2025/05/26 by Piyali Ganguly, Ganguly, Piyali, G. C. Dewangan +1
Physics and Astronomy · Engineering · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astronomical Observations and Instrumentation
paper · pdf · doi:10.48550/arxiv.2505.20173
We present a broadband UV/X-ray spectral study of two Seyfert 1 galaxies, Mrk 813 and RBS 688, primarily based on AstroSat observations. These active galactic nuclei host relatively large super-massive black holes (MBH ∼ 108 - 109M\odot), suffer negligible internal extinction/absorption, and are well suited for probing the inner regions of their accretion disks using far UV and soft X-ray spectra. In the case of Mrk 813, the AstroSat and HST far UV spectra are steeper than those expected from a standard accretion disk; the deficit of emission at shorter wavelengths suggests a truncated accretion disk with an inner radius rin ∼ 70rg. Joint UV/X-ray broadband spectral modelling with FAGNSED and RELAGN models suggests that the apparent truncation in Mrk 813 is most likely due to the presence of a warm Comptonising disk in the inner regions that is responsible for the observed soft X-ray excess emission. RBS 688 lacks the soft X-ray excess emission, and the UV data are entirely consistent with a standard disk that appears to extend very close to the innermost stable circular orbit. Our study suggests the formation of the warm, optically-thick Comptonising corona in the innermost disk regions at higher Eddington fraction.