Microvariability in Blazars

Optically violent variable quasars and BL Lac objects, which form a subclass of active galactic nuclei are termed as Blazars. Blazars show high degree variation in their flux and polarization in a relatively shorter period of time. They are strong radio sources with a non-stellar continuum. Most of the BL Lac objects do not show any emission lines though in some cases very weak lines are observed. They harbour in elliptical galaxies. Some BL Lacs show superluminal motion indicating the flow of matter at relativistic speeds close to the line of sight. It is likely that the enormous energy produced by these objects may be due to a massive black hole with an accretion disc system. Some Blazars have been observed to detect short time variations in their flux and polarization in the visual band. These studies are aimed at understanding the physical processes taking place in the central engine. Detecting shorter period variations assumes significance as they impose restrictions on the total volume from where the huge amount of energy is comming out. To date the recorded shortest period variation in visual band is 6.3 min in OJ 287, a BL Lac object. Attempts are being made to detect shorter period variations, which pose observational challenges. It is generally accepted that the central engine of AGN harbours a massive blackhole with an accretion disc surrounding it. This revised version was published online in July 2006 with corrections to the Cover Date.