Probing the Structure of NGC 6814: Spectral and Timing Studies in a Lamp–Post Geometry Framework

The angular size of active galactic nuclei (AGNs) is extremely small, making direct spatial resolution challenging with current facilities. Consequently, indirect techniques such as ‘broadband spectroscopy’ and ‘reverberation mapping’ are crucial for probing the structure and kinematics of AGN components. We conducted a comprehensive spectral and timing analysis of the type 1.5 Seyfert galaxy NGC 6814 using AstroSat (2019) and XMM–Newton (2021) observations. Cross–correlation analysis revealed significant correlations between the X–ray and FUV (λ_mean = 1541 Å, ∆λ = 380 Å) as well as X–ray and UVW1 (λ_mean = 2910 Å, ∆λ = 830 Å) band variations, with time delays of ∼ 15 ks and ∼ 30 ks, respectively. To study the broadband spectral energy distribution (SED), we constructed four SEDs by applying aperture corrections, subtracting host galaxy and emission line contributions, and combining mean X–ray spectra with selected UV data. The SEDs were fitted using the KYNSED model, exploring various inclination angles (θ), black hole spins (a), and color correction factors (f_col). The best–fit results were obtained for θ = 70 and a ≤ 0.5, indicating that 10–20% of accretion power may get transferred to the corona. The corona was found to have a radius of ∼ 6 − 10 r_g and a height of ∼ 7.5 − 35 r_g. The model predicted time–lags closely matched observed values. Our findings strongly support the hypothesis of X–ray illumination of the accretion disk in a lamp–post geometry, without requiring an inner or outer truncated disk. This work highlights how broadband spectroscopy and timing can constrain AGN corona–disk interactions and physical parameters.