Related papers: Intergalactic $\gamma$-ray propagation: basic idea…
Gamma rays from distant blazars interact with the extragalactic background light, creating electron-positron pairs, and reducing the gamma-ray flux measured by ground-based atmospheric Cherenkov gamma-ray telescopes. These pairs can…
Flux distribution is an important tool to understand the variability processes in active galactic nuclei. We now have available a great deal of observational evidences pointing towards the presence of log-normal components in the high…
Variable $\gamma$-ray flares upto minute timescales reflect extreme particle acceleration sites. However, for high-redshift blazars, the detection of such rapid variations remains limited by current telescope sensitivities. Gravitationally…
Blazars are the most common sources of $\gamma$-ray photons in the extragalactic sky. Their $\gamma$-ray light curves are characterized by bright flaring episodes, similarly to what is observed at longer wavelengths. These gamma-ray bursts…
Various studies have implied the existence of a gaseous halo around the Galaxy extending out to 100 kpc. Galactic cosmic rays (CRs) that propagate to the halo, either by diffusion or by convection with the possibly existing large-scale…
Observations of the gamma-ray sky reveal the most powerful sources and the most violent events in the Universe. While at lower wavebands the observed emission is generally dominated by thermal processes, the gamma-ray sky provides us with a…
Blazars, a subset of powerful active galactic nuclei, feature relativistic jets that shine in a broadband electromagnetic radiation, e. g. from radio to TeV emission. Here I present the results of the studies that explore gamma-ray and…
In the first 3.5 years of operations the Fermi LAT detected several sources with daily fluxes brighter than F(E>100MeV) > 10^{-6} ph/cm^2/s, the threshold set by the Fermi Collaboration for issuing an Astronomer Telegram. We focus the…
Microquasars are potential candidates to produce a non-negligible fraction of the observed galactic cosmic rays. The protons accelerated at the jet termination shock interact with the interstellar medium and may produce detectable fluxes of…
Extreme scattering events (ESEs) are distinctive fluctuations in the brightness of astronomical radio sources caused by occulting plasma lenses in the interstellar medium. The inferred plasma pressures of the lenses are $\sim 10^3$ times…
The origin and nature of ultrahigh energy cosmic rays with energies above $10^{20}\,$eV is a puzzle for the physics and astrophysics of cosmic rays which is still unresolved. In this paper, I report on an extensive study on the propagation…
Active galactic nuclei (AGN) with jets seen at small viewing angles are the most luminous and abundant objects in the $\gamma$-ray sky. AGN with jets misaligned along the line-of-sight appear fainter in the sky, but are more numerous than…
We re-derive the possible dependence of the redshift with very high energy (VHE) $\gamma$-ray photon index. The results suggest that the universe to VHE $\gamma$-rays is becoming more transparent than usually expected. We introduce the…
Gamma-ray observations ranging from hundreds of MeV to tens of TeV are a valuable tool for studying particle acceleration and diffusion within our galaxy. Supernova remnants, pulsar wind nebulae, and star-forming regions are the main…
A large distance propagation in turbulent atmosphere results in disintegration of laser beam into speckles. We find that the most intense speckle approximately preserves both the Gaussian shape and the diameter of the initial collimated…
The extragalactic background light (EBL) from the infrared to the ultraviolet is difficult to measure directly, but can be constrained with a variety of methods. EBL photons absorb gamma-rays from distant blazars, allowing one to use blazar…
Recent observations of blazars at high energy (HE, 0.1-100 GeV) and very high energy (VHE, >0.1 TeV) have provided important constraints on the intensity and spectrum of the diffuse Extragalactic Background Light (EBL), shedding light on…
A Monte Carlo program for the simulation of electromagnetic cascades initiated by high-energy photons and electrons interacting with extragalactic background light (EBL) is presented. Pair production and inverse Compton scattering on EBL…
Gamma-ray blazars are among the most extreme astrophysical sources, harboring phenomena far more energetic than those attainable by terrestrial accelerators. These galaxies are understood to be active galactic nuclei that are powered by…
Galactic cosmic rays are commonly believed to be accelerated at supernova remnants via diffusive shock acceleration. Despite the popularity of this idea, a conclusive proof for its validity is still missing. Gamma-ray astronomy provides us…