Time-domain and Spectral Studies of Fermi-LAT Blazars -- Optical Observations from South Africa-based telescopes and gamma rays

Blazars are known as the most energetic sources of the Universe, apart from gamma-ray bursts. They constitute a specific type of radio-loud active galactic nucleus (AGN), understood as a supermassive black hole surrounded by an accretion disk that powers a pair of twin jets of relativistic plasma, with one of the jets pointing close to the Earth direction. The particles of these jets interact with the surrounding media and radiation fields through shocks. Thus, the radiation from these sources appears dominated by the non-thermal radiation from the jets. Flat spectrum radio quasars (FSRQ) and BL Lac objects are the two main subdivisions of blazars. During its first four year observation period (2008-2012), the Fermi Gamma-Ray Space Telescope identified 1741 AGNs, and reported 1145 blazars and 573 blazar candidates of uncertain type (BCU) in the Third Fermi-LAT Point Source Catalog (3FGL). Data from these sources were analysed at energies > 100 MeV, having redshifts that range from less than 0.1 to more than 3. Since blazar variability can be observed at gamma-ray energies on sub-hour time scales, the Fermi-LAT blazar sample is of particular interest for constraining the sizes and locations of emitting plasma blobs at distances close to the central supermassive black hole. I will present in this seminar our work on FSRQ 3C 454.3 during its June 2016 flare, and our on-going study of FSRQ 4C +01.02, during its long lasting flare of 2016. I will also present our work on the classification of blazars that we undertook through the identification of features in the optical spectra of these objects, and mainly through the strength of their lines. These investigations are undertaken through photometric and spectroscopic observations using South Africa-based telescope, including the 10-m Southern African Large Telescope (SALT) at the South African Astronomical Observatory (SAAO), Sutherland.