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Propagation delays and regional intensity changes in lensed hotspot images

  • Yong Li
  • Xiao-Gang Lan
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Abstract

Propagation delays cause an image recorded at a single observer time to combine radiation emitted at different stages of the source evolution. Comparable changes in total intensity can accompany distinct and even opposite changes in apparent image size. Using regional intensities, centroids, and covariances, we apply the law of total covariance to separate changes in regional intensity weights from changes in internal widths and centroid separation. Ray tracing simulations of a finite Gaussian hotspot moving along a prescribed strong field trajectory show two events with comparable attenuation in screen integrated intensity but opposite changes in second moment size. In the contracting event, the regional weights move away from balance; in the expanding event, they move toward balance even as the centroids approach each other. Differential propagation delays therefore drive these opposite size responses by redistributing intensity between spatially separated image regions.

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Cite

BibTeXRIS
BibTeX
@misc{li2026propagation,
  title = {{Propagation delays and regional intensity changes in lensed hotspot images}},
  author = {Yong Li and Xiao-Gang Lan},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.30701},
  eprint = {2609.30701},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.30701},
}
RIS
TY  - UNPB
TI  - Propagation delays and regional intensity changes in lensed hotspot images
AU  - Yong Li
AU  - Xiao-Gang Lan
PY  - 2026
DA  - 2026/09/25
PB  - arXiv
DO  - 10.48550/arxiv.2609.30701
UR  - https://arxiv.org/abs/2609.30701
AB  - Propagation delays cause an image recorded at a single observer time to combine radiation emitted at different stages of the source evolution. Comparable changes in total intensity can accompany distinct and even opposite changes in apparent image size. Using regional intensities, centroids, and covariances, we apply the law of total covariance to separate changes in regional intensity weights from changes in internal widths and centroid separation. Ray tracing simulations of a finite Gaussian hotspot moving along a prescribed strong field trajectory show two events with comparable attenuation in screen integrated intensity but opposite changes in second moment size. In the contracting event, the regional weights move away from balance; in the expanding event, they move toward balance even as the centroids approach each other. Differential propagation delays therefore drive these opposite size responses by redistributing intensity between spatially separated image regions.
ER  -