arXiv subjects

Eoin P. Carley

Publications and source records attributed to Eoin P. Carley.

21 records · Page 2Linked to original sources

arXiv2014

Quasiperiodic acceleration of electrons by a plasmoid-driven shock in the solar atmosphere

Cosmic rays and solar energetic particles may be accelerated to relativistic energies by shock waves in astrophysical plasmas. On the Sun, shocks and particle acceleration are often associated with the eruption of magnetized plasmoids, called coronal mass ejections (CMEs). However, the physical relationship between CMEs and shock particle acceleration is not well understood. Here, we use extreme ultraviolet, radio and white-light imaging of a solar eruptive event on 22 September 2011 to show that a CME-induced shock (Alfvén Mach number 2.4$^{+0.7}_{-0.8}$) was coincident with a coronal wave and an intense metric radio burst generated by intermittent acceleration of electrons to kinetic energies of 2-46 keV (0.1-0.4 c). Our observations show that plasmoid-driven quasi-perpendicular shocks are capable of producing quasi-periodic acceleration of electrons, an effect consistent with a turbulent or rippled plasma shock surface.

astro-ph.SR↗

arXiv2014

The formation heights of coronal shocks from 2D density and Alfvén speed maps

Super-Alfvénic shock waves associated with coronal mass ejections (CMEs) can produce radio emission known as Type II bursts. In the absence of direct imaging, accurate estimates of coronal electron densities, magnetic field strengths and Alfvén speeds are required in order to calculate the kinematics of shocks. To date, 1D radial models have been used, but these are not appropriate for shocks propagating in non-radial directions. Here, we study a coronal shock wave associated with a CME and Type II radio burst using 2D electron density and Alfvén speed maps to determine the locations that shocks are excited as the CME expands through the corona. Coronal density maps were obtained from emission measures derived from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) and polarized brightness measurements from the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO). Alfvén speed maps were calculated using these density maps and magnetic field extrapolations from the Helioseismic and Magnetic Imager (SDO/HMI). The computed density and Alfvén speed maps were then used to calculate the shock kinematics in non-radial directions. Using the kinematics of the Type II burst and associated shock, we find our observations to be consistent with the formation of a shock located at the CME flanks where the Alfvén speed has a local minimum. 1D density models are not appropriate for shocks that propagate non-radially along the flanks of a CME. Rather, the 2D density, magnetic field and Alfvén speed maps described here give a more accurate method for determining the fundamental properties of shocks and their relation to CMEs.

astro-ph.SR↗

arXiv2012

Coronal Mass Ejection Mass, Energy, and Force Estimates Using STEREO

Understanding coronal mass ejection (CME) energetics and dynamics has been a long-standing problem, and although previous observational estimates have been made, such studies have been hindered by large uncertainties in CME mass. Here, the two vantage points of the Solar Terrestrial Relations Observatory (STEREO) COR1 and COR2 coronagraphs were used to accurately estimate the mass of the 2008 December 12 CME. Acceleration estimates derived from the position of the CME front in 3-D were combined with the mass estimates to calculate the magnitude of the kinetic energy and driving force at different stages of the CME evolution. The CME asymptotically approaches a mass of 3.4\pm1.0x10^15 g beyond ~10 R_sun. The kinetic energy shows an initial rise towards 6.3\pm3.7x10^29 erg at ~3 R_sun, beyond which it rises steadily to 4.2\pm2.5x10^30 erg at ~18 R_sun. The dynamics are described by an early phase of strong acceleration, dominated by a force of peak magnitude of 3.4\pm2.2x10^14N at ~3 R_sun, after which a force of 3.8\pm5.4x10^13 N takes affect between ~7-18 R_sun. These results are consistent with magnetic (Lorentz) forces acting at heliocentric distances of <7 R_sun, while solar wind drag forces dominate at larger distances (>7 R_sun).

astro-ph.SR↗