Deflection angle of light for an observer and source at finite distance from a rotating global monopole (1811.01739v2)

Abstract: By using a method improved with a generalized optical metric, the deflection of light for an observer and source at finite distance from a lens object in a stationary, axisymmetric and asymptotically flat spacetime has been recently discussed [Ono, Ishihara, Asada, Phys. Rev. D {\bf 96}, 104037 (2017)]. In this paper, we study a possible extension of this method to an asymptotically nonflat spacetime. We discuss a rotating global monopole. Our result of the deflection angle of light is compared with a recent work on the same spacetime but limited within the asymptotic source and observer [Jusufi et al., Phys. Rev. D {\bf 95}, 104012 (2017)], in which they employ another approach proposed by Werner with using the Nazim's osculating Riemannian construction method via the Randers-Finsler metric. We show that the two different methods give the same result in the asymptotically far limit. We obtain also the corrections to the deflection angle due to the finite distance from the rotating global monopole. Near-future observations of Sgr A${}^{*}$ will be able to put a bound on the global monopole parameter $\beta$ as $1- \beta < 10^{-3}$ for a rotating global monopole model, which is interpreted as the bound on the deficit angle $\delta < 8\times 10^{-4}$ [rad].