Dr. Prasun Dhang

Jets are observed in the low/hard state of a transient black hole binary (BHB). Jet production is proposed to be connected to the presence of a radiatively inefficient accretion flow (RIAF) and large-scale magnetic fields close to the accreting black hole (BH). However, source of the large-scale fields is not quite obvious. Two plausible sources of the large-scale magnetic fields are: i) in-situ generation of the magnetic field by a dynamo action and ii) advection of the large-scale field from an external source (e.g. the companion star in X-ray binaries). In the talk, I shall discuss efficiency of both the processes, which we investigated using high-resolution 3D global MHD and GRMHD simulations respectively. In the first part of the talk, I shall talk about our work on magnetorotational instability (MRI) driven dynamo in a geometrically thick RIAF, studied using MHD simulations. We used the mean-field paradigm to describe the dynamo action. After giving a brief overview of mean field dynamo, I shall talk about the characterization methods of dynamo coefficients and their astrophysical implications. In the second part of the talk, I shall touch upon our recent results of magnetic flux transport in a RIAF using GRMHD simulations.