Blazars

Watcher is used to monitor many other sources when no GRB is being actively observed, including variable stars and Active Galactic Nuclei (AGN). The subset of AGN known as blazars has recently become the focus of a monitoring campaign designed to probe the variability timescales in these AGN by providing both short-term and long-term optical variability data for key southern hemisphere sources.

Sketch of the basic ideas of the unified AGN model. Credit: Beckmann & Shrader (2012).

Sketch of the basic ideas of the unified AGN model. Credit: Beckmann & Shrader (2012).

Blazars are compact astrophysical sources, believed to be powered by the accretion of material onto a supermassive black hole at the centre of an active, giant elliptical galaxy. Key defining characteristics of blazars include their rapid variability at all wavelengths and their high luminosities, both characteristics that may be enhanced by relativistic beaming effects.

Optical studies of blazars are a vital part of the study of these objects due to the fact that the synchrotron peak of the broad spectral energy distribution is often located within this band. Additionally, the relationship between high-energy and optical variability in blazars is complex. The Synchrotron Self Compton (SSC) mechanism can pump up the optical synchrotron photons in the Thomson limit to Fermi-LAT energies. By constraining the optical synchrotron spectrum through multi-wavelength observations, the gamma-ray production capabilities of these sources can be constrained. Dedicated multi-band observations are required to understand:

  1. the nature of the optical variability, which is a de ning characteristic of blazars
  2. the occurrence (or otherwise) of lags between optical and gamma/X-ray flares
  3. colour changes as a function of intensity