Gamma Ray Astronomy from Space

If X-rays sample enegetic astronomical processes, gamma rays sample even more energetic processes. One of their main “uses” is to help us to find the sources of cosmic rays, which as we will see in Chap. 9 are sub-atomic particles with extreme energies. This is because gamma-rays are produced in sources which also produce cosmic rays, but they are not deviated by interactions or magnetic fields en route to us, so the source of a cosmic ray shower occurring at the same time as a gamma ray burst can be located in space. However the atmosphere shields us from gamma-rays; those with lower energies are detected from satellites, and those with higher energies are detected from the ground using the showers of particles they produce in the atmosphere (see Chap. 9). In this chapter I describe how a gamma-ray satellite telescope works, and name some of the more productive of these satellites, launched by NASA, ESA, and the Soviet space agency. You will see maps of the gamma-ray sky, of individual supernova remnants, of the “Fermi Bubbles” (huge lobes of gamma radiation emanating from the centre of our Galaxy) and of the distribution on the sky of the rapid powerful “Gamma-ray Bursts” which have been identified, with the help of gravitational wave detectors, as emanating from the mergers of neutron stars or black holes.