power-law fit is shown in panel b) (dashed line). The correlation coefficients are labeled in the bottom right of both scatter plots. (From Hayes2020a)
• Figure 4: Top left: light curve of a stellar flare by Kepler and the result of a least-squares fit to the flare decay combined with the QPPs (red line). Top right: light curve after subtracting the flare decay trend with a decaying sinusoidal fit ( red line). Bottom left: autocorrelation function, with a fitted exponentially decaying sinusoid (red). Bottom right: wavelet spectrum of the top right plot and the global wavelet spectrum.(from Pugh2016a).
• Figure 5: Left: scatter plot of stellar effective temperature and QPP period. Right: scatter plot of stellar radius and QPP period. (from Pugh2016a