TY - JOUR
T1 - Electron Acceleration and Heating during Magnetic Reconnection in the Earth's Quasi-parallel Bow Shock
AU - Bessho, Naoki
AU - Chen, Li-Jen
AU - Hesse, Michael
AU - Ng, Jonathan
AU - Wilson III, L. B.
AU - Stawarz, Julia
N1 - Funding information: This work was supported by NASA grants 80NSSC20K1312 and 80NSSC18K1369, the NASA MMS project, and the Royal Society University Research Fellowship URF\R1\201286. Some of the work was supported by the Geospace Environment Modeling Focus Group "Particle Heating and Thermalization in Collisionless Shocks in the Magnetospheric multiscale mission (MMS) Era" led by L.B. Wilson III. PIC simulations were performed on Pleiades at the NASA Advanced Supercomputing, and the simulation data are available upon request from the authors.
PY - 2023/9/1
Y1 - 2023/9/1
N2 - We perform a 2.5-dimensional particle-in-cell simulation of a quasi-parallel shock, using parameters for the Earth’s bow shock, to examine electron acceleration and heating due to magnetic reconnection. The shock transition region evolves from the ion-coupled reconnection dominant stage to the electron-only reconnection dominant stage, as time elapses. The electron temperature enhances locally in each reconnection site, and ion-scale magnetic islands generated by ion-coupled reconnection show the most significant enhancement of the electron temperature. The electron energy spectrum shows a power law, with a power-law index around 6. We perform electron trajectory tracing to understand how they are energized. Some electrons interact with multiple electron-only reconnection sties, and Fermi acceleration occurs during multiple reflections. Electrons trapped in ion-scale magnetic islands can be accelerated in another mechanism. Islands move in the shock transition region, and electrons can obtain larger energy from the in-plane electric field than the electric potential in those islands. These newly found energization mechanisms in magnetic islands in the shock can accelerate electrons to energies larger than the achievable energies by the conventional energization due to the parallel electric field and shock drift acceleration. This study based on the selected particle analysis indicates that the maximum energy in the nonthermal electrons is achieved through acceleration in ion-scale islands, and electron-only reconnection accounts for no more than half of the maximum energy, as the lifetime of sub-ion-scale islands produced by electron-only reconnection is several times shorter than that of ion-scale islands.
AB - We perform a 2.5-dimensional particle-in-cell simulation of a quasi-parallel shock, using parameters for the Earth’s bow shock, to examine electron acceleration and heating due to magnetic reconnection. The shock transition region evolves from the ion-coupled reconnection dominant stage to the electron-only reconnection dominant stage, as time elapses. The electron temperature enhances locally in each reconnection site, and ion-scale magnetic islands generated by ion-coupled reconnection show the most significant enhancement of the electron temperature. The electron energy spectrum shows a power law, with a power-law index around 6. We perform electron trajectory tracing to understand how they are energized. Some electrons interact with multiple electron-only reconnection sties, and Fermi acceleration occurs during multiple reflections. Electrons trapped in ion-scale magnetic islands can be accelerated in another mechanism. Islands move in the shock transition region, and electrons can obtain larger energy from the in-plane electric field than the electric potential in those islands. These newly found energization mechanisms in magnetic islands in the shock can accelerate electrons to energies larger than the achievable energies by the conventional energization due to the parallel electric field and shock drift acceleration. This study based on the selected particle analysis indicates that the maximum energy in the nonthermal electrons is achieved through acceleration in ion-scale islands, and electron-only reconnection accounts for no more than half of the maximum energy, as the lifetime of sub-ion-scale islands produced by electron-only reconnection is several times shorter than that of ion-scale islands.
KW - Planetary bow shocks
KW - Interplanetary particle acceleration
KW - Solar magnetic reconnection
U2 - 10.3847/1538-4357/ace321
DO - 10.3847/1538-4357/ace321
M3 - Article
SN - 0004-637X
VL - 954
SP - 1
EP - 30
JO - The Astrophysical Journal
JF - The Astrophysical Journal
IS - 1
M1 - 25
ER -