Multi-wavelength studies of active galactic nuclei

Abstract

Blazars comprise a subclass of radio loud Active Galactic Nuclei (AGN) that consist of BL Lacertae objects (BL Lacs) and Flat Spectrum Radio Quasars (FSRQs). They display large amplitude flux and polarization variability on diverse time-scales across the entire electromagnetic (EM) spectrum. According to the current paradigm, blazars have a Super Massive Black Holes (SMBHs) at their centre that accretes matter and produce relativistic jets pointing almost in the direction of our line of sight. The emission from blazars is predominated by non-thermal radiation produced by relativistic electrons spiralling around the magnetic field in relativistic jets. The spectral energy distributions (SEDs)of the blazars have two humps in log(νF ) vs log(ν) representation. The low energy SED hump peaks in the frequency ranging from sub-mm to soft X-ray bands and is well explained by synchrotron emission from an ultra-relativistic electron population residing in the magnetic field of the approaching relativistic jet. The high energy SED hump that peaks in MeV–TeV γ−ray bands, is usually attributed to inverse Compton (IC) scattering of photons of those relativistic electrons.