Parsec scale intra-day variability in radio selected blazars: A MOJAVE study
Abstract
In this dissertation, the results of a study of the Intra–day Variability (IDV) properties of a sample of blazars, which are regularly monitored under the MOJAVE (Monitoring Of Jets in AGN with VLBA Experiments) program [Lister & Homan, 2005], are presented. A novel 'Gain Transfer' methodology, developed by the MOJAVE team, was used to study the parsec (pc) scale IDV properties of blazars using VLBA data, for the first time. Where data were available, brightness temperature and Doppler factors were also estimated. The present study covers VLBA epochs from 1994 to 2011. Approximately 3800 light curves, from about 390 AGN comprising the full sample, were analyzed for IDV. IDV was detected in ∼ 28% of sources, and ∼ 11% of epochs. When only the 131 AGN from the statistically complete, flux density limited MOJAVE_1 sample were considered, IDV was detected in ∼ 61.8% of sources and ∼ 15.2% epochs. Beaming indicators, such as equipartition Doppler factor (δeq) & apparent speed (βapp ), were found to be positively correlated with IDV, while the galactic latitude position of the source was found to be negatively correlated with IDV. No correlation between the source redshift and IDV was found. Also, a correlation between radio flaring & superluminal component ejection and IDV was found. These IDV observations can be qualitatively explained to be arising from the scintillation of compact components dominated by inverse Compton losses. An important distinction was found between the IDV properties of the various blazar subclasses. As expected, less beamed AGN – viz., galaxies and Compact Steep Spectrum/ GigaHertz Peaked Spectrum objects – have been found to be non–IDV sources. Also, almost no genuine BL Lac objects were found to be IDV sources. On the other hand, all intermediate BL Lac/QSO objects (as inferred by the occasional presence of broad lines in their otherwise power-law optical spectra) were found to be IDV sources, with their IDV properties resembling those of quasars. Persistent IDV sources were found to be rare, and with the exception of the high galactic latitude quasar 1156+295, no new rapid IDV source was found.
Degree
Ph.D.
Advisors
Lister, Purdue University.
Subject Area
Astrophysics
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.