Localized Acceleration of Energetic Particles by a Weak Shock in the Solar Corona

Abstract

Globally propagating shocks in the solar corona have long been studied to quantify their involvement in the acceleration of energetic particles. However, this work has tended to focus on large events associated with strong solar flares and fast coronal mass ejections (CMEs), where the waves are sufficiently fast to easily accelerate particles to high energies. Here we present observations of particle acceleration associated with a global wave event which occurred on 2011 October 1. Using differential emission measure analysis, the global shock wave was found to be incredibly weak, with an Alfvén Mach number of ∼1.008–1.013. Despite this, spatially resolved type iii radio emission was observed by the Nançay RadioHeliograph at distinct locations near the shock front, suggesting localized acceleration of energetic electrons. Further investigation using magnetic field extrapolation identified a fan structure beneath a magnetic null located above the source active region, with the erupting CME contained within this topological feature. We propose that a reconfiguration of the coronal magnetic field driven by the erupting CME enabled the weak shock to accelerate particles along field lines initially contained within the fan and subsequently opening into the heliosphere, producing the observed type iii emission. These results suggest that even weak global shocks in the solar corona can accelerate energetic particles via reconfiguration of the surrounding magnetic field.

Observations of a Flare-ignited Broad Quasiperiodic Fast-propagating Wave Train

“…Since the measured intensity of the EUV images is a function of both the temperature and the density, the small percentage increase in temperature indicates that the measured EUV intensity variation is mainly due to the change of the plasma density rather than the temperature. Assume that the observed wave train propagated perpendicular to the direction of the magnetic field (see Vršnak et al 2002;Long et al 2021); this is reasonable, since the magnetic field in the quiet-Sun corona has a strong vertical component. The magnetosonic Mach number M ms can be calculated using…”

A Multi-Event Study of Early-Stage SEP Acceleration by CME-Driven Shocks—Sun to 1 AU

“…To characterize the kinematics of CBFs, we applied to the AIA observations the methodology of the Coronal Analysis of SHocks and Waves (CASHeW) framework (Kozarev et al, 2017), updated and implemented in SPREAdFAST. Our framework estimates the CBF kinematics in a similar way to Long et al (Long et al, 2021) and Downs et al (Downs et al, 2021), by following the leading edge of the front on consecutive images. In addition, we calculate the kinematics of the peak and back edge of the CBFs over time, which allows us to estimate their timedependent mean intensity and thickness.…”

“…Figure 4 shows parameter evolution along the individual shock-crossing field lines, for the May 11, 2011 event, between the solar surface and 10 R Sun . The panels show, in different colors, the shock-field angle θ BN , shock upstream magnetic field amplitude |B|, shock speed V shock , and the shock density jump ratio, r. Similarly to other authors, (Frassati et al, 2019;Frassati et al, 2020;Long et al, 2021), we employ DEM analysis to estimate the shock strength from AIA observations. We find that, while we use a different DEM model than these authors (Cheung et al, 2015), the general results are similar-we find weak coronal shocks.…”

A Multi-Event Study of Early-Stage SEP Acceleration by CME-Driven Shocks -- Sun to 1 AU

“…To characterize the kinematics of CBFs, we applied to the AIA observations the methodology of the Coronal Analysis of SHocks and Waves (CASHeW) framework [20], updated and implemented in SPREAdFAST. Our framework estimates the CBF kinematics in a similar way to Long et al [21] and Downs et al [22], by following the leading edge of the front on consecutive images. In addition, we calculate the kinematics of the peak and back edge of the CBFs over time, which allows us to estimate their time-dependent mean intensity and thickness.…”

“…Figure 4 shows parameter evolution along the individual shock-crossing field lines, for the May 11, 2011 event, between the solar surface and 10 R Sun . The panels show, in different colors, the shock-field angle θ BN , shock upstream magnetic field amplitude |B|, shock speed V shock , and the shock density jump ratio, r. Similarly to other authors, [34,35,21], we employ DEM analysis to estimate the shock strength from AIA observations. We find that, while we use a different DEM model than these authors [33], the general results are similar -we find weak coronal shocks.…”