Observation of Active Galactic Nuclei in the gamma-ray band using the first telescope of the CTA North

Abstract

Since humanity first gazed upon the night sky, our curiosity has perpetually sought to unveil the mysteries concealed beyond the celestial canopy of dark, starry expanse. We developed and refined our theoretical and observational tools to understand these mysteries. Observational astronomy, crucial to our exploration, can be categorized based on the type of signals or messengers used for observing the Universe. In modern times, this classification extends beyond traditional electromagnetic radiation to encompass phenomena like gravitational waves, cosmic rays, and elusive particles such as neutrinos. _x000D_ _x000D_ Gamma rays are one of the messengers employed to observe the non-thermal Universe. The astrophysical phenomena that lead to the production of energetic gamma rays are also likely to produce Cosmic rays. However, in contrast to Cosmic rays, gamma rays are not subject to deviations in their trajectories caused by magnetic fields. CTA is one of the next-generation instruments being deployed for gamma-ray astronomy, and it will be the first open ground-based gamma-ray observatory and the largest Imaging Atmospheric Cherenkov Telescope (IACT) array. With this new observatory, we will be able to significantly enhance the detection capabilities compared to the current ground-based gamma-ray instruments, ushering in a new era of multi-messenger astronomy. _x000D_ _x000D_ One of the important astrophysical sources responsible for the production of high-energy gamma rays is the Active Galactic Nucleus (AGN), which are the central regions of some galaxies. They are usually assumed to host a Super Massive Black Hole (SMBH) at their core, which plays the crucial role of the engine of such extreme physics. These objects are studied extensively in the full Electromagnetic (EM) spectrum, providing key insights into their morphology and energetic characteristics. They also can help study the evolution of the Universe, for example by supporting the indirect measurement of the Extragalactic Background Light (EBL). The EBL is the net thermal emission from stars and galaxies, forming the ambient photon background in the optical and infrared wavelengths. We can_x000D_ understand the amount of the EBL by measuring the amount of VHE flux of sources like the AGN, being absorbed by the photon-photon interaction with the EBL._x000D_ _x000D_ In this thesis, I explore the first Large-Sized Telescope (LST-1) of the CTA and discuss the implementation of its data analysis pipeline by analysing the first AGNs detected by it. I have helped develop the LST-1-specific data analysis software cta-lstchain to create "science-ready" DL3 data, such that it can be analyzed using the CTA Science Tool gammapy. Analyzing the AGNs with LST-1 has been my main focus in this thesis. To support joint analysis of LST-1 data with the public Fermi-LAT data, I also developed a gammapy-wrapper pipeline, asgardpy. Using select datasets of AGN observations, I tried to constrain the EBL density as per 5 EBL_x000D_ models.

Date of Award	26 Apr 2024
Original language	English
Supervisor	Abelardo Moralejo Olaizola (Director)