  This thesis presents the study of four aspects of high energy astronomy. The
first part of the thesis is dedicated to an aspect of instrument development
for imaging atmospheric Cherenkov telescopes, namely the Level 2 trigger system
of the High Energy Stereoscopic System (H.E.S.S.). I am providing the
motivation and principle of the operation of the Level 2 trigger, I am
describing hardware implementation of the system and then I am evaluating
expected performances. The second part of my thesis deals with the data
analysis and modeling of broad-band emission of particular blazar PKS 1510-089.
I am presenting the analysis of the H.E.S.S. data, together with the FERMI data
and a collection of multi-wavelength data obtained with various instruments. I
am presenting the model of PKS 1510-089 observations carried out during a flare
recorded by H.E.S.S.. The third part of my thesis deals with blazars observed
by the FERMI-LAT, but from the point of view of other phenomena: a strong
gravitational lensing. This part of my thesis shows the first evidence for
gravitational lensing phenomena in high energy gamma-rays. This evidence comes
from the observation of a gravitational lens system induced echo in the light
curve of the distant blazar PKS 1830-211. The last part concentrates on another
lensing phenomena called femtolensing. The search for femtolensing effects has
been used to derive limits on the primordial black holes abundance. I have used
gamma-ray bursts with known redshifts detected by the FERMI Gamma-ray Burst
Monitor (GBM) to search for the femtolensing effects caused by compact objects.
