Related papers: The Extragalactic Diffuse Gamma-Ray Emission
The diffuse Galactic gamma-ray flux between 0.1 and 1 PeV has recently been measured by the Tibet AS$\gamma$ Collaboration. The flux and spectrum are consistent with the decay of neutral pions from hadronuclear interactions between Galactic…
The gamma-ray energy range from a few hundred keV to a few hundred MeV has remained largely unexplored, mainly due to the challenging nature of the measurements, since the pi- oneering, but limited, observations by COMPTEL on the Compton…
The pair-production absorption of high-energy gamma-rays by intergalactic low-energy photons is expected to produce a high-energy cutoff in the spectra of extragalactic sources which is a sensitive function of redshift. We first discuss the…
We investigate the GeV emission from gamma-ray bursts (GRBs), using the results from the Energetic Gamma Ray Experimental Telescope (EGRET), and in view of the Gamma-ray Large Area Space Telescope (GLAST). Assuming that the conventional…
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…
The "GeV-excess" of the diffuse gamma-rays in the halo is studied with a template fit based on energy spectra for each possible process of gamma-ray emission. Such a fit allows to determine the background and signal simultaneously, so the…
Ultra-high energy cosmic ray protons accelerated in astrophysical objects produce secondary electromagnetic cascades during propagation in the cosmic microwave and infrared backgrounds. We show that such cascades can contribute between ~1%…
An intergalactic magnetic field stronger than $3\times10^{-13}$~G would explain the lack of a bright, extended degree-scale, GeV-energy inverse Compton component in the gamma-ray spectra of TeV-blazars. A robustly predicted consequence of…
Pulsed emission from gamma-ray pulsars originates inside the magnetosphere, from radiation by charged particles accelerated near the magnetic poles or in the outer gaps. In polar cap models, the high energy spectrum is cut off by magnetic…
The Large High-Altitude Air Shower Observatory (LHAASO) recently published measurements of diffuse Galactic gamma-ray emission (DGE) in the 10-1000 TeV energy range. The measured DGE flux is significantly higher than the expectation from…
The Galactic background radiation near the Scutum Arm was observed simultaneously with RXTE and OSSE in order to determine the spectral shape and the origin of the emission in the hard X-ray/soft gamma-ray band. The spectrum in the 3 keV to…
The diffuse galactic EGRET gamma ray data show a clear excess for energies above 1 GeV in comparison with the expectations from conventional galactic models. The excess is seen with the same spectrum in all sky directions, as expected for…
Recent results from experiments like PAMELA have pointed to excesses of e+e- in cosmic rays. If interpreted in terms of Dark Matter annihilations, they imply the existence of an abundant population of e+e- in the galactic halo at large. We…
Primary gamma rays emitted by extragalactic sources, such as blazars, will generate electromagnetic cascades in intergalactic space. These cascades proceed via electron-positron pair production and inverse Compton scattering on cosmic…
Very high-energy gamma-rays (VHE, E>100 GeV) propagating over cosmological distances can interact with the low-energy photons of the extragalactic background light (EBL) and produce electron-positron pairs. The transparency of the universe…
The Fermi Gamma-ray Observatory discovered about a thousand extragalactic sources emitting energy from 100 MeV to 100 GeV. The majority of these sources belong to the class of blazars characterized by a quasi-featureless optical spectrum…
At TeV energies, the gamma-ray horizon of the universe is limited to redshifts z<<1, and, therefore, any observation of TeV radiation from a source located beyond z=1 would call for a revision of the standard paradigm. While robust…
We present an upper limit of galactic diffuse gamma-ray flux, measured with the GAMMA experiment at energy about 175 TeV. The results were obtained using selection of muon poor extensive air showers at mountain level (700 g/cm^2, Mt.…
The diffuse extragalactic background light consists of the sum of the starlight emitted by galaxies through the history of the Universe, and it could also have an important contribution from the first stars, which may have formed before…
Air shower experiments have detected cosmic ray events of energies upto 300 EeV. Most likely these cosmic rays have originated from compact objects. Their exact sources are yet to be identified. It has been suggested before that gamma ray…