相关论文: Blazar Gamma-Rays, Shock Acceleration, and the Ext…
The extragalactic high-energy $\gamma$-ray sky is dominated by blazars, which are active galactic nuclei with their jets pointing towards us. Distance measurements are of fundamental importance yet for some of these sources are challenging…
The interaction of TeV photons from blazars with the extragalactic background light produces a relativistic beam of electron-positron pairs streaming through the intergalactic medium (IGM). The fate of the beam energy is uncertain. By means…
TeV gamma rays from distant astrophysical sources are attenuated due to electron-positron pair creation by interacting with ultraviolet/optical to infrared photons which fill the universe and are collectively known as the extra-galactic…
The production site of gamma rays in blazars is closely related to their interaction with the photon fields surrounding the active galactic nucleus. In this work we discuss an indirect method that may help to unveil the presence of ambient…
The discovery of distant sources of very high energy (VHE) gamma-rays with hard energy spectra enabled to derive strong upper limits on the density of the extragalactic background light (EBL). These limits are close to the lower limits…
Blazars radiate from relativistic plasma jets with bulk Lorentz factors {\Gamma} ~ 10, closely aligned along our line of sight. In a number of blazars of the Flat Spectrum Radio Quasar type such as 3C 454.3 and 3C 279 gamma-ray flares have…
The development of instabilities leading to the formation of internal shocks is expected in the relativistic outflows of both gamma-ray bursts and blazars. The shocks heat the expanding ejecta, generate a tangled magnetic field and…
Origin of extragalactic gamma-ray background (EGRB) is still a matter of debate. EGRB can either have truly diffuse or unresolved discrete point sources origin. Majority of the Fermi and EGRET detected identified sources are blazar. So,…
We combine the recent estimate of the contribution of galaxies to the 3.6 micron intensity of the extragalactic background light (EBL) with optical and near-infrared (IR) galaxy counts to set new limits on intrinsic spectra of some of the…
The distribution of TeV spectral slopes versus redshift for currently known TeV blazars (16 sources with z<0.21, and one with z>0.25) is essentially a scatter plot with hardly any hint of a global trend. We suggest that this is the outcome…
Recent findings by gamma-ray Cherenkov telescopes suggest a higher transparency of the Universe to very-high-energy (VHE) photons than expected from current models of the Extragalactic Background Light. It has been shown that such…
Blazars are the most plentiful gamma-ray source at GeV energies, and despite detailed study, there is much that is not known about these sources. In this review I explore some recent results on blazars, including the controversy of the…
As very-high--energy photons propagate through the extragalactic background light (EBL), they interact with the soft photons and initiate electromagnetic cascades of lower energy photons and electrons. The collective intensity of a…
Three independent predictions follow from postulating the existence of protons co-accelerated with electrons in extragalactic jets (i) multi-TeV gamma ray emission from nearby blazars, (ii) extragalactic cosmic ray protons up to 10^20 eV,…
Relativistic jets from accreting supermassive black holes at cosmological distances can be powerful emitters of $\gamma$-rays. However, the precise mechanisms and locations responsible for the dissipation of energy within these jets,…
Blazars are a sub-category of radio-loud active galactic nuclei with relativistic jets pointing towards to the observer. They are well-known for their non-thermal variable emission, which practically extends over the whole electromagnetic…
TeV gamma rays emitted by GRBs are converted into electron-positron pairs via interactions with the extragalactic infrared radiation fields. In turn the pairs produced, whose trajectories are randomized by magnetic fields, will inverse…
Recent observations with the low threshold Cherenkov telescopes proved that sub-TeV gamma-rays are able to arrive from active galaxies at relatively large distances in spite of expected severe absorption in the extragalactic background…
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…
Collecting experimental insight into the relativistic particle populations and emission mechanisms at work within TeV-emitting blazar jets, which are spatially unresolvable in most bands and have strong beaming factors, is a daunting task.…