Relation Between the Coronal Mass Ejection Acceleration and the Non-Thermal Flare Characteristics

Abstract

We investigate the relationship between the main acceleration phase of coronal mass ejections (CMEs) and the particle acceleration in the associated flares as evidenced in Reuven Ramaty High Energy Solar Spectroscopic Imager non-thermal X-rays for a set of 37 impulsive flare-CME events. Both the CME peak velocity and peak acceleration yield distinct correlations with various parameters characterizing the flare-accelerated electron spectra. The highest correlation coefficient is obtained for the relation of the CME peak velocity and the total energy in accelerated electrons (c = 0.85), supporting the idea that the acceleration of the CME and the particle acceleration in the associated flare draw their energy from a common source, probably magnetic reconnection in the current sheet behind the erupting structure. In general, the CME peak velocity shows somewhat higher correlations with the non-thermal flare parameters than the CME peak acceleration, except for the spectral index of the accelerated electron spectrum, which yields a higher correlation with the CME peak acceleration (c ≈ −0.6), indicating that the hardness of the flare-accelerated electron spectrum is tightly coupled to the impulsive acceleration process of the rising CME structure. We also obtained high correlations between the CME initiation height h 0 and the non-thermal flare parameters, with the highest correlation of h 0 to the spectral index δ of flare-accelerated electrons (c ≈ 0.8). This means that CMEs erupting at low coronal heights, i.e., in regions of stronger magnetic fields, are accompanied by flares that are more efficient at accelerating electrons to high energies. In the majority of events (∼80%), the non-thermal flare emission starts after the CME acceleration, on average delayed by ≈6 minutes, in line with the standard flare model where the rising flux rope stretches the field lines underneath until magnetic reconnection sets in. We find that the current sheet length at the onset of magnetic reconnection is 21 ± 7 Mm. The flare hard X-ray peaks are well synchronized with the peak of the CME acceleration profile, and in 75% of the cases they occur within ±5 minutes. Our findings provide strong evidence for the tight coupling between the CME dynamics and the particle acceleration in the associated flare in impulsive events, with the total energy in accelerated electrons being closely correlated with the peak velocity (and thus the kinetic energy) of the CME, whereas the number of electrons accelerated to high energies is decisively related to the CME peak acceleration and the height of the pre-eruptive structure.

How Does Magnetic Reconnection Drive the Early-stage Evolution of Coronal Mass Ejections?

“…Thus the distribution is slightly asymmetric with a few more events where CME acceleration appears to rise earlier than the rise of flare reconnection. This asymmetry is consistent with but less remarkable than that using the CME acceleration and the hard X-ray emission reported by Berkebile-Stoiser et al (2012). Fig.…”

Solar eruptions: The CME‐flare relationship

“…In this respect it should be stressed that detailed inspection of graphs presented in these two studies again discloses that the acceleration starts before the flare impulsive phase, represented now directly by the HXR burst, and ends after it. Finally, Berkebile-Stoiser et al (2012) showed that the hardness of the flare HXR spectra is distinctly correlated with the CME acceleration. In most of the events, the CME acceleration started before the flare.…”

Large-scale Globally Propagating Coronal Waves

“…However, it has been shown that the acceleration profile of CMEs tends to peak during this period, too (cf. Zhang et al, 2001;Maričić et al, 2007;Temmer et al, 2008;Berkebile-Stoiser et al, 2012). Since coronal waves are highly associated with CMEs too (Section 5.2), timing alone cannot be used to make a distinction between a flare-related and a CME-related wave launch mechanism.…”