Quasi-periodic pulsations in a solar flare with an unusual phase shift

Abstract

Two kinds of processes could occur during the flare decay phase: processes of energy release or processes of energy relaxation. Quasi-periodic pulsations (QPPs) of the broadband emission are a good tool for the verification of mechanisms. We aim to study the processes during the decay phase of the X-class solar flare SOL2014-03-29T17:48. The observations in X-ray, microwave, and extreme ultraviolet (EUV) bands are exploited to study the fine temporal, spatial, and spectral structures of the flare. The periods, amplitudes, and phases of both the fluxes and physical parameters (emission measure, temperature) are studied using standard methods of correlation, Fourier, and wavelet analyses. It is found that the source of the QPPs is associated with the uniform post-flare loop. The X-ray source is located at the top of the arcade. QPPs with the similar characteristic time scales of P ≈ 74-80 s are found in the X-ray (3-25 keV) and microwave (15.7 GHz) emissions. Besides, QPPs with the same period are found in the time profiles of both the temperature (T e ) and emission measure (E M). The QPPs in temperature and the QPPs in emission measure demonstrate anti-phase behavior. The analysis reveals the quasi-periodic process of energy relaxation, without any additional source of energy during the decay phase. The periods of the QPPs are in a good agreement with second harmonic of standing slow magneto-acoustic wave in the arcade which could be triggered by a Moreton wave initiated by the flare in the direct vicinity of the arcade.

Damping of slow magnetoacoustic oscillations by the misbalance between heating and cooling processes in the solar corona

“…A 2-min oscillation of the thermal component of the microwave emission of a solar flare has been interpreted in terms of the emission modulation by a standing slow wave. An 80 s oscillation of the X-ray and microwave emissions in a solar flare has been associated with second harmonic of standing slow wave in a flaring arcade (Kupriyanova et al 2019). The 8-30 min periodic pulsations of the soft X-ray emission generated in an active region before a flare could also be associated with standing slow waves (Tan et al 2016).…”

Quasi-Periodic Pulsations in Solar and Stellar Flares: A Review of Underpinning Physical Mechanisms and Their Predicted Observational Signatures

“…A heating pulse generates a strong pressure imbalance, which could travel along a confined coronal loop and bounce back and forth as slow mode magnetoacoustic wave, the modulation depth could reach over 20% of the emission intensity of the coronal loop. An interplay between the coronal heating and cooling processes was shown to be a new natural mechanism for formation of quasi-periodicity in initially broadband slow magnetoacoustic waves, resulting into the development of quasi-periodic slow wave trains(Zavershinskii et al, 2019, see also discussion of the acoustic thermal overstability in Section 2.3.3) Kupriyanova et al (2019). found correspondence between the Moreton wave and initiation of the QPPs in thermal and non-thermal emissions.…”

Analysis of Pulsation Spectra of Chromospheric Radiation from a Solar Flare SOL2015-10-01

“…As quasi-periodic pulsations in solar flares are damped oscillations of a quasi-harmonic or triangular shape against the background red noise [1,5], the red noise could result in false periods, and we should exclude them. That is why for selection of flare QPPs we used the technique proposed in the paper of [6].…”

“…There are two main classes of mechanisms explaining QPPs. The first one relates the observed pulsations to the direct impact of magnetohydrodynamic (MHD) waves, and the second mechanism is associated with a repetitive process of magnetic reconnection [1,3]. Often, the mechanisms of the two classes coexist and complement each other.…”