We calculate the prompt x–ray emission as a function of viewing angle for beamed Gamma–Ray Burst (GRB) sources. Prompt x-rays are inevitable due to the less highly blueshifted photons emitted at angles ∼> 1/γ relative to the beam symmetry axis, where γ is the expansion Lorentz factor. The observed flux depends on the combinations γ∆θ and γθv, where ∆θ is the beaming angle and θv is the viewing ...

Context. TeV gamma-ray emission from two massive binaries of the microquasar type, LS 5039 and LS I +61o 303, show clear variability with their orbital periods. Aims. Our purpose is to calculate the GeV and TeV γ-ray light curves from the massive binary LS 5039 which are expected in the specific Inverse Compton e pair cascade model. This model successfully predicted the basic features of the hi...

We describe the properties of the blazars detected by EGRET and summarize the results on the calculations of the evolution and luminosity function of these sources. Of the large number of possible origins of extragalactic diffuse γ-ray emission, it has been postulated that active galaxies might be one of the most likely candidates. However, some of our recent analysis indicate that only 25% of ...

The suggested association between the sources of γ-ray bursts (GRB’s) and the sources of ultra-high energy cosmic rays (UHECR’s) is based on two arguments: (i) The constraints that UHECR sources must satisfy to allow proton acceleration to > 1020 eV are similar to those inferred for GRB sources from γ-ray observations, and (ii) The average energy generation rate of UHECR’s is similar to the γ-r...

Two massive binaries, Cyg X-3 and LSI 303+61, are inside the error boxes of γ-ray sources detected by the Compton GRO. If somewhere inside such binary systems are injected very high energy (VHE) γ-rays, as suggested by some Cherenkov observations, they may initiate the inverse Compton e± pair cascade in the soft radiation of a massive companion, and the detected high energy γ-ray emission may b...

The RHESSI observations consist of imaging spectroscopy in the γ-ray, hard X-ray, and “firm X-ray” (3-20 keV) bands. These data are now the most extensive and capable solar high-energy observations at high spectral and spatial resolution. The low-energy hard X-ray spectrum bridges the thermal and non-thermal ranges of solar electron distributions in flares systematically for the first time. In ...

At least one massive binary system containing an energetic pulsar, PSR B125963/SS2883, has been recently detected in the TeV γ-rays by the HESS telescopes. These γ-rays are likely produced by particles accelerated in the vicinity of the pulsar and/or at the pulsar wind shock, in comptonization of soft radiation from the massive star. However, the process of γ-ray production in such systems can ...

We report on Chandra imaging observations of the Galactic Unidentified γ-ray source GEV J1809-2327, comparing the X-ray images with new VLA 1.46 GHz and 4.86 GHz maps. The X-ray images reveal a point source connected to a non-thermal X-ray/radio nebula, supporting a pulsar/wind model for the γ-ray emitter. We also detect numerous X-ray sources from the young stellar association in the adjacent ...

Complementary views of galaxy clusters in the radio synchrotron, hard X-ray inverse Compton, and high-energy γ-ray regimes are critical in calibrating them as high-precision cosmological probes. We present predictions for scaling relations between cluster mass and these non-thermal observables. To this end, we use high-resolution simulations of a sample of galaxy clusters spanning a mass range ...

The Liquid Xenon Gamma-Ray Imaging Telescope (LXeGRIT) is a balloon born experiment sensitive to γ–rays in the energy band of 0.2–20 MeV. The main detector is a time projection chamber filled with high purity liquid xenon (LXeTPC), in which the three–dimensional location and energy deposit of individual γ–ray interactions are accurately measured in one homogeneous volume. To determine the γ–ray...