We report observations with the Chandra X-ray Observatory of a field in the γ-Cygni supernova remnant (SNR78.2+2.1) centered on the cataloged location of the unidentified, bright γ-ray source 3EG J2020+4017. In this search for an X-ray counterpart to the γ-ray source, we detected 30 X-ray sources. Of these, we found 17 strong-candidate counterparts in optical (visible through near-infrared) cat...

Gamma-ray photons from young pulsars allow the deepest insight into the properties and interactions of high-energy particles with magnetic and photon fields in a pulsar magnetosphere. Measurements with the Compton Gamma-Ray Observatory have led to the detection of nearly ten γ-ray pulsars . Although quite a variety of individual signatures is found for these pulsars, some general characteristic...

We discuss the contribution of kiloparsec-scale jets in FR I radio galaxies to the diffuse γ-ray background radiation. The analyzed γ-ray emission comes from inverse-Compton scattering of starlight photon fields by the ultrarelativistic electrons whose synchrotron radiation is detected from such sources at radio, optical and X-ray energies. We find that these objects, under the minimum-power hy...

We discuss the contribution of kiloparsec-scale jets in FR I radio galaxies to the diffuse γ-ray background radiation. The analyzed γ-ray emission is due inverse-Compton scattering of starlight photon fields by the ultrarelativistic electrons whose synchrotron radiation is detected from such sources at radio, optical and X-ray energies. We find that these objects, under the minimum-power hypoth...

This article reviews the present status of high energy γ-ray astronomy at energies above 30 MeV. Observations in the past decade using both spaceand ground-based experiments have been primarily responsible for giving a tremendous boost to our knowledge of the high energy Universe. High energy γ-rays have been detected from a wide range of Galactic and extragalactic astrophysical sources, such a...

The Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescope, located on the Canary Island of La Palma at the Roque de los Muchachos observatory (ORM), is currently the largest single-dish Imaging Air Cherenkov Telescope (IACT) in operation. MAGIC is a third generation telescope comprising a number of improvements and innovative technologies to reduce the threshold energy for the detecti...

We examine the cosmic ray proton (CRp) population within the giant elliptical galaxy M 87 using the TeV γ-ray detection of the HEGRA collaboration. In our scenario, the γ-rays are produced by decaying pions which result from hadronic CRp interactions with thermal gas of the interstellar medium of M 87. By comparing the γ-ray emission to upper limits from EGRET, we constrain the spectral index o...

The case of γ-ray absorption due to photon-photon pair production of jet photons in the external photon environment like accretion disk and broad-line region radiation field of γ-ray loud active galactic nuclei (AGN) that exhibit strong emission lines is considered. I demonstrate that this ”local opacity”, if detected, will almost unavoidably be redshift-dependent in the sub-TeV range. This int...

Centaurus A, the cosmic ray accelerator a few Mpc away from us is possibly one of the nearest sources of extremely high energy cosmic rays. We investigate whether the gamma ray data currently available from Centaurus A in the GeV-TeV energy band can be explained with only proton proton interactions. We show that for a single power law proton spectrum, mechanisms of γ-ray production other than p...

Centaurus A, the cosmic ray accelerator a few Mpc away from us is possibly one of the nearest sources of extremely high energy cosmic rays. We investigate whether the gamma ray data currently available from Centaurus A in the GeV-TeV energy band can be explained with only proton proton interactions. We show that for a single power law proton spectrum, mechanisms of γ-ray production other than p...