Very High Energy Gamma-Ray Astronomy

Very high energy astronomy is relatively new field in astronomy which allows astronomers to gain insight into the most extreme astrophysical processes in our Universe through the observation of very high energy gamma-rays. These very high energy (VHE) photons have energies between 100 GeV and 10 TeV and are produced by violent astrophysical processes or by particles or forces beyond the standard model.

A substantial flux of gamma rays can only be produced via non-thermal processes such as magnetic field or plasma shock in the acceleration of relativistic charged particles.

There have been more than 140 objects detected in the VHE regime. The most common VHE detected object class is that of BL Lac which includes more than 30% of detected objects from total population of VHE gamma-ray. Therefore it is very important to understand their intrinsic properties such as luminosity and spectral variability.

Additionally in observational cosmology a large amount of our knowledge is based on the diffuse background radiation fields surrounding. A prominent example of such a radiation field is the cosmic microwave background (CMB). At shorter wavelengths extragalactic radiation field consists of the accumulated and reprocessed radiation of all starlight produced thus far. This extragalactic background light (EBL) encodes the integrated history of structure formation and the evolution of stars in the Universe. Understanding these characteristics requires detailed theoretical modeling of all contributing processes. VHE gamma-ray emitting BL Lacs (TeV BL Lacs) observations can be used to constrain the amount of EBL indirectly.

Imaging Air Cherenkov Technique (IACT) is being used by ground base pointing telescopes as current technology for VHE gamma-ray detection.

Analyzing each wavelength could guide the scientists to special characters of BL Lacs in the specified wavelength. Whereas, there is another approach to investigation of BL Lacs phenomena by studying different wavelengths and correlation of BL Lacs behavior in different wavelengths for more complete picture.