Session:- Relativistic jets and particle acceleration.2
Theoretical and observational studies of astrophysical black holes have been in rapid development in recent decades. This conference will present major breakthroughs and key remaining questions concerning our fundamental understanding of astrophysical black holes, such as the formation and collimation of relativistic jets, the accretion and growth of black holes, the measurement of black hole spin, the merger of black holes, the first images of black hole shadow, the particle acceleration mechanisms and transient phenomena around black holes, and the feedback from massive black holes to galaxies.
◎Black holes as cosmic accelerators
The origin of ultra high energy cosmic rays remains a mystery. It represents the challenge of finding the nature of the most powerful particle accelerators in the Universe, which exhibit collisions with center of mass energies about 100 times those attainable at the LHC. During their acceleration process, they produce high energy gamma-rays and neutrinos. These secondary messengers reveal clues about the extreme environments around stellar or supermassive black holes. The speaker will present models of the powerful cosmic engines associated with black holes and review the possible sources candidates in light of some recent developments in Multimessenger Astrophysics.
講者：Dr Noemie Globus
◎Particle acceleration in AGN jets
Jets of active galactic nuclei are observed from less than parsec scale to mega-parsec scale. They are powerful particle accelerators shining across the electromagnetic spectrum. In this talk,
(1) The speaker will mainly present their analytical and numerical works on shear acceleration. Recent observations indicate a synchrotron origin of X-ray emission in kpc-scale, which requires in-situ acceleration of electrons up to near PeV energies. They found an exact solution of the steady-state Fokker-Planck equation for shear acceleration. This produces a power-law spectrum with an exponential-like cut-off for particles, which can naturally explain the multi-wavelength observations of the kpc-scale jets, such as Centaurus A and 3C 273. Their relativistic MHD simulations and test-particle simulations validate the assumptions of our analytical theory and show that protons can be accelerated to the Hillas limit via shear acceleration.
(2) The speaker will also briefly discuss the particle acceleration mechanisms in sub-pc scale jets, especially for the limb-brightened structures.
講者：Dr Jieshuang Wang
◎Extreme particle acceleration at AGN jet termination shocks
Extragalactic plasma jets are some of the few astrophysical environments able to confine ultra-high energy cosmic rays, but whether they are capable of accelerating these particles is unknown. In this work, the research team revisits particle acceleration at relativistic magnetized shocks beyond the local uniform field approximation, by considering the global transverse structure of the jet. Using large two-dimensional particle-in-cell simulations of a relativistic electron-ion plasma jet, they show that the termination shock forming at the interface with the ambient medium accelerates particles up to the confinement limit. The radial structure of the jet magnetic field leads to a relativistic velocity shear that excites a von Kármán vortex street in the downstream medium trailing behind an over-pressured bubble filled with cosmic rays. Particles are efficiently accelerated at each crossing of the shear flow boundary layers. These findings support that extragalactic plasma jets may be capable of producing ultra-high energy cosmic rays. This extreme particle acceleration mechanism may also apply to microquasar jets.
講者：Prof. GIACINTI, Gwenael (Tsung-Dao Lee Institute & Shanghai Jiao Tong University)
地點：香港大學 百週年校園 CPD 3.04 Centennial Campus