Multi-frequency synthesis algorithm based on Generalized Maximum Entropy Method. Application to 0954+658

TL;DR

This paper introduces a multi-frequency synthesis algorithm based on a generalized maximum entropy method that accounts for spectral variations and core shifts, improving imaging and spectral index mapping of radio sources.

Contribution

The paper presents a novel multi-frequency synthesis algorithm using a generalized maximum entropy approach capable of reconstructing sign-variable functions and correcting for core shifts.

Findings

Algorithm successfully applied to simulated data

Improved total intensity and spectral index images of 0954+658

Effective correction for frequency-dependent core position shifts

Abstract

We propose the multi-frequency synthesis (MFS) algorithm with spectral correction of frequency-dependent source brightness distribution based on maximum entropy method. In order to take into account the spectral terms of n-th order in the Taylor expansion for the frequency-dependent brightness distribution, we use a generalized form of the maximum entropy method suitable for reconstruction of not only positive-definite functions, but also sign-variable ones. The proposed algorithm is aimed at producing both improved total intensity image and two-dimensional spectral index distribution over the source. We consider also the problem of frequency-dependent variation of the radio core positions of self-absorbed active galactic nuclei, which should be taken into account in a correct multi-frequency synthesis. First, the proposed MFS algorithm has been tested on simulated data and then applied to four-frequency synthesis imaging of the radio source 0954+658 from VLBA observational data obtained quasi-simultaneously at 5, 8, 15 and 22 GHz.