Related papers: Diffuse gamma-rays from galactic halos
One of the unsolved problems in cosmic ray (CR) physics is the small radial gradient of the gamma-ray intensity compared to the inferred CR source distribution in the Galactic disk. In diffusive CR propagation models the most natural…
We are constructing a model which aims to reproduce observational data of many kinds related to cosmic-ray origin and propagation: direct measurements of nuclei, antiprotons, electrons and positrons, gamma-rays, and synchrotron radiation.…
Population studies of unidentified EGRET sources suggest that there exist at least three different populations of galactic gamma-ray sources. One of these populations is formed by young objects distributed along the galactic plane with a…
It has been suggested that high-energy gamma-ray emission ($>100{\rm MeV}$) of nearby star-forming galaxies may be produced predominantly by cosmic rays colliding with the interstellar medium through neutral pion decay. The pion-decay…
Using the HEGRA system of imaging atmospheric Cherenkov telescopes, a region of the Galactic plane (-10 deg < b < 5 deg, 38 deg < l < 43 deg) was surveyed for TeV gamma-ray emission, both from point sources and of diffuse nature. The region…
Recently, an analysis of data from the Fermi Gamma Ray Space Telescope has revealed a flux of gamma rays concentrated around the inner ~0.5 degrees of the Milky Way, with a spectrum that is sharply peaked at 2-4 GeV. If interpreted as the…
We studied the problematic of uncertainties in the diffuse gamma radiation apparent in stacking analysis of EGRET data at low Galactic latitudes. Subsequently, we co-added maps of counts, exposure and diffuse background, and residuals, in…
We demonstrate that young star clusters have a $\gamma$-ray surface brightness comparable to that of the diffuse Galactic emission (DGE), and estimate that their sky coverage in the direction of the inner Galaxy exceeds unity. We therefore…
Recent observations by ground-based gamma-ray telescopes have led to the publication of catalogs listing sources observed in the TeV and PeV energy ranges. Photons of such high energy are strongly absorbed during propagation over…
Gamma-ray emission from large structures is useful for tracing the propagation and distribution of cosmic rays throughout our Galaxy. For example, the search for gamma-ray emission from Giant Molecular Clouds may allow us to probe the flux…
Structure formation in the intergalactic medium (IGM) produces large-scale, collisionless shock waves, where electrons can accelerate to highly relativistic energies. Such electrons can Compton scatter cosmic microwave background photons up…
We study diffuse gamma-ray emission at intermediate Galactic latitudes measured by the Fermi Large Area Telescope with the aim of searching for a signal from dark matter annihilation or decay. In the absence of a robust dark matter signal,…
The solar disk is a bright source of multi-GeV gamma rays, due to the interactions of hadronic cosmic rays with the solar atmosphere. However, the underlying production mechanism is not understood, except that its efficiency must be greatly…
Diffuse gamma-ray emission has long been established as the most prominent feature in the GeV sky. Although the imaging atmospheric Cherenkov technique has been successful in revealing a large population of discrete TeV gamma-ray sources, a…
It is well known that the diffuse gamma-rays are produced by the collisions between the galactic cosmic rays with the stellar matter (Hayakawa-Morrison Hypothesis). In this paper the author tries to estimate the contribution of star flares…
We show that recent $\gamma$-ray observations of the Small Magellanic Cloud with EGRET rule out a universal cosmic ray flux only at energies below $\approx 10$ GeV, while the observed diffuse X-ray and $\gamma$-ray background radiations…
Progress in the Imaging Atmospheric Cherenkov Technique has enabled first sensitive observations of the innermost few 100 pc of the Milky Way in Very High Energy (VHE; >100 GeV) gamma rays. Observations by the H.E.S.S. instrument deliver…
We consider the emission of high energy to very high energy $\gamma$-rays in radio-quiet active galactic nuclei (AGN) or the central regions of radio-loud AGN. We use our results to estimate the $\gamma$-ray flux from the central regions of…
Several popular cosmological models predict that most of the baryonic mass in the local universe is located in filamentary and sheet-like structures associated with galaxy overdensities. This gas is expected to be gravitationally heated to…
Recently, the MILAGRO collaboration reported on the detection of a diffuse multi-TeV emission from a region of the Galactic disk close to the inner Galaxy. The emission is in excess of what is predicted by conventional models for cosmic ray…