Gamma-Ray Astronomy at the Highest Energies

Abstract

In 1983 ultra high energy γ-rays were detected from Cygnus X-3. This was of particular interest since it is the first identifiable source of cosmic rays. Since then, there has been an explosion of interest in the field with more than twenty air shower arrays planned or being used to search for γ-rays at energies above 1014 eV. Observational techniques for both very high energy and ultra high energy γ-ray astronomy are described and existing and proposed experiments reviewed with particular reference to their geographical locations. The results obtained so far are summarised together with some of the models proposed to explain them.

Centaurus A at Ultra-High Energies

“…The absorption feature progressively weakens at higher energies and, for sources within our galaxy, at much higher energies the absorption dip may be passed and photon attenuation may be reduced (Protheroe 1986a). However, for photons from the more distant Cen A with a much greater path length, the absorption will be strong up to 10 EeV (Protheroe 1986b). The Pierre Auger Observatory (PAO; see Section 11) is capable of selecting photons from its overall detected flux at such energies and a search for photons from Cen A above 10 EeV would seem worthwhile.…”

New INTEGRAL sources and TeV emission

“…The possible detection of HMXB in the TeV range in the 80's (see Protheroe 1986 for a review) led to the idea that protons trapped in the outer and closed regions of a neutron star magnetosphere could be accelerated up to γ ≈ 10 8 by multiple scattering of Alfvén waves close to the accretion column (Katz and Smith 1988). Protons could be accelerated to high energies only if the synchrotron loss time is larger than the travel time needed to bounce back often enough to gain energy.…”

Some problems of very high-energy gamma-ray astronomy

“…First of all they are pulsars such as in the Crab nebula and Vela (see for details [ 1,2]). Gamma-quanta fluxes with energies of 1011-1013 eV are being observed in the Crab since 1968.…”