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Abstract The Event Horizon Telescope (EHT) has produced images of the plasma flow around the supermassive black holes in Sgr A* and M87* with a resolution comparable to the projected size of their event horizons. Observations with the next-generation Event Horizon Telescope (ngEHT) will have significantly improved Fourier plane coverage and will be conducted at multiple frequency bands (86, 230, and 345 GHz), each with a wide bandwidth. At these frequencies, both Sgr A* and M87* transition from optically thin to optically thick. Resolved spectral index maps in the near-horizon and jet-launching regions of these supermassive black hole sources can constrain properties of the emitting plasma that are degenerate in single-frequency images. In addition, combining information from data obtained at multiple frequencies is a powerful tool for interferometric image reconstruction, since gaps in spatial scales in single-frequency observations can be filled in with information from other frequencies. Here we present a new method of simultaneously reconstructing interferometric images at multiple frequencies along with their spectral index maps. The method is based on existing regularized maximum likelihood (RML) methods commonly used for EHT imaging and is implemented in theeht-imagingPython software library. We show results of this method on simulated ngEHT data sets as well as on real data from the Very Long Baseline Array and Atacama Large Millimeter/submillimeter Array. These examples demonstrate that simultaneous RML multifrequency image reconstruction produces higher-quality and more scientifically useful results than is possible from combining independent image reconstructions at each frequency.
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This content will become publicly available on July 1, 2027
Multifrequency Synthesis via CHIBI: Colorful Hierarchical Interferometric Bayesian Imaging
Abstract From magnetized plasma of relativistic jets to dust grains within protoplanetary disks, we study the emission mechanisms of radio sources via their rich spectral structure. Multifrequency synthesis (MFS) is a technique in which interferometric data at multiple frequencies are imaged simultaneously, resulting in a denser sampling of spatial scales, higher imaging fidelity, and tighter constraints on the source’s spectral structure and evolution. We describe a new method of MFS imaging reconstruction in a hierarchical interferometric Bayesian inference framework, CHIBI. The model parameterization is based on the spectral behavior of synchrotron radiation, the emission mechanism dominating the radio emission observed from galactic nuclei. We show results of this method on observations of jet sources from the MOJAVE catalog with the Very Long Baseline Array, and showcase the prospects for MFS imaging of M87* with simulated data from the Event Horizon Telescope (EHT) and future expansions such as the next-generation EHT and the black hole Explorer. These demonstrations highlight the benefit of MFS to reconstruct higher-fidelity images and spectral index maps, producing scientifically richer results in a statistically grounded framework, implemented inComrade.jl.
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- PAR ID:
- 10701100
- Publisher / Repository:
- IOP
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 1005
- Issue:
- 2
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 132
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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