| Abstract : | Black holes (BHs) are one of the most exotic objects found in the Universe. They fall into a class of objects called compact-objects. Apart from BHs, neutron stars (NSs) and white dwarfs also fall into this classification. Due to their large compactness, they exhibit a phenomenon called accretion, which carries imprints of the nature of the central object. Thus modelling of accretion flows is necessary. One of the processes that play a significant role in the accretion physics of a BH system is the production of electron-positron pairs and their annihilation. We found in this thesis that a distinct annihilation bump is present in the spectrum, along with an increase in luminosity. The above work was done in one-temperature regime. These solutions are important since they can extract the essential qualitative features of the flow without getting involved into the other complexities of an accreting system. But, to accurately measure the luminosity and spectra, one needs to have information of electron temperature (Te) inside the flow, which may or may not be comparable to the proton temperature (Tp). One of the major problems present in two-temperature theory is ‘degeneracy’. This is caused because of the increase in the number of flow variables (Te and Tp instead of a single T), without any increase in the number of governing equations. A novel methodology was proposed in this thesis to remove the degeneracy, such that a given set of constants of motion harbour a unique solution. We validated the proposed methodology on different compact objects and types of accretion flows (spherical, rotating and accretion along magnetic funnels). After constraining degeneracy, we analysed the spectrum of the unique solutions. Thus, in short, this thesis aims to study accretion flows around compact objects, alongwith analysing their spectrum, for a broad range of parameter-space. |
