VIMAP: an Interactive Program Providing Radio Spectral Index Maps of Active Galactic Nuclei

TL;DR

VIMAP is an interactive Python tool that creates radio spectral index maps of AGN from VLBI data, addressing alignment challenges and aiding spectral analysis of AGN jets.

Contribution

The paper introduces VIMAP, a novel GUI-based Python program that facilitates spectral index mapping of AGN using VLBI data with improved alignment techniques.

Findings

Successfully applied VIMAP to archival VLBI maps of 3C 120.

Demonstrated VIMAP's effectiveness in spectral analysis of AGN jets.

Addresses VLBI map alignment challenges with a cross-correlation algorithm.

Abstract

We present a GUI-based interactive Python program, VIMAP, which generates radio spectral index maps of active galactic nuclei (AGN) from Very Long Baseline Interferometry (VLBI) maps obtained at different frequencies. VIMAP is a handy tool for the spectral analysis of synchrotron emission from AGN jets, specifically of spectral index distributions, turn-over frequencies, and core-shifts. In general, the required accurate image alignment is difficult to achieve because of a loss of absolute spatial coordinate information during VLBI data reduction (self-calibration) and/or intrinsic variations of source structure as function of frequency. These issues are overcome by VIMAP which in turn is based on the two-dimensional cross-correlation algorithm of Croke and Gabuzda (2008). In this paper, we briefly review the problem of aligning VLBI AGN maps, describe the workflow of VIMAP, and present an analysis of archival VLBI maps of the active nucleus 3C 120.