Optical Polarimetry and Gamma-Ray Observations of a Sample of Radio-Loud Narrow Line Seyfert 1 Galaxies
Date of Award
Doctor of Philosophy (PhD)
Physics and Astronomy
H. Richard Miller
The recent discovery of a new population of Active Galactic Nuclei (AGN) – the Radio Loud Narrow Line Seyfert 1 (RL NLS1) galaxies – at g-ray energies by Fermi has prompted intense interest among researchers, as evidence mounts that these objects may in fact compose a new class of blazars. If RL NLS1s are indeed a new class of blazars, or at least analogous to them, then the detection of certain blazar-like properties would be expected. These properties include significant variability at all wavelengths across the electromagnetic spectrum and on timescales from minutes to years, significant & variable polarization in the radio and optical regimes, significant & variable high-energy emissions (especially in the g-ray regime), and a double-peaked structure of their spectral energy distributions.
This dissertation seeks to characterize several of these properties for RL NLS1s as a class. These include the degree to which these objects are polarized and the variability of this property, the detection and characterization of these sources at g-ray energies with the Large Area Telescope aboard the Fermi spacecraft, and the degree to which these properties are interdependent. A photopolarimetric survey (the first of its kind for this class of objects) and g-ray monitoring program were conducted by the author in order to obtain the data necessary for this project. The measurements obtained via these observations are used to characterize this interesting class of objects with respect to a sample of blazars. In general, it was found that the polarizations of these objects fall between radio-quiet NLS1s and FSRQ-type blazars, and were most similar to HBL-type blazars. The 7 RL NLS1s in this sample that had been detected above a Test Statistic (TS) of 25 by Fermi/LAT were most similar to FSRQs, while 9 objects detected in the interval 9 < TS < 25 shared several properties with HBLs. Two RL NLS1s - J1443+4725 and J1644+2619 - are identified as high-confidence (TS > 25) g-ray sources for the first time, bringing the total number of members of this class firmly detected at g-ray energies to 8. The gamma-ray spectra of RL NLS1s are similar to FSRQs, though some have steeper spectra.
Eggen, Joseph, "Optical Polarimetry and Gamma-Ray Observations of a Sample of Radio-Loud Narrow Line Seyfert 1 Galaxies." Dissertation, Georgia State University, 2014.