Studies of Relativistic Jets in Active Galactic Nuclei with SKA

Abstract

Relativistic jets in active galactic nuclei (AGN) are among the most powerful astrophysical objects discovered to date. Indeed, jetted AGN studies have been considered a prominent science case for SKA, and were included in several different chapters of the previous SKA Science Book (Carilli & Rawlings 2004). Most of the fundamental questions about the physics of relativistic jets still remain unanswered, and await high-sensitivity radio instruments such as SKA to solve them. These questions will be addressed specially through analysis of the massive data sets arising from the deep, all-sky surveys (both total and polarimetric flux) from SKA1. Wide-field verylong-baseline-interferometric survey observations involving SKA1 will serve as a unique tool for distinguishing between extragalactic relativistic jets and star forming galaxies via brightness temperature measurements. Subsequent SKA1 studies of relativistic jets at different resolutions will allow for unprecedented cosmological studies of AGN jets up to the epoch of re-ionization, enabling detailed characterization of the jet composition, magnetic field, particle populations, and plasma properties on all scales. SKA will enable us to study the dependence of jet power and star formation on other properties of the AGN system. SKA1 will enable such studies for large samples of jets, while VLBI observations involving SKA1 will provide the sensitivity for pc-scale imaging, and SKA2 (with its extraordinary sensitivity and dynamic range) will allow us for the first time to resolve and model the weakest radio structures in the most powerful radio-loud AGN.

The connection between radio and high energy emission in black hole powered systems in the SKA era

“…Since blazars are continuum emission sources with flat spectrum, the choice of bands can reasonably be adjusted; however, it would be highly desirable to keep the highest frequency bands (4.6-13.8 GHz for SKA1-MID, and possibly 1.5-4.0 GHz for SKA1-SUR), where there is less contamination from steep spectrum sources and de-polarization effects are less severe. Indeed, polarization has not been discussed so far in this Chapter but it will be a very important probe to the physics (see also the Chapter by Agudo et al 2015). The full band and the longest baselines provided by SKA2 will provide further critical information (5.3).…”

“…Indeed, understanding the blazar phenomenon inevitably requires a characterization of the physical properties of relativistic jets, which are the subject of other Chapters of this book (e.g. Agudo et al, 2015). In the present Chapter, in particular, we plan to highlight how the SKA project will shed light on the properties of gamma-ray sources as a population, starting from ongoing and incipient works with pathfinders and precursors, continuing with the SKA itself in its phase 1 and ultimately with the full sensitivity and frequency range that will be available in phase 2.…”

“…This Chapter is organized as follows: in Section 2, we present an outline of the current and planned HE and VHE surveys; in Section 3, we review the state of the art about the connection between radio and gammaray emission (3.1) and the search for unidentified gamma-ray source (UGS) counterparts (3.2); a sample ongoing topics are presented in Section 4; in Section 5, we finally deal with the prospects for SKA in these areas. Further topics are discussed in other Chapters of this book (Agudo et al, 2015;Bignall et al, 2015;Corbel et al, 2015;Donnarumma et al, 2015;Paragi et al, 2015;Turriziani et al, 2015), as the connection between radio and high energy emission in black hole powered system (both stellar and super massive) is of great interest and has implications on many other areas of astrophysics.…”

SKA Deep Polarization and Cosmic Magnetism

“…A deep full-polarimetric SKA1-MID survey on Bands 2 and 3 reaching a sensitivity of 75 nJy/beam will have the ability to attack the long standing problem of the composition of AGN jets (i.e. the electron-proton content), and their plasma acceleration from large samples suited for statistical studies for the first time, see Agudo et al (2015). For that, it is essential to have available a circular polarization purity at least ∼ 0.01 %, since AGN typically show circular polarization moduli in the range 0.1 − 1 % at centimetre radio wavelengths.…”

Very Long Baseline Interferometry with the SKA

“…Very long baseline interferometry with the SKA (hereafter SKA-VLBI) will provide very sensitive, milliarcsecond (mas) resolution imaging that is important, for example, to study active galactic nuclei (AGN) down to very low luminosities, to understand the detailed physics of jet formation and its coupling to the accretion process, as well as the growth of the first generation of massive black holes in the universe (Agudo et al 2015), and their role in regulating star formation (a.k.a. feedback processes, see Prandoni & Seymour 2015;Morganti et al 2015).…”