The Short GAmma Ray Front Air Cherenkov Experiment (SGARFACE) is operated at the Whipple Observatory utilizing the Whipple 10 m γ-ray telescope. SGARFACE is sensitive to γ-ray bursts of more than 100 MeV with durations from 100 ns to 35 μs and provides a fluence sensitivity as low as 0.8 γ rays per m above 200 MeV (0.05 γ rays per m above 2 GeV) and allows to record the burst time structure.

We propose nuclear experiments using γ-ray pulses provided from high field plasma generated by high peak power laser. These γ-ray pulses have the excellent features of extremely short pulse, high intensity, and continuous energy distribution. These features are suitable for the study of explosive nucleosyntheses in novae and supernovae, such as the γ process and ν process. We discuss how to gen...

Discovered after the end of the Compton Gamma-Ray Observatory mission, the radio pulsar PSR J2021+3651 was long considered a likely counterpart of the high-energy γ-ray source 2CG 075+00 = 3EG J2021+3716= GeV J2020+3658, but it could not be confirmed due to the lack of a contemporaneous radio pulsar ephemeris to fold the sparse, archival γ-ray photons. Here, we report the discovery of γ-ray pul...

In this paper, we extend previous work on the absorption of high energy γ-rays in intergalactic space by calculating the absorption of 10 to 500 GeV γ-rays at high redshifts. This calculation requires the determination of the high-redshift evolution of the intergalactic starlight photon field, including its spectral energy distribution out to frequencies beyond the Lyman limit. To estimate this...

The propagation of γ-rays through metagalactic space is associated with pair creation and subsequent inverse-Compton scattering off low-energy background radiation. As a consequence, γ-rays of very high energy emitted by remote sources are reprocessed into the window from 10 MeV to 30 GeV conserving the injected energy. Any cosmologically distributed population of γ-ray sources therefore contri...

The very short time scale variability of TeV γ-ray emission from active galaxies suggests that the acceleration process of particles and the production of primary γ-rays likely occurs relatively close to the accretion disk. We calculate the γ-ray spectra produced in an Inverse Compton e pair cascade initiated by primary γ-rays which are injected close to the surface of the accretion disk. Possi...

The overall dynamical evolution and radiation mechanism of γ-ray burst jets are briefly introduced. Various interesting topics concerning beaming in γ-ray bursts are discussed, including jet structures, orphan afterglows and cylindrical jets. The possible connection between γ-ray bursts and neutron stars is also addressed.

We estimate the contribution of Galactic pulsars, both ordinary and millisecond pulsars (MSPs), to the high-energy (>100 MeV) diffuse γ−ray background. We pay particular attention to the high-latitude part of the background that could be confused with an extragalactic component in existing analyses that subtract a Galactic cosmicray model. Our pulsar population models are calibrated to the resu...

In this talk, we will show the beaming effect for Fermi/LAT blazars, then we discuss the correlations between γ-ray luminosity and other parameters, such as radio Doppler factors, superluminal motions, and core-dominance parameters. We also compare the Doppler factors determined from the γ-ray luminosity, X-ray emissions, and the short-term time scales with those from other methods. Our discuss...

In this paper, we present the results of Monte Carlo simulations of atmospheric showers induced by diffuse γ-rays as detected by the high-energy gamma-ray astronomy (HEGRA) system of five imaging atmospheric Čerenkov telescopes (IACTs). We have investigated the sensitivity of observations on extended γ-ray emission over the entire field of view of the instrument. We discuss a technique to searc...