Abstract Details

Name: Atreyee Sinha
Affiliation: IUCAA
Conference ID: ASI2017_1138
Title : A Multiwavelength Study of TeV Blazars
Authors and Co-Authors : Under Prof. V. R. Chitinis, TIFR, Mumbai
Abstract Type : Thesis
Abstract Category : Thesis
Abstract : Blazars constitute the most violent non-transient sources of high energy emission in the known universe and are ideal for studying the physics of poorly understood astrophysical jets. Though blazars emit copiously across the entire electromagnetic spectrum, the origin of the high energy emission is still under debate. The jet formation, collimation and acceleration are still only vaguely understood. The observed rapid variability suggests that the emission region is compact and located close to the nucleus, which lies below the resolution limit of modern facilities. Thus, even the sites of production of radiation at different energies are also not well known. The advent of the Atmospheric Cherenkov Telescopes (ACT) opened a new window into blazar research. Since the atmosphere is opaque to TeV photons, a direct detection id not possible. However, the energy and arrival direction of the  primary TeV photon can  be reconstructed from the Cherenkov light pool created by the Extensive Air Showers. This requires state of the art detection techniques and Monte-Carlo simulations. Moreover, studies at TeV energies are complicated due to the fact that the high energy gamma rays emitted from blazars interact with the Extragalactic Background Light (EBL) through pair production and are attenuated. Until now, several different models of the EBL have been proposed, which differ considerably. Very high energy emission seen from blazars has proven to be a very good test for these EBL models. In such a scenario, multi-wavelength temporal and spectral studies offer powerful diagnostics to study the underlying blazar environment. We analyse data from the TeV Telescope Array, HAGAR, located in the Ladakh Valley of the Himalayan Mountain Ranges, along with data from the Fermi-LAT, NuSTAR and Swift Telescopes to to understand the intrinsic particle spectrum in the jets through a thorough temporal and spatial study of HAGAR observed blazars in the ambit of leptonic models. The primary goal of this thesis has been to study the radiation mechanisms in blazar jets, with emphasis on the high energy emission. We have developed a synchrotron - Inverse Compton minimisation routine in XSPEC, and used it to study the broadband (radio - γ-ray) spectral and temporal emission from two blazars, Mkn 421 and 1ES 1011+496, and tried to understand its implications under the ambit of leptonic modelling. A model independent estimate of the EBL has been computed from a statistical study of TeV detected blazars. The results of the work will be presented and some future prospects discussed.