Letters of Intent received in 2019

LoI 2021-2121
Physics of relativistic jets on all scales

Date: 16 August 2021 to 27 August 2021
Location: IAU General Assembly, Busan, Korea, Rep of
Contact: Monica Orienti (monica.orienti@inaf.it)
Coordinating division: Division B Facilities, Technologies and Data Science
Other divisions: Division D High Energy Phenomena and Fundamental Physics
Division J Galaxies and Cosmology
Co-Chairs of SOC: Monica Orienti (INAF/IRA)
Bong Won Sohn (KASI)
Chair of LOC: None (None)



EHT results and launching jet region
Jet acceleration, propagation, collimation and dissipation
High resolution observations and polarization measurements
Relativistic jets in AGN and GRB
Jet ISM and IGM interactions
New surveys and the generation of new telescopes



Rationale (max 2 pages)
Requested duration: 2 days
Confirmed SOC members:
M. Giroletti; G. Giovannini; T. Jung; H. Falcke; D.M. Worrall; S. Jorstad; J. Gomez; M. Nakamura; R. Morganti; M. Boettcher; L.Nava; M. Petropoulou.
Possible Invited People (TBC):
K. Hada; A. Marscher; F. D’Ammando; E. Meyer; M. Lister; G. Ghirlanda; R. Wagner; M. Rioja; J. McKean; An Tao; T. Hovatta; C. Garcia Miro; S. Markoff; D. Gabuzda; A. Tchekhovskoy; Z.L. Uhm.

Scientific Rationale
Active Galactic Nuclei with relativistic jets are unique laboratories for studying the physics of matter and relativistic particles in extreme conditions. Jets powered by accretion onto a central SMBH are the most powerful and long-lived particle accelerators in the Universe.
Non-thermal processes operating in jets are responsible for multi-messenger emissions, such as broadband electromagnetic radiation and high-energy neutrinos that can be related to those of gamma-ray bursts (GRB) and gravitational-wave emitters.
MHD jet models find that part of the jet magnetic energy is used to accelerate the bulk flow to relativistic speeds, over a wide range of scales (from sub-pc to pc). However, the origin of the energy (SMBH spin, accretion disk….), the nature of the flow, and jet-dissipation properties are not yet well known. Tight constraints on physical models can be achieved by high-resolution observations of the innermost part of the jet structure in AGN through study of the brightness distribution, opening angle, and polarization. These results, in addition to outcomes of forthcoming observations of the SMBH shadow in nearby AGN will enable the study of the jet base and of the launching mechanisms.
The study of high redshift AGN may shed a light on merger processes and SMBH evolution. Furthermore, relativistic jets are thought to impact their host galaxies, and the study of the jet-ISM interplay that is often observed in young radio sources can provide crucial information on SMBH-galaxy feedback and on the evolution of the jet itself. Many jets propagate through their host galaxies and dissipate most energy on the scale of the intergalactic medium (IGM) instead.
Jets are involved in many transient phenomena like GRB and in the coalescence of neutron stars and stellar black holes. Results from high-resolution observations place constraints on the jet models and environment in these transient phenomena.
Recent and near-future developments in observing techniques in the electromagnetic band, such as e.g. the EHT telescope, mm-VLBI with ALMA, SKA-VLBI, large scale VLBI surveys, improved sensitivity high energy observations (e.g.CTA), and multi-messenger astronomy provide a step forward in our understanding of the physics of relativistic jets.