Institute for Advanced Study Informal Astrophysics Seminar

There is a great deal of evidence that the defining characteristics of blazars, such as extreme variability across the electromagnetic spectrum and high fractional polarization, are produced by shocks in relativistic jets pointing close our line of sight. Some different techniques that have been employed to estimate the Lorentz factors of these flows will be reviewed before a case for ultrarelativistic flows being present in the subset of blazars known to emit TeV radiation is presented. We have recently found good evidence for transient periodic components of tens of minutes in the optical emission from S5 0716+714 as well as periodic components in x-ray emission of ~17 days for AO 0235+164 and of ~420 days for 1ES 2321+419. The most likely origins of such variability components will be suggested.