Numerical simulation of superhalo electrons generated by magnetic reconnection in the solar wind source region

• Published in: Research in astronomy and astrophysics 2015-03, Vol.15 (3), p.348-362
• Main Authors: Yang, Li-Ping, Wang, Ling-Hua, He, Jian-Sen, Tu, Chuan-Yi, Zhang, Shao-Hua, Zhang, Lei, Feng, Xue-Shang
• Format: Article
• Language: English
• Subjects: Acceleration; Computer simulation; Direct current; Electric fields; Electrical resistivity; Magnetic fields; Magnetohydrodynamics; Mathematical models; Solar wind; 动力学性能; 太阳风; 幂律分布; 数值模拟; 源区; 电子数; 磁重联; 粒子模拟
• ISSN: 1674-4527; 2397-6209
• DOI: 10.1088/1674-4527/15/3/005

Superhalo electrons appear to be continuously present in the interplane- tary medium, even during very quiet times, with a power-law spectrum at energies above ～2 keV. Here we numerically investigate the generation of superhalo electrons by magnetic reconnection in the solar wind source region, using magnetohydrody- namics and test particle simulations for both single X-line reconnection and multiple X-line reconnection. We find that the direct current electric field, produced in the mag- netic reconnection region, can accelerate electrons from an initial thermal energy of T ～105 K up to hundreds of keV. After acceleration, some of the accelerated elec- trons, together with the nascent solar wind flow driven by the reconnection, propagate upwards along the newly-opened magnetic field lines into interplanetary space, while the rest move downwards into the lower atmosphere. Similar to the observed superhalo electrons at 1 AU, the flux of upward-traveling accelerated electrons versus energy dis- plays a power-law distribution at ～ 2-100 keV, f（E）～ E^-δ, with a 6 of ～1.5 - 2.4. For single （multiple） X-line reconnection, the spectrum becomes harder （softer） as the anomalous resistivity parameter a （uniform resistivity η） increases. These modeling results suggest that the acceleration in the solar wind source region may contribute to superhalo electrons.