Why Blazar Jets Shine: Radiative Relativistic Reconnection and the Minijet Model

点击翻译按钮获取中文摘要

Blazars are a subset of active galactic nuclei, which are highly energetic cores of galaxies, singled out by the fact that their jets of material, flowing out at speeds approaching that of light, just happen to be arranged so as to point towards us. As such, blazars provide a direct view of how energy is radiated away and degraded in and around fast moving plasmas. Unfortunately, the current explanations have proven inadequate. This research team has introduced a new model that looks very promising in initial, approximate, studies. This project will use new computational techniques to simulate the motions of large amounts of high-speed plasma, to study the problems in sufficient detail to distinguish between the possible alternatives by comparing with astronomical observations. The research tool developed for this work will be packaged for others to use in many areas of plasma science.Blazars are the primary sources of persistent extragalactic gamma-ray radiation detected by ground- and space-based observatories. They provide a direct view of dissipation and radiative processes in relativistic collisionless plasmas. Recent observations of rapid intense flares imply that the emitting regions are very compact and propagate with much higher Lorentz factors than the bulk jet values deduced from radio observations. A semi-analytical model using localized, relativistic sub-flows, called minijets, has reproduced the main features of flaring blazars, but is based on crude approximations. This project will use a new, fully radiative Particle-in-Cell (PIC) code to study collisionless reconnection in relativistic plasmas, including the effects that plasma magnetization, the strength of the magnetic guide field, and the plasma composition, can have on bulk plasma motions, particle acceleration, and radiative signatures. Simulated time-dependent spectra will be compared to existing data. The puzzling gamma-ray flares from the Crab Nebula cannot be due to shock acceleration or any other magnetohydrodynamic process, and this research team's comprehensive model is the first compelling case for reconnection as the main dissipation mechanism in a distant astrophysical system. The present work will study the bulk kinematics of relativistic reconnection outflows, the effects of plasma composition on reconnection outflows, and radiation processes in these self-same outflows. These will be the first kinetic simulations to model relativistic reconnection in an electron-ion plasma, and among the first to treat radiative losses self-consistently.The powerful research tool used here will be made freely available, with all necessary documentation, test problems, diagnostic tools, and sample scripts. The study itself applies widely not only to other astrophysical systems such as pulsar wind nebulae, gamma-ray bursts, and accretion disk coronae, but also to space physics applications and laboratory plasmas. One postdoctoral researcher will be supported, trained, and mentored in high-performance computing and the use of simulations.