Probing Accretion and Relativistic Jet Physics with the Dynamic Multimessenger Universe

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The physical processes by which most matter accumulates onto astrophysical objects, accretion, are intimately tied to a second set of physical processes, outflows. Astrophysicists call the most highly focused outflows "jets." Most observed jets in our Universe involve processes that accelerate populations of both individual electrons and the bulk outflow of particles to relativistic speeds (i.e., speeds near that of light). Accretion and relativistic jets lead to bright electromagnetic signals. Accretion is often bright at X--ray wavelengths. And relativistic jets are bright at near--infrared through radio wavelengths. Sources undergoing outbursts of accretion and astrophysical jets serve as beacons for both extreme-detail studies in our Galaxy and en masse, lesser-detail studies across the observable Universe. Despite knowing of such sources for more than 50 years, we still cannot answer: "What process or processes accelerate jets?; What differentiates how different types of jets are launched?; and What is the precise role of these sources in galaxy formation?". My long-term goal is to answer these critical questions that apply to objects ranging from individual stars as they are being born to black holes billions of times as massive as the Sun sitting at the centre of galaxies. Given the broad gamut of source types, understanding the connection between accretion and jets is a high--priority goal in astrophysics. Astrophysicists have recently linked astrophysical jets with the first extragalactic events that we can study with non-electromagnetic signals (e.g., signals from high-speed particles, like neutrinos, and gravitational waves). To probe the physics connecting accretion and jets and better understand multi-messenger sources, astrophysicists must measure the properties of jets and, where possible, tie these to properties of accretion. My short-term research program will exploit multiple avenues of time--domain observations across the electromagnetic spectrum to provide these data and theoretical interpretations. I will combine: 1) nearly--simultaneous timing and imaging observations across the electromagnetic spectrum of actively accreting stellar-mass black holes and neutron stars using sets of international facilities (including National Research Council of Canada or Canadian Space Agency co-supported facilities); 2) surveys that reveal the radio and X--ray properties of large numbers of astrophysical objects that will enable my group to identify the nature of these objects, constrain the properties of entire populations, and motivate detailed followup of the most extreme objects; and 3) lead the Canadian multi--messenger astrophysics community's radio response to neutrino and gravitational wave events. I will train 1 Postdoctoral Fellow, 3 Ph.D. students, 4 M.Sc students, and 5 undergraduate students. I will also host 5 South African graduate students for three-month visits to Canada for scientific training.