Quasi-Periodic Pulsations During the Impulsive and Decay Phases of an X-Class Flare

Abstract

Quasi-periodic pulsations (QPPs) are often observed in X-ray emission from solar flares. To date, it is unclear what their physical origins are. Here, we present a multi-instrument investigation of the nature of QPP during the impulsive and decay phases of the X1.0 flare of 2013 October 28. We focus on the character of the fine structure pulsations evident in the soft X-ray (SXR) time derivatives and compare this variability with structure across multiple wavelengths including hard X-ray and microwave emission. We find that during the impulsive phase of the flare, high correlations between pulsations in the thermal and non-thermal emissions are seen. A characteristic timescale of ∼20 s is observed in all channels and a second timescale of ∼55 s is observed in the non-thermal emissions. SXR pulsations are seen to persist into the decay phase of this flare, up to 20 minutes after the nonthermal emission has ceased. We find that these decay phase thermal pulsations have very small amplitude and show an increase in characteristic timescale from ∼40 s up to ∼70 s. We interpret the bursty nature of the coexisting multi-wavelength QPPs during the impulsive phase in terms of episodic particle acceleration and plasma heating. The persistent thermal decay phase QPPs are most likely connected with compressive magnetohydrodynamic processes in the post-flare loops such as the fast sausage mode or the vertical kink mode.

Seismology of contracting and expanding coronal loops using damping of kink oscillations by mode coupling

“…Nisticò et al (2013) observed an increase in the period of decayless kink oscillations in an expanding loop, and the magnitude of the increase was found to be consistent with the assumption of the magnetic field remaining constant. Hayes et al (2016) also related an increase in loop length during the decay phase of a flare to an increase in the timescale of quasi-periodic pulsations, although the increase in loop length was small compared with the increase in periods. The time-dependence of the period of oscillation used in Pascoe et al (2017a) and followed in this paper is based on a 3rd order polynomial to allow both increases and decreases during the observation.…”

Coronal loop seismology using damping of standing kink oscillations by mode coupling

“…Nisticò et al (2013) related the (linear) increase of the decayless kink oscillation period to the observed expansion of the loop. Russell et al (2015) examined the relationship between loop contraction and oscillation to changes in the magnetic environment produced by flares, while Hayes et al (2016) have recently measured an increase in loop length during the decay phase of a flare.…”

Detection and Interpretation of Long-lived X-Ray Quasi-periodic Pulsations in the X-class Solar Flare on 2013 May 14

“…Neupert (1968) had noted that the soft X-ray (SXR) light curve of many flares closely matched the time integral of the microwave light curve and this became the basis for what is now known as the Neupert Effect (Neupert 1968;Hudson 1991;Veronig et al 2005). Dennis & Zarro (1993) showed that this general relationship is more clearly evident if the time derivative of the SXR light curve is used since it tends to match the HXR light curve through the impulsive phase (see also Hayes et al 2016). Indeed, the GOES time derivative is now often used as a proxy for the HXR light curve if that is not available for a particular event, e.g.…”