Philip A. Hughes

The University of Michigan radio astronomy data base. I. Structure function analysis and the relation between BL Lacertae objects and quasi-stellar objects

A structure function analysis on a well-observed group of variable extragalactic sources, monitored in total and polarized flux in the centimeter waveband since 1965, has been performed. Total flux structure functions of BL Lac objects and QSOs exhibit very similar power-law slopes, suggesting that the same processes are responsible for the variability in both types of source. In view of the recent success of the shocked-jet model for radio source variability, it is argued that the current work provides circumstantial evidence for the ubiquity of such shocked flows

Multiepoch multiwavelength spectra and models for blazar 3C 279

Of the blazars detected by EGRET in GeV γ-rays, 3C 279 is not only the best observed by EGRET but also one of the best monitored at lower frequencies. We have assembled 11 spectra, from GHz radio through GeV γ-rays, from the time intervals of EGRET observations. Although some of the data have appeared in previous publications, most are new, including data taken during the high states in early 1999 and early 2000. All of the spectra show substantial γ-ray contribution to the total luminosity of the object; in a high state, the γ-ray luminosity dominates over that at all other frequencies by a factor of more than 10. There is no clear pattern of time correlation; different bands do not always rise and fall together, even in the optical, X-ray, and γ-ray bands. The spectra are modeled using a leptonic jet, with combined synchrotron self-Compton plus external Compton γ-ray production. Spectral variability of 3C 279 is consistent with variations of the bulk Lorentz factor of the jet, accompanied by changes in the spectral shape of the electron distribution. Our modeling results are consistent with the UV spectrum of 3C 279 being dominated by accretion disk radiation during times of low γ-ray intensity.

Simulations of relativistic extragalactic jets

We describe a method for the numerical solution of the relativistic Euler equations which we have found to be both robust and efficient, and which has enabled us to simulate relativistic jets. The technique employs a solver of the Godunov-type, with approximate solution of the local Riemann problems, applied to laboratory frame variables. Lorentz transformations provide the rest frame quantities needed for the estimation of wave speeds, etc. This is applied within the framework of an adaptive mesh refinement algorithm, allowing us to perform high-resolution, 2-D simulations with modest computing resources. We present the results of nonrelativistic, and relativistic (

Radio Monitoring of OJ 287 and Binary Black Hole Models for Periodic Outbursts

\gamma=5

Centimeter-Wavelength Total Flux and Linear Polarization Properties of Radio-loud BL Lacertae Objects

and

Pearson-readhead survey sources: properties of the centimeter-wavelength flux and polarization of a complete radio sample

10

Pearson-Readhead Survey Sources. II. The Long-Term Centimeter-Band Total Flux and Linear Polarization Properties of a Complete Radio Sample

) runs, for adiabatic indices of

Parsec-Scale Blazar Monitoring: Flux and Polarization Variability

5/3

A Comparison of the Morphology and Stability of Relativistic and Nonrelativistic Jets

and

Multiwavelength monitoring of the BL Lacertae object PKS 2155-304. 4: Multiwavelength analysis

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