Particle-in-cell simulations of relativistic Weibel-mediated shocks propagating into inhomogeneous media

Sara Tomita, Yutaka Ohira

Research output: Contribution to journalConference articlepeer-review


The cosmic rays above the second knee energy (1017 eV) are expected to be accelerated by extragalactic sources, such as relativistic jets of gamma-ray bursts (GRBs) and active galactic nucleus. The relativistic jets drive a relativistic Weibel mediated shock if the upstream magnetic field is sufficiently weak. External shocks of GRBs can accelerate CRs to 1017 eV if the magnetic field generated by the Weibel instability around the shock front do not decay in the far downstream region. However, particle-in-cell (PIC) simulations show that the magnetic fields decay rapidly for the Weibel mediated shocks in a uniform plasma. In reality, there are density fluctuations in interstellar or circumstellar medium. In this study, we preformed two-dimensional PIC simulations of relativistic shocks propagating to inhomogeneous electron-positron plasma. We found that the downstream magnetic field keeps a higher values and larger scales than those for the uniform case. Furthermore, sound and entropy waves are excited by interaction of the upstream density fluctuations with the shock, which would accelerate particles to a higher energy by the second-order acceleration. Therefore, the upstream inhomogeneity plays a crucial role in the CR acceleration and generation of the magnetic field in the far downstream region.

Original languageEnglish
JournalProceedings of Science
Publication statusPublished - 2019
Externally publishedYes
Event36th International Cosmic Ray Conference, ICRC 2019 - Madison, United States
Duration: 2019 Jul 242019 Aug 1

ASJC Scopus subject areas

  • General


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