Particle Acceleration and Heating by the Turbulence in the Interstellar / Intracluster Gas and Nonequilibrium Radiation due to Quasi-Thermal Electrons

2018 Fiscal Year Final Research Report

• Project/Area Number: 15K05024
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Astronomy
• Research Institution: Tokyo Metropolitan University
• Principal Investigator: Masai Kuniaki 首都大学東京, 理学研究科, 教授 (80181626)
• Project Period (FY): 2015-04-01 – 2019-03-31
• Keywords: 乱流 / 2次Fermi加速 / Fokker-Planck方程式 / 準熱的粒子 / 銀河団 / 電波ハロー / 冷却コア / 非平衡放射

Outline of Final Research Achievements

Particle acceleration by the turbulence is investigated with a Fokker-Planck code which calculates the advection and diffusion in the momentum space, and applied to the intracluster gas of galaxy clusters. We have developed the code considering higher-order terms due to small-angle scattering into the advection and/or diffusion coefficients, intending to describe heating as well as acceleration. For the turbulence of 500 km/s decaying to less than 170 km/s in 1 Gyr through inverse cascade, it is found that the cool core of a cluster is heated to about twice the temperature before, and accelerated electrons emit synchrotron radio as intense as observed from radio halos. Also found is that while the radio emission lasts for a long time, hard X-ray emission declines quickly after the turbulence decay.

Free Research Field

宇宙物理学

Academic Significance and Societal Importance of the Research Achievements

乱流による加速は，衝撃波加速と相補的に，宇宙の高エネルギー粒子加速において重要な物理過程であり，衝撃波に比べて加速時間がかかるが硬いスペクトルをつくれるという特徴がある．銀河団ガスでは，衝撃波と同様に，乱流による加熱が期待されるが，分布関数で実証した例は少なく，あっても拡散係数に変更を加えるものであった．本研究では，拡散係数を高次の項まで考慮することで加速・加熱を整合的に示すことができた．インジェクション項を持たない2次Fermi加速過程をより適切に扱う一つの方法を示したと言え，広く，宇宙の高エネルギー粒子や星間・銀河間ガスの加熱の理解に寄与するものと考える．