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SCIENTIFIC
RATIONALE
Investigation
of nature of the emitting ionized gas in galactic nuclei is one of important
subjects in astrophysics today. Firstly, investigating the processes in the
central parts of these objects, we can learn about the innermost parts of
other 'normal' galaxies. Secondly, AGN are the most powerful sources,
located at different cosmological time-scales, and their investigation is
cosmologically important. Finally, a part of emission from these objects
(e.g. in the X-rays) has its origin very close to a massive black hole, and
investigation of this emission can help us understand the physical processes
in a strong gravitational field. On the other side, a number of AGN are
affected by gravitational lensing effect.
Gravitational
lensing is in general achromatic: the deflection angle of a light ray does
not depend on its wavelength. However, the wavelength-dependent geometry of
the various emission regions may result in chromatic effect. Studies aimed
at determining the influence of microlensing on spectra of lensed quasars
(hereafter QSOs) ought to account for the complex structure of the QSO
central emitting region. Since the sizes of the emitting regions are
wavelength-dependent, microlensing by stars in a lens galaxy will lead to a
wavelength-dependent magnification.
Many
interesting details about the physics of processes that are taking place
within AGN can be identified in the signal of their emitting regions (as
e.g. Broad Line Region - BLR), but they suffer from a still missing complete
picture of the complex kinematical and thermodynamical properties of the
line emitting plasma. Since it is not yet possible to directly observe the
spatial distribution of the broad line emitting medium, although many
important achievements were obtained in the angular resolution of AGN cores
at radio wavelengths, spectroscopic data are still the most useful way to
investigate physics within the central part of an AGN.
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