Using multi-wavelength correlations to understand blazar physics

Abstract

Blazars are a subclass of Active Galactic Nuclei (AGN) with a jet pointing toward the observer’s line of sight. These objects are highly variable, violent emitters of non-thermal radiation from radio to gamma-rays. The Hartebeesthoek Radio Astronomy Observatory (HartRAO) has been monitoring AGNs since the 1970s and has established itself as a key contributor of radio observations in the southern hemisphere, particularly for sources south of 30 that are beyond the reach of most northern telescopes. Currently, the HartRAO 26-m radio telescope monitors over 40 continuum and spectral line sources without a dedicated data reduction and analysis software package. This has resulted in a backlog of unprocessed observations, including critical observations necessary for the observatory’s operations. In this work, I present a software solution for the HartRAO data reduction and analysis problem and test it on three blazar sources monitored at HartRAO in a multi-wavelength study. My project is arranged in two parts.

The first part of my project is a scientific investigation into the potential correlated relationships in multi-wavelength light curves of three HartRAO-monitored blazar sources to establish whether multi-resolution data can be used to support the models claiming that the higher energy gamma-ray emission leads the radio. Using the discrete correlation function (DCF), I estimate the correlations and time lags between the radio and gamma-ray wavelengths of my sample and find positive correlations with the gamma-rays leading the radio wavelengths by ≥ 100 to 200 days, which supports existing literature on the topic. These time lags represent the delay between the emission of gamma-rays and radio wavelengths and provide insight into the physical processes occurring in the blazar’s jet, particularly the processes that lead to the emission of non-thermal radiation, an aspect of AGN studies that is still poorly understood

The second part of my project focuses on the technical challenges of data reduction and analysis at HartRAO. I describe how data calibration is performed at HartRAO and test and evaluate the calibration processes to ensure the validity of the results. I also develop a software solution for the continuum data reduction and analysis of HartRAO data. The proposed solution includes a data reduction pipeline that utilizes an SQLite database to store the reduced and intermediate data products, as well as a user-friendly graphical user interface (GUI) for easy and quick processing of data. The new software provides the option to perform both batch and single-file processing and provides better performance compared to the old spectroscopy analysis program (LINES), previously used to process continuum data. By providing a software solution for data reduction and analysis, this thesis will enable HartRAO to make use of the critical observations that are currently backlogged and improve the observatory’s operations