PhD Defense: Aamil Shaik
Location
Physics : 401
PhD Defense: Aamil Shaik – Online Event
Date & Time
August 25, 2023, 12:00 pm – 2:00 pm
Description
ADVISOR: Dr. Eileen Meyer
TITLE: Variability and spectral properties of large-scale extragalactic X-ray jets
ABSTRACT:At the center of most massive galaxies lies a supermassive black hole (10^6-10^10 solar masses). A small percentage of these accrete matter at a high rate and are consequently called active galactic nuclei (AGN). In some AGN, this accretion powers large jets of relativistic plasma which can extend up to lengths of Megaparsecs. While these kpc-scale jets were initially detected at radio frequencies where they emit brightly via synchrotron radiation, they have since been found to produce high luminosities across the electromagnetic spectrum. Of particular interest to this thesis is the Chandra X-ray Observatory's discovery of bright X-ray emission from most high-power kpc-scale jets which appears as a separate spectral component from the primary synchrotron component that extends from radio to infrared to optical. Despite two decades of research, the origin of this X-ray emission remains unknown, with competing models such as relativistic beaming of inverse-Compton upscattering of Cosmic Microwave Background (IC-CMB) photons and synchrotron radiation from a high-energy electron population predicting vastly different conditions within the jet.
In this dissertation, I present two studies investigating the mechanism behind the bright X-ray emission from kpc-scale jets. The first study is a population survey of X-ray emitting jets for X-ray variability over time which is impossible to reconcile with a beamed IC-CMB model. I used a novel statistical method based on a maximum likelihood model to analyze archival Chandra data for a sample of 53 jets. Ultimately, I find significant evidence to suggest that a significant fraction of kpc-scale jets are variable X-ray emitters and thus reject IC-CMB as the dominant source of X-rays within those jets.
The second project is a case study of the western hot spot of the nearby jetted AGN Pictor A using recent deep \emph{NuSTAR} exposures in combination with archival Chandra data. This study represents the first study of a kpc-scale jet at hard X-ray energies (>10 keV). Using a Bayesian approach, I achieved the strongest constraints on the wide X-ray spectrum to date. I also applied our variability analysis from the previous study using both our NuSTAR and Chandra data, and found the most significant detection of variability in a kpc-scale X-ray jet yet. Collectively, these results suggest a synchrotron origin for the kpc-scale X-ray emission from extremely compact and highly magnetized unresolved emitting regions within the jet. This represents a fundamental change in how we view jet structure and particle acceleration.
TITLE: Variability and spectral properties of large-scale extragalactic X-ray jets
ABSTRACT:At the center of most massive galaxies lies a supermassive black hole (10^6-10^10 solar masses). A small percentage of these accrete matter at a high rate and are consequently called active galactic nuclei (AGN). In some AGN, this accretion powers large jets of relativistic plasma which can extend up to lengths of Megaparsecs. While these kpc-scale jets were initially detected at radio frequencies where they emit brightly via synchrotron radiation, they have since been found to produce high luminosities across the electromagnetic spectrum. Of particular interest to this thesis is the Chandra X-ray Observatory's discovery of bright X-ray emission from most high-power kpc-scale jets which appears as a separate spectral component from the primary synchrotron component that extends from radio to infrared to optical. Despite two decades of research, the origin of this X-ray emission remains unknown, with competing models such as relativistic beaming of inverse-Compton upscattering of Cosmic Microwave Background (IC-CMB) photons and synchrotron radiation from a high-energy electron population predicting vastly different conditions within the jet.
In this dissertation, I present two studies investigating the mechanism behind the bright X-ray emission from kpc-scale jets. The first study is a population survey of X-ray emitting jets for X-ray variability over time which is impossible to reconcile with a beamed IC-CMB model. I used a novel statistical method based on a maximum likelihood model to analyze archival Chandra data for a sample of 53 jets. Ultimately, I find significant evidence to suggest that a significant fraction of kpc-scale jets are variable X-ray emitters and thus reject IC-CMB as the dominant source of X-rays within those jets.
The second project is a case study of the western hot spot of the nearby jetted AGN Pictor A using recent deep \emph{NuSTAR} exposures in combination with archival Chandra data. This study represents the first study of a kpc-scale jet at hard X-ray energies (>10 keV). Using a Bayesian approach, I achieved the strongest constraints on the wide X-ray spectrum to date. I also applied our variability analysis from the previous study using both our NuSTAR and Chandra data, and found the most significant detection of variability in a kpc-scale X-ray jet yet. Collectively, these results suggest a synchrotron origin for the kpc-scale X-ray emission from extremely compact and highly magnetized unresolved emitting regions within the jet. This represents a fundamental change in how we view jet structure and particle acceleration.
