Power-law Indices of EUV Intensity Power Spectrum in Flaring Coronal Active Regions

Abstract

Solar intensity power spectra are usually characterised by coloured noise, with the spectral energy following a segmented power-law function of frequency, $S(f)\propto f^{-\alpha }$, over different frequency ranges. Typically, the power-law index exceeds 1 in the low-frequency part (${\alpha }_{\mathrm{lf}}$) and is around 0 at high frequencies (${\alpha }_{\mathrm{hf}}$). This work investigates the spatial and temporal evolution of the power-law indices of coronal EUV intensity power spectra in flare-hosting active regions. The spatial distribution of the power-law index in the low-frequency domain (${\alpha }_{\mathrm{lf}}$) closely mirrors EUV intensity images, indicating that ${\alpha }_{\mathrm{lf}}$ can reveal the dynamics of coronal plasma structures. Temporally, ${\alpha }_{\mathrm{lf}}$ remains stable in quiescent active regions, but it exhibits significant variability before the flare onset. Motivated by this behaviour, we analysed 14 flare events, quantifying the temporal variation of the indices ${\alpha }_{\mathrm{lf}}$ and ${\alpha }_{\mathrm{hf}}$ as potential flare precursors. In all flare events considered, notable deviations of ${\alpha }_{\mathrm{lf}}$ beyond a defined threshold consistently occurred at the flare site within a few minutes before the flare. In some cases, the change in the value of ${\alpha }_{\mathrm{lf}}-{\alpha }_{\mathrm{hf}}$ was detected within 30--90\, minutes before the flare. This proof-of-concept study suggests that the temporal variation of the power-law indices in coronal EUV intensity power spectra could potentially serve as short-term precursors of solar flares, which needs to be validated on a larger flare sample.

19 pages, 9 figures, accepted for publication in ApJ

References in corpus (17)

• Power-law distributions in empirical data
• A Review of Vibration-Based Damage Detection in Civil Structures: From Traditional Methods to Machine Learning and Deep Learning Applications
• Kinetic Simulations of Magnetized Turbulence in Astrophysical Plasmas
• Flare-productive active regions
• Key Aspects of Coronal Heating
• Extension of the MURaM radiative MHD code for coronal simulations
• High-resolution observations of flare precursors in the low solar atmosphere
• A large-scale search for evidence of quasi-periodic pulsations in solar flares
• Probing the physics of the solar atmosphere with the Multi-slit Solar Explorer (MUSE): I. Coronal Heating
• Very Long-period Pulsations before the Onset of Solar Flares
• Coronal Fourier power spectra: implications for coronal seismology and coronal heating
• A blueprint of state-of-the-art techniques for detecting quasi-periodic pulsations in solar and stellar flares
• Observations of Dissipation of Slow Magneto-acoustic Waves in a Polar Coronal Hole
• Common origin of quasi-periodic pulsations in microwave and decimetric solar radio bursts
• A Correlation in the Waiting-time Distributions of Solar Flares
• Beyond small-scale transients: a closer look at the diffuse quiet solar corona
• The nature of small scale EUV solar brightenings investigated as impulsive heating of short loops in 1D hydrododynamics simulations