Recent years have seen a tremendous progress in field of the high energy ( HE ) astrophysics and very high energy ( VHE ) astronomy .
This progress has been achieved mostly thanks to a new generation of instruments that provide data of previously unattainable quality .
This thesis presents the study of four aspects of high energy astronomy .

The first part of my 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 . ) .
H.E.S.S .
is an array dedicated to VHE \gamma -ray astronomy .
The array has been in operation since the beginning of 2004 .
Originally it has been composed of four 12 meter diameter telescopes , which has been completed with a fifth 28 meter diameter telescope in 2012 .
This H.E.S.S .
II telescope is designed to operate both in stereoscopic mode and in monoscopic mode .
The Level 2 trigger system is required to suppress spurious triggers of the telescope when operating in monoscopic mode .
This dissertation provides the motivation and principle of the operation of the Level 2 trigger .
I had the opportunity to work on the Level 2 trigger system for the H.E.S.S .
II telescope at IRFU/CEA in France .
The IRFU is responsible for designing and building this trigger system .
The system consists of both hardware and software solutions .
My work on the project focused on the algorithm development and the Monte Carlo simulations of the trigger system and overall instrument ( Moudden , Barnacka , Glicenstein et al .
2011a ; Moudden , Venault , Barnacka et al .
2011b ) .
The hardware implementation of the system is described and its expected performances are then evaluated .

The H.E.S.S .
array has been used to observe the blazar PKS 1510-089 .
The second part of my thesis deals with the data analysis and modeling of broad-band emission of this particular blazar .
PKS 1501-089 is an example of the so-called flat spectrum radio quasars ( FSRQs ) for which no VHE emission is expected due to the Klein-Nishina effects and strong absorption in the broad line region ( Moderski et al .
2005 ) .
The recent detection of at least three FSRQs by Cherenkov telescopes has forced a revision of our understanding of these objects .
In part II of my thesis , I am presenting the analysis of the H.E.S.S .
data : the light curve and spectrum of PKS 1510-089 , 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 model is based on a single zone internal shock scenario .

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 .
Traditional methods for the estimation of time delays in gravitational lensing systems rely on the cross-correlation of the light curves from individual images .
In my thesis , I used 300 MeV-30 GeV photons detected by the Fermi-LAT instrument .
The FERMI-LAT instrument can not separate the images of known lenses .
The observed light curve is thus the superposition of individual image light curves .
The FERMI-LAT instrument has the advantage of providing long , evenly spaced , time series with very low photon noise .
This allows to use directly Fourier transform methods .

A time delay between the two compact images of PKS 1830-211 has been searched for both by the autocorrelation method and a new method : the “ double power spectrum ” .
The double power spectrum shows a 4.2 \sigma evidence for a time delay of 27.1 \pm 0.6 days ( Barnacka et al .
2011 ) , consistent with the results from Lovell et al .
( 1998 ) and Wiklind & Combes ( 2001 ) .

The last part of my thesis concentrates on another lensing phenomena called ” femtolensing ” .
The search for femtolensing effects has been used to derive limits on the primordial black holes abundance .
The abundance of primordial black holes is currently significantly constrained in a wide range of masses .
The weakest limits are established for the small mass objects , where the small intensity of the associated physical phenomenon provides a challenge for current experiments .
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 .
The lack of femtolensing detection in the GBM data provides new evidence that primordial black holes in the mass range 5 \times 10 ^ { 17 } – 10 ^ { 20 } g do not constitute a major fraction of dark matter ( Barnacka et al .
2012 ) .

My Ph.D. studies have been carried out jointly between the Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences , in Warsaw in Poland and the IRFU institute of the Commissariat á l ’ énergie atomique et aux énergies alternatives ( CEA ) Saclay in France .