Name: Shilpa Sarkar
Affiliation: Aryabhatta Research Institute of Observational Sciences (ARIES)
Conference ID : ASI2022_46
Title : Funnel flows around strongly magnetised neutron stars
Authors : Shilpa Sarkar, Indranil Chattopadhyay, Kuldeep Singh
Abstract Type: Oral
Abstract Category : Extragalactic Astronomy
Abstract : Neutron stars are one of the exotic and densest objects found in the Universe, with core densities surpassing nuclear densities. They harbour very strong magnetic fields (10^8−15 G) near the surface which dictates the dynamics of the accreted matter. The accretion generally takes place in the form of an accretion disc upto a certain radius after which matter is strictly channeled in the form of accretion funnels along the field lines, until it reaches the poles of the star. The radiation obtained from these systems allows us to investigate the underlying physics present and help probe deeper the nature of these objects. Since electrons are the ones which radiate, an exact computation of the spectrum requires working in the two-temperature regime, which is not trivial. This regime is degenerate because the number of unknowns is more than the set of equations. We hence proposed a general methodology to obtain unique two-temperature transonic accretion solutions around NSs in the ideal magneto-hydrodynamic (MHD) regime. After identifying the correct solution, we analysed the solutions and the corresponding spectrum for a global range of parameter space. The hard surface of an NS always ensures the formation of a primary shock just near the surface. This shock is responsible for the slowing down of the accreted matter and 99.99% of the total luminosity as seen by a distant observer. In addition a secondary shock might also form for a given range of flow parameters. There is a distinct extended emission spectral signature at higher energies of this shock. We also discuss the effect of NS spin and magnetic field on the spectra of the Nss.