$\texttt{Jipole}$: A Differentiable $\texttt{ipole}$-based Code for Radiative Transfer in Curved Spacetimes
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| Format: | Preprint |
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2025
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| author | Motta, Pedro Naethe Prather, Ben S. Cárdenas-Avendaño, Alejandro |
| author_facet | Motta, Pedro Naethe Prather, Ben S. Cárdenas-Avendaño, Alejandro |
| contents | Recent imaging of supermassive black holes by the Event Horizon Telescope (EHT) has relied on exhaustive parameter-space searches, matching observations to large, precomputed libraries of theoretical models. As observational data become increasingly precise, the limitations of this computationally expensive approach grow more acute, creating a pressing need for more efficient methods. In this work, we present $\texttt{Jipole}$, an automatically differentiable (AD), $\texttt{ipole}$-based code for radiative transfer in curved spacetimes, designed to compute image gradients with respect to underlying model parameters. These gradients quantify how parameter changes-such as the black hole's spin or the observer's inclination-affect the image, enabling more efficient parameter estimation and reducing the number of required images. We validate $\texttt{Jipole}$ against $\texttt{ipole}$ in two analytical tests and then compare pixel-wise intensity derivatives from AD with those from finite-difference methods. We then demonstrate the utility of these gradients by performing parameter recovery for an analytical model using a conjugate gradient optimizer in three increasingly complex cases for the injected image: ideal, blurred, and blurred with added noise. In most cases, high-accuracy fits are obtained in only a few optimization steps, failing only in cases with extremely low signal-to-noise ratios and large blurring size kernels. These results highlight the potential of AD-based methods to accelerate robust, high-fidelity model-data comparisons in current and future black hole imaging efforts. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2509_07065 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | $\texttt{Jipole}$: A Differentiable $\texttt{ipole}$-based Code for Radiative Transfer in Curved Spacetimes Motta, Pedro Naethe Prather, Ben S. Cárdenas-Avendaño, Alejandro High Energy Astrophysical Phenomena Instrumentation and Methods for Astrophysics General Relativity and Quantum Cosmology Recent imaging of supermassive black holes by the Event Horizon Telescope (EHT) has relied on exhaustive parameter-space searches, matching observations to large, precomputed libraries of theoretical models. As observational data become increasingly precise, the limitations of this computationally expensive approach grow more acute, creating a pressing need for more efficient methods. In this work, we present $\texttt{Jipole}$, an automatically differentiable (AD), $\texttt{ipole}$-based code for radiative transfer in curved spacetimes, designed to compute image gradients with respect to underlying model parameters. These gradients quantify how parameter changes-such as the black hole's spin or the observer's inclination-affect the image, enabling more efficient parameter estimation and reducing the number of required images. We validate $\texttt{Jipole}$ against $\texttt{ipole}$ in two analytical tests and then compare pixel-wise intensity derivatives from AD with those from finite-difference methods. We then demonstrate the utility of these gradients by performing parameter recovery for an analytical model using a conjugate gradient optimizer in three increasingly complex cases for the injected image: ideal, blurred, and blurred with added noise. In most cases, high-accuracy fits are obtained in only a few optimization steps, failing only in cases with extremely low signal-to-noise ratios and large blurring size kernels. These results highlight the potential of AD-based methods to accelerate robust, high-fidelity model-data comparisons in current and future black hole imaging efforts. |
| title | $\texttt{Jipole}$: A Differentiable $\texttt{ipole}$-based Code for Radiative Transfer in Curved Spacetimes |
| topic | High Energy Astrophysical Phenomena Instrumentation and Methods for Astrophysics General Relativity and Quantum Cosmology |
| url | https://arxiv.org/abs/2509.07065 |