Taking a survey and analysing the X-Ray spectra of Dual AGNs

Active Galactic Nuclei

The centre of galaxy usually harbours a Super Massive Black Hole (SMBH), which forms the deepest potential of the galactic system. This SMBH essentially creates the trapping potential for the Galactic system to sustain itself and not fly out.
The mass of a SMBH varies from nearly millions to billions time the solar mass. Some of these nuclei are highly luminous, and cannot be explained by stellar population. Such nuclei are called Active Galactic Nuclei. They emit radiation in all wavelengths. These have been detected in a major fraction of the elliptical and spiral galaxies.
AGNs are basically accreting SMBHs. Gases and dust swirl around the black hole, forming an accretion disk. In the inner circle of the accretion disk, mass is absorbedinto the black hole, while a part of it is released as radiation and highly energetic matter. The radiation from the accretion from the closest stable orbit, gives us infomation about the near event horizon environment.
The presence of molecular torii around the central machinery causes very strong absorption lines to appear in the corresponding spectrum. An accretion disk is formed, when matter with non-zero angular momentum falls into the gravitational potential, and looses energy as it swirls around the SMBH, finally accreting into the Black Hole.The process of accretion is an efficient process in the re- lease of radiation. The energy release in this process can be approximated to first order, by the change in potential energy $(\Delta E)$ of a test particle of mass $m$, in the gravitational eld of the black hole, falling into it.

Where, $R_{S}$ is the Schwarzschild radius of the black hole.

The accretion Luminosity $(L_{A})$, which is luminosity of the corresponding radiation from an accreting system.

Where $\zeta$ is related to the efficiency of the Accretion process.

Estimating geometry from Spectra

As gas and matter accretes on to the black hole, from the last stable orbit around it, a part of matter is ejected as energy or highly energetic beam of matter. This causes the emission of high energy radiation in X-Rays, gamma rays, etc. Some part of this radiation often is reflected, absorbed and re-emitted, and appears as spectral features over the X-ray continuum, which follows a power law. If we can pick up models, to fit this spectra, and fit to obtain specific parameters, we can extract information regarding the near event horizon geometry. Using tools like Chandra SHERPA, or NASA HEASOFT, one can constrain parameters that describe the geometry, simply by picking one of the models, and fitting the corresponding spectra. There are speculations regarding which model suits best for the purpose and explains the physics properly, we can pick up different models and constrain the geometry for each of the case.