Investigating the Nature of High Energy Emission in Active Galactic Nuclei
Abstract
Active Galactic Nuclei (AGN) are extremely luminous objects that reside at the center of some galaxies. Radio loud AGN possess jets of plasma emanating from the center of their host galaxy. These jets are very bright at radio frequencies. Blazars are the most extreme subset of radio loud AGN, they are violently variable across the electromagnetic spectrum, highly polarized and their radio jets often show superluminal motion. The most likely explanation for the unusual properties of blazars is that their jets are pointed close to our line of sight. We study the high-energy emission mechanisms of blazars because gamma-rays account for a large fraction of the total energy emitted by blazars. Therefore, understanding the mechanisms of gamma-ray production in blazars is crucial to an overall understanding of how these objects work. In this dissertation we attempt to identify the basic mechanisms of gamma-ray emission in individual blazars by simultaneously monitoring their flux densities across the electromagnetic spectrum (radio though gamma-rays). We staged multi-wavelength observing campaigns using ground based and space based observatories for four blazars during active and quiescent gamma-ray states. Data from these campaigns are compiled into broadband spectral energy distributions (SEDs) ranging from radio to gamma-ray energies. The broadband SEDs are then fit with a one zone leptonic model of blazar emission in order to establish the most likely gamma-ray emission mechanism. One non-blazar radio loud AGN, 3C84, at the core of the galaxy NGC 1275 is studied in depth using the VLBA. Blazars and other radio loud AGN only differ by the viewing angle thus the same physical processes are common in both types of objects. The AGN 3C84 is interesting because it is nearby (z=0.017559), it is the brightest member of the Perseus cluster, and it is one of the few non-aligned gamma-ray emitting AGN. We obtained six epochs of data, at 22 and 43 gHz, with the VLBA and we constructed a map of the spectral index for every epoch. We find a pattern in the flares that we have modeled. Some flares can be fit by adjusting only the electron energy distribution while others require changes in other parameters in the model, such as the magnetic field or the size of the emitting region. We find two flat spectrum components in the parsec scale structure of 3C84. We do not see any obvious correlation between the parsec scale radio activity in the jet of 3C84 and its gamma-ray emission levels.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 2014
- Bibcode:
- 2014PhDT........40D
- Keywords:
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- Physics, Astronomy and Astrophysics;Physics, Elementary Particles and High Energy