Strong gravitational lensing by a Reissner-Nordström naked singularity with a marginally unstable photon sphere
arXiv:2504.00355 · doi:10.1103/7r5r-nlcj
Abstract
We investigate strong gravitational lensing by a marginally unstable photon sphere in a Reissner-Nordström naked singularity spacetime. Using the Picard-Fuchs equation, we derive full-order power series expressions for the deflection angle in various regimes, including the strong deflection limits from both outside and inside the photon sphere. We show that the deflection angle diverges non-logarithmically in both cases, refining existing asymptotic formulae. Comparing truncated approximations with numerical results, we find that higher-order corrections are essential to achieve comparable accuracy to logarithmic divergence cases. Using these improved formulae, we also derive precise approximations for image positions that are not restricted to the almost perfectly aligned cases.
20 pages, 5 figures, minor corrections, references added
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Cited by in corpus (3)
- Strong-deflection expansion of the deflection angle near a degenerate photon sphere
- Gravitational lensing inside and outside of a marginally unstable photon sphere in a general, static, spherically symmetric, and asymptotically-flat spacetime in strong deflection limits
- Strong deflection of massive particles via the geodesic deviation equation