Abstract:
Blazars are the radio-loud AGNs with polarized, highly luminous and rapidly variable non-thermal continuum emission ranging from radio to ??rays, from a relativistic jet. These features are interpreted in terms of the synchrotron radiation produced in the jet and beamed in the direction close to the line of sight ! Thus, the study of blazars provides an opportunity to understand the mechanism of energy extraction from the central black hole where jets are formed. A multi-wavelength study of variability is the only way to obtain information on the geometry of the jets and to constrain the parameters characterizing the spectral energy distribution (SED). Radio through ?-ray SED of blazars exhibits two broad humps- first at UV/optical and second one extending from X-ray to ?-rays whose origin is less understood. Variability in blazars has been studied in a number of objects using satellite borne detectors in X, UV and ?-ray bands, sometimes co-ordinated with ground based observations in optical, IR and radio. The variability time scales obtained vary from minutes to years. Such studies wil be reviewed and the emerging scenario will be discussed.
