DR. PRASUN DHANG

Jets are generally observed in the low/hard state of a transient black hole binary (BHB). Jet production is thought to be connected to the presence of a radiatively inefficient accretion flow (RIAF) and a large-scale magnetic field close to the accreting black hole (BH). However, the source of the large scale field is not quite obvious. It is possible to have an in-situ generation of the magnetic field in the accretion flow by the dynamo action. By performing 3D global MHD simulations, we investigate the magnetorotational instability (MRI) driven dynamo in a geometrically thick (H/R ~1) RIAF. We use the mean-field paradigm to describe the dynamo action in the RIAF. We observe an intermittent dynamo cycle unlike the regular cycles seen in the simulations of a geometrically thin (H/R<<1) standard disc. Intermittency in the dynamo cycle is related to the slightly sub-Keplerian nature of the angular velocity. For the first time, we also obtain the spatial distribution of the turbulent dynamo coefficients in the poloidal plane (r, \theta) for the MRI dynamo in the accretion flow. We find the evidence of a weak \alpha-effect and the presence of a strong turbulent pumping transporting mean magnetic fields radially outward. We conclude that dynamo action is inefficient in generating ordered large-scale magnetic field in the RIAF. Assuming a truncated disc to exist in the low/hard state of BHBs, we propose a plausible scenario where the ordered large-scale magnetic fields can be accumulated close the BH giving rise to a favourable condition for the production of the jets.