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tokens: of the potential field energy E p ( t ) (thick curve with diamonds) and the free energy E f ( t ) (thin curve with crosses), both normalized to their maximum, the loop elimination ratio q e , and cross-correlation coefficient CCC. Note that the potential field energy and the free energy are uncorrelated. 5. Interpretation and Discussion 5.1. Instrumental Oscillatory Effects As these observations report for the first time oscillations in the free (magnetic) energy of solar flares, we discuss first possible effects of instrumental origin. The range of observed oscillations (in 11 flare events) cover the range of P ≈ 10–22 minutes and have a mean and standard deviation of As the SDO spacecraft is positioned in the Lagrangian point L1, there are no eclipsing time intervals of the spacecraft orbit that could modulate the observed flux. Because the Sun is rotating, any tracking of a particular heliographic position of a solar flare or an active region needs to be interpolated between two pixels, which could possibly introduce a pixel-step modulation. We estimate the timescale of a pixel shift based on the synodic solar rotation rate,which amounts for a synodic rotation time of P syn = 27.27 days, an HMI pixel size of Δ x pix = 05, and an average solar radius of R ⊙ ≈ 960′′, to a time interval of Δ t pix = 3.2 minutes for HMI, or Δ t pix = 3.9 minutes for AIA pixels. The beat frequency between the two instruments amounts to a timescale ofAlthough the beat frequency is close to the frequency of the observed mean oscillation period (Equation ( 17 )), subpixel variations of the sensitivity (or modulation transfer function) of AIA are unlikely to explain the observed oscillations, as the width of the point-spread function (PSF) is substantially wider (15) than the pixel size (06) (Boerner et al. 2012 ; Grigis et al. 2012 ; Lemen et al. 2012 ). The PSF may also imply a slight subpixel variation of the sensitivity of CCD pixels (between the pixel center and pixel edge). We calculated this variation by pixel-wise superposition of PSFs, and found an interpixel variation of ≲3%. Moreover, the rms variation in the AIA flat field is found to be of order 2% (Boerner et al. 2012 ). The PSF was also measured during a lunar transit, finding that the PSF of AIA/ SDO is better by a factor of two than the EUV telescope on board TRACE (Poduval et al. 2013 ). In summary, no instrumental effect is known from AIA or HMI that could modulate the observed free energy evolution E f ( t ) with periods of P ≈ 10–20 minutes (J. Lemen et al. 2020, private communication). Incidentally, we did choose a cadence of 3 minutes for the AIA images with the VCA4-NLFFF code, while a cadence of 12 minutes is available from the W-NLFFF code using HMI data (Aschwanden 2019c ). The cadence of 12 minutes is close to the mean observed period of P obs = 15.1 ± 3.9 minutes, and thus the observed oscillations are fully resolved with the 3-minute cadence of the VCA4-NLFFF code only, while they