Relativistic jets from accreting black holes: are they baryonic or leptonic?

Relativistic outflows are often associated with accreting into compact objects, in particular, black holes. These outflows are collimated, in the form of jets. How these jets are launched is an resolved issue that challenge astrophysics for decades. Little is also know what exactly are in the jets. In most studies the jets are modeled as magneto-hydrodynamical flows of electron-proton plasmas. However, there are also studies which argue that relativistic jets from accreting black holes are leptonic, i.e. they are electron-positron plasmas flows. Regardless of whether the jets are baryonic or leptonic, the high-energy contents in the jet material and the violent phenomena associated withe relativistic flows in jets, such as shocks and entrainment of the jets with the clumpy ambient material would give rise to electron-positron pair production. These pairs would imprint observational signatures. These signatures would provide useful diagnostics of the relativistic flow dynamics and the physical conditions in the jets, as well as how the jets are interacting with their environments. Pair production in relativistic jets has not been fully explored, especially in the context of jet-environment interaction and in the hybrid baryonic/leptonic settings.

In the project, the student will develop structured jet models in which pair-production occur and calculate the associated radiative processes. It is a theoretical project, which involves phenomenological modeling, analytical calculations and numerical computation. It aims to derive predictions that can be tested by current or future X-ray/gamma-ray/radio observations and to provide useful working models that are applicable in other branches of astrophysics, e.g. astro-particle physics involving UHE cosmic rays and neutrinos.