24-27 October 2023
Europe/Berlin timezone

Scientific Programme

contributed talks (on Thursday at 1 pm, Library 2.05)


1.MOEA/D: Multi-Objective Optimization for Polarimetric Dynamic Reconstructions from Interferometric Data (Alejandro Mus)

Forward modeling RML methods are a powerful tool for reconstructing interferometric data. However, the hyper-parameters weighting data terms and regularizers must be known a priori. To determine these parameters, extensive and costly surveys are conducted, involving the exploration of a vast number of different hyper-parameter combinations. For example, in the case of SgrA*, the Event Horizon Telescope Collaboration (EHTC) explored approximately 7 million combinations.

In this presentation, I will introduce our method, MOEA/D, which is a multi-objective optimization formulation designed for static and dynamic Stokes I and polarimetry reconstructions. MOEA/D addresses two critical limitations of current RML methods: it eliminates the need for a hyper-parameter survey and handles the multimodality of the non-convex functional.

First, I will explain how MOEA/D can be applied to static imaging reconstruction, providing essential concepts to grasp the problem and the solution. Then, I will discuss a recently submitted paper in which we extend MOEA/D to include dynamics and polarimetry, enabling us to recover movies and polarized images from interferometric data.

By combining these two extensions, MOEA/D II, along with DoG-HiT, stands out as one of the two RML methods capable of recovering polarimetric movies.

To conclude, in this presentation, I will also discuss the current extensions of MOEA/D, including the inclusion of Stokes V and scattering screen reconstruction. Our goal is to achieve a comprehensive dynamic reconstruction of SgrA* in full Stokes polarization, along with its associated scattering screen.


2.Radiative processes in black hole magnetospheres (Arman Tursunov)

Magnetic fields surrounding black holes are responsible for a variety of astrophysical phenomena related to accretion processes and relativistic jets. Depending on the source, the strength and configuration of the field lines may differ significantly, which can, in turn, affect the trajectories of charged particles and the corresponding observables. In this talk, I will review some most known solutions to electromagnetic fields around black holes and discuss the observational signatures of processes occurring within the black hole magnetospheres.


3.Bayesian Imaging with Resolve

Component separation & multi-frequency modelling (Richard Fuchs)

Recent large radio interferometric arrays provide big datasets with wide-field multi-frequency observations that can contain plenty of different objects like radio galaxies and point sources. Possible improvements in image quality together with uncertainty estimation motivate their re-investigation by the Bayesian imaging algorithm resolve. For this purpose, the basic single-frequency model of resolve needs to be extended to a multi-object that is capable of separating components and handling multi-frequency data.
Together, these new features allow multi-frequency analysis of diffuse emission and point sources in an observed environment. Moreover, it is possible to resolve important parts of the emission field like radio galaxies with higher resolution by placing tuneable boxes at these locations that harbour the different object models. These enhancements can improve the image quality and yield sensible results for the sky brightness distribution and spectral index maps.