Abstract Details

Name: Krishna Kumar Singh
Affiliation: Bhabha Atomic Research Centre, Mumbai
Conference ID: ASI2017_755
Title : Very high energy gamma-ray observations of a few Fermi detected blazars using TACTIC telescope
Authors and Co-Authors : .
Abstract Type : Thesis
Abstract Category : Thesis
Abstract : Very High Energy (VHE : E > 100 GeV) gamma-ray observations provide a powerful and unique diagnostic tool for probing a wide variety of cosmic objects within and outside our galaxy. Study of this radiation can yield valuable information about the unusual astrophysical environments characterizing these sources, as well as on the intervening intergalactic space. At energies above 100 GeV, a typical gamma-ray source is generally very weak for detection using space based satellite detectors and thus ground based atmospheric Cherenkov technique is used. As an important part of the on-going global effort to observe VHE gamma-rays from astrophysical sources, scientists from Astrophysical Sciences Division, Bhabha Atomic Research Centre, Mumbai, India, have been actively involved in the observational study of potential gamma-ray sources with the TACTIC (TeV Atmospheric Cherenkov Telescope with Imaging Camera) gamma-ray telescope. With a 5σ sensitivity in 25 hours (before upgrade) for detecting the steady gamma-ray signal from the Crab Nebula above a threshold energy of 1 TeV, the telescope has detected TeV gamma-ray emission from Mrk 421 and Mrk 501 on several occasions during their strong flaring activity. The research work presented in the thesis involves VHE gamma-ray observations of two blazars Mrk 421 and 1ES 1218+304 using TACTIC along with high energy observations from Fermi-LAT (Large Area Telescope) and other instruments in X-ray, optical and radio energy bands. Blazars are the most enigmatic class of active galactic nuclei (AGN), which host a jet closely oriented to the line of sight of the observer on the Earth. The observational results of these two sources are discussed in the context of multi-wavelength emission from blazars and are used to understand the emission model involving synchrotron and synchrotron self Compton (SSC) processes. The thesis also discusses the application of VHE gamma-ray observations of distant blazars for probing the extragalactic background light (EBL), which is an important cosmological quantity for understanding star formation and evolution of galaxies in the Universe.