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Three-dimensional kinetic simulations of "ABC fields"

Cosmic sources of high-energy gamma-ray radiation, including blazars and pulsars, are characterized by the presence of extreme plasma, the energy of which is dominated by the magnetic component. In such plasmas, complicated physical processes take place, e.g., magnetic reconnection, that lead to dissipation of magnetic energy, particle acceleration and gamma-ray emission. These processes can be to certain degree investigated by means of numerical simulations, in particular by using the kinetic algorithm called particle-in-cell. Such numerical simulations employ various initial configurations, and one of the recently proposed options are so-called "ABC fields". In the ABC fields, each component of magnetic field can be described as a sinusoidal standing wave extending over the entire simulation domain. It is a highly idealized periodic configuration that leads to very interesting effects, in particular it allows to investigate the formation of kinetically thin current layers, which are the sites of magnetic reconnection, as well as the associated particle acceleration and gamma-ray emission. All these processes are simultaneous and very dynamic, and hence numerical simulations are inevitable for their detailed characterization.


Dr. Krzysztof Nalewajko from NCAC PAS obtained the first three-dimensional kinetic numerical simulations of ABC fields, using the largest Polish supercomputer Prometheus at ACK Cyfronet AGH in Cracow, as well as the supercomputer Mira at ALCF ANL in Argonne, USA. These simulations extend the previous two-dimensional simulations obtained in collaboration with the group of Prof. Roger Blandford at the Stanford University, USA, the results of which were published in 2016. The new three-dimensional simulations confirm most of the key results of the two-dimensional simulations, at the same time showing some important differences, e.g., the interaction of pairs of current layers.


The article titled "Three-dimensional kinetic simulations of relativistic magnetostatic equilibria" has been published in the journal Monthly Notices of the Royal Astronomical Society. Animations of selected simulation results can be found on author's website.


The attached figures present visualizations of the results of one simulation at the moment of a merger between pairs of current layers. The first figure shows the three-dimensional distribution of the magnetic field strength (white - weak field, dark green - strong field). The second figure shows the two-dimensional distribution of magnetic fields, as well as regions where electric field is parallel to the magnetic field (pink). The third figure shows the two-dimensional distribution of electric currents, with main current layers indicated as dark green patches, while regions of high mean particle energy are indicated with orange contours.


This project is supported by the Polish National Science Center with the SONATA BIS grant number 2015/18/E/ST9/00580.