Finite-source magnification residuals from a cNFW-inspired perturbation of an effective spinning black hole binary lens
Abstract
We ask whether a cored-NFW-inspired radial perturbation leaves a finite-source magnification residual after refitting the best effective spinning vacuum binary. We compute the source flux by direct image-plane integration and vary the lens scale, separation, mass ratio, two spin magnitudes, two projected spin directions, and one phase shift. After refitting, the caustics and magnification curves are almost identical and the phase shift is nearly zero. Still, a structured residual remains. At the highest resolution, the full-orbit rms residual is 1.61×10−2 and the maximum local residual is 4.41×10−2. Increasing the grid from 800×522 to 1000×653 changes the full-orbit rms by only 3.39×10−5. The residual also survives nine tests with Gaussian, uniform, and tapered sources at three RMS-size factors. Thus, a finite-source residual survives strong geometric degeneracy in this effective model. We do not claim a unique dark-matter detection or a prediction for a physically scaled binary.
Versions
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BibTeX
@misc{fathi2026finitesource,
title = {{Finite-source magnification residuals from a cNFW-inspired perturbation of an effective spinning black hole binary lens}},
author = {Mohsen Fathi},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2607.23300},
eprint = {2607.23300},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.23300},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Finite-source magnification residuals from a cNFW-inspired perturbation of an effective spinning black hole binary lens
AU - Mohsen Fathi
PY - 2026
DA - 2026/09/27
PB - arXiv
DO - 10.48550/arxiv.2607.23300
UR - https://arxiv.org/abs/2607.23300
AB - We ask whether a cored-NFW-inspired radial perturbation leaves a finite-source magnification residual after refitting the best effective spinning vacuum binary. We compute the source flux by direct image-plane integration and vary the lens scale, separation, mass ratio, two spin magnitudes, two projected spin directions, and one phase shift. After refitting, the caustics and magnification curves are almost identical and the phase shift is nearly zero. Still, a structured residual remains. At the highest resolution, the full-orbit rms residual is 1.61×10^−2 and the maximum local residual is 4.41×10^−2. Increasing the grid from 800×522 to 1000×653 changes the full-orbit rms by only 3.39×10^−5. The residual also survives nine tests with Gaussian, uniform, and tapered sources at three RMS-size factors. Thus, a finite-source residual survives strong geometric degeneracy in this effective model. We do not claim a unique dark-matter detection or a prediction for a physically scaled binary.
ER -