A systematic study of the optical to X-ray spectral properties of active galactic nuclei

In this thesis I present a detailed study of the optical to X-ray spectral properties of Active Galactic Nuclei (AGN). We propose a new broadband SED model which combines the standard accretion disc emission, low and high temperature Comptonisation components by introducing a corona radius. Applying the new models to broadband spectral data, we found that RX J0136.9-3510 and RE J0134+396 have similar {\it rms} spectra and broadband SEDs, representing a distinct spectral state which can only be attained by super Eddington flows. A detailed optical and X-ray spectral analysis is then carried out for a big sample of 51 unobscured nearby type 1 AGNs. We find that NLS1s tend to have softer 2-10 keV spectra, lower black hole mass, higher Eddington ratio, higher $\alpha_{ox}$ index and smaller coronal radius. The edge of Balmer continuum is shifted redwards and smoothed by more than predicted by the FWHM of the Balmer emission lines. A new method called `Correlation Spectra Technique (CST)' is proposed, which is powerful for multi-waveband spectral analysis. We find that among the three Balmer line components, the broad component has the best correlation with hard X-ray emission. Optical oxygen forbidden lines all well correlate with the hard X-ray emission. We conducted a systematic cross-correlation among the 9 key SED parameters: $\Gamma_{2-10keV}$, $\kappa_{2-10keV}$, $\kappa_{5100A}$, $\lambda_{Edd}$, FWHM$_{H\beta}$, M$_{BH}$, $\alpha_{ox}$, L$_{bol}$ and L$_{2-10keV}$, and found the driven parameters to be M$_{BH}$, $\lambda_{Edd}$ and L$_{bol}$ (or equivalently $\dot{M}$). AGN's intrinsic SEDs exhibit strong diversity and changes similarly with $\lambda_{Edd}$, $\kappa_{2-10keV}$, $\kappa_{5100}$, $\Gamma_{2-10keV}$, FWHM$_{H\beta}$ and M$_{BH}$. However, the SED shape is not sensitive to L$_{bol}$.EThOS - Electronic Theses Online ServiceGBUnited Kingdo