Investigation of the obscuring torus in AGN using multi-wavelength SED

The PhD thesis is focused on characterizing the properties of the obscuring torus in active galactic nuclei (AGN) by analyzing X-ray and multi-wavelength spectral energy distributions. The torus, consisting of molecular and dusty clouds, is believed to cause nuclear obscuration. However, its exact properties remain uncertain. AGN emit diffuse X-ray radiation, contributing significantly to the cosmic X-ray background (CXB), with Compton-thick AGN (CT-AGN) being major contributors around its peak energy. Despite this, observations reveal a discrepancy with AGN population synthesis models, indicating a need for a comprehensive census of obscured AGN at various wavelengths. In the first part of my thesis, I conducted X-ray spectral analysis on seven heavily obscured AGN candidates in the local Universe. Utilizing data from Chandra, XMM-Newton, and NuSTAR, I examined torus properties using advanced X-ray torus models. Results identified three bona fide CT-AGN and three Compton-Thin AGN. Notably, one source was found to be less obscured than previously thought, underscoring the importance of reliable constraint methods. Combining this analysis with previous studies, only a small fraction of AGN are CT-AGN, contrary to model predictions. In the second part, I focused on NGC 6300, a changing-look AGN candidate, conducting comprehensive X-ray spectroscopic analysis using advanced torus models. Results revealed no variability in line-of-sight column density but showed intrinsic flux variability. Additionally, evidence of an inner CT-ring of gas was found, contributing to reflection-dominated spectra. Optical to far-infrared band fluxes were extracted for broad-band spectral energy distribution fitting, allowing investigation of torus geometry and host galaxy properties. Overall, this research provides valuable insights into the properties and behavior of heavily obscured AGN and contributes to our understanding of the nature of the obscuring torus in AGN.