Deflection angle in the strong deflection limit in a general asymptotically flat, static, spherically symmetric spacetime

摘要

Gravitational lensing by the light sphere of compact objects like black holesand wormholes will give us information on the compact objects. In this paper,we provide an improved strong deflection limit analysis in a generalasymptotically flat, static, spherically symmetric spacetime. The strongdeflection limit analysis also works in ultrastatic spacetimes. As an exampleof an ultrastatic spacetime, we reexamine the deflection angle in the strongdeflection limit in an Ellis wormhole spacetime. Using the strong deflectionlimit, we obtain the deflection angle analytically for the Reissner-Nordstromspacetime. The point of the improvement is the definition of a standardvariable in the strong deflection limit analysis. We show that the choice ofthe variable is as important as the choice of the coordinates and we concludethat one should choose a proper variable for a given spacetime.