Using multi-wavelength correlations to understand blazar physics
Date
2024
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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
Description
A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Faculty of Science, School of Physics, University of the Witwatersrand, Johannesburg, 2023
Keywords
Blazars, Data reduction, Active galactic nuclei