Multi-waveband Behavior of Blazars

Abstract

Abstract. The author reviews recent progress toward understanding blazars that multi-waveband monitoring observations have advanced. The primary techniques include the compilation of multi-waveband light curves, multi-epoch VLBI images at radio wavelengths, plots of linear polarization vs. time at radio through optical wavelengths, and spectral energy distributions (SEDs). Correlations and the coincidence or lag of events across wavebands and in the images indicate where the events take place relative to the "core" that lies 0.5 pc from the central engine. Rotations of the polarization electric vector suggest a helical geometry of the magnetic field upstream of the millimeter-wave core, while rapid fluctuations in degree and position angle of polarization imply that the jet plasma is turbulent in and downstream of the core. The author is developing a numerical model that simulates the emission from such turbulence as it interacts with a conical standing shock in the core region.

The Long-Term Centimeter Variability of Active Galactic Nuclei: A New Relation Between Variability Timescale and Accretion Rate*

“…Especially, there is growing evidence for interaction of moving jets with (probably) stationary cores, leading to strong flares at high energies (from optical to γ-rays) and, likewise, at cm/mm wavelengths (Savolainen et al 2002;León-Tavares et al 2010;Arshakian et al 2010). The cm/mm flares show much broader flare widths and time delays relative to the high energy flares, likely due to relatively long cooling timescales and high optical depths (e.g., Savolainen et al 2006;Jorstad et al 2010;Marscher et al 2008Marscher et al , 2010Marscher et al , 2011Marscher 2013). If the core is a conical, standing shock (commonly assumed to be a recollimation shock, see e.g., Cawthorne 2006;Cawthorne et al 2013;Marscher 2006Marscher , 2014, then the duration of flares would be determined by the crossing time of jet material through the shock.…”

A model for periodic blazars

“…Blazars are powerful gamma-ray sources that are believed to consist in a jet powered by an AGN pointing in the general direction of the Earth (see for example Urry & Padovani 1995;Marscher 2013). It is natural to ask whether their jets can precess too and, if so, what is the physical mechanism responsible for the precession.…”

VLBI observations of flared optical quasar CGRaBS J0809+5341

“…Most blazar outbursts are known to occur at pc-scale distances from the central engine, around the radio core region (see e.g. Marscher 2013, for a review). This can be confirmed by long-term monitoring observations with dense time sampling, from radio to γrays, supplemented with high-resolution VLBI monitoring in the radio.…”