Ultra-high-energy gamma ray


Ultra-high-energy gamma rays are gamma rays with photon energies higher than 100 TeV. They have a frequency higher than 2.42 × 1028 Hz and a wavelength shorter than 1.24 × 10−20 m. The existence of these rays were confirmed in 2019. The highest energy astronomical sourced gamma rays detected are very-high-energy gamma rays, with the center of the Crab Nebula being the source of the highest energy rays detected as of 2019.

Importance

Ultra-high-energy gamma rays are of importance because they may reveal the source of cosmic rays. Discounting the relatively weak effect of gravity, they travel in a straight line from their source to an observer. This is unlike cosmic rays which have their direction of travel scrambled by magnetic fields. Sources that produce cosmic rays will almost certainly produce gamma rays as well, as the cosmic ray particles interact with nuclei or electrons to produce photons or neutral pions which in turn decay to ultra-high-energy photons.
The ratio of primary cosmic ray hadrons to gamma rays also gives a clue as to the origin of cosmic rays. Although gamma rays could be produced near the source of cosmic rays, they could also be produced by interaction with cosmic microwave background by way of the Greisen–Zatsepin–Kuzmin limit cutoff above 50 EeV.
Ultra-high-energy gamma rays interact with magnetic fields to produce positron electron pairs. In the Earth's magnetic field, a 1021 eV photon is expected to interact about 5000 km above the earth's surface. The high-energy particles then go on to produce more lower energy photons that can suffer the same fate. This effect creates a beam of several 1017 eV gamma ray photons heading in the same direction as the original UHE photon. This beam is less than 0.1 m wide when it strikes the atmosphere. These gamma rays are too low-energy to show the Landau–Pomeranchuk–Migdal effect. Only magnetic field perpendicular to the path of the photon causes pair production, so that photons coming in parallel to the geomagnetic field lines can survive intact until they meet the atmosphere. These photons coming through the magnetic window can produce Landau–Pomeranchuk–Migdal showers.

energyenergyenergyfrequencywavelengthcomparisonproperties
TeVeVμJYottahertzAttometers
10−1211.602 × 10−13 μJ2.418 × 10−12 YHz1.2398 × 1012 amnear infrared photonfor comparison
Very-high-energy gamma rays0.1 TeV1 × 10110.01602 μJ24.2 YHz12 amZ boson
Very-high-energy gamma rays1 TeV1 × 10120.1602 μJ242 YHz1.2 amflying mosquitoproduces Cherenkov light
Very-high-energy gamma rays10 TeV1 × 10131.602 μJ2.42 × 103 YHz0.12 amair shower reaches ground
Very-high-energy gamma rays100 TeV1 × 101416.02 μJ2.42 × 104 YHz0.012 amping pong ball falling off a batcauses nitrogen to fluoresce
Ultra-high-energy gamma rays1000 TeV1 × 1015160.2 μJ2.42 × 105 YHz1.2 × 10−3 am
Ultra-high-energy gamma rays10 000 TeV1 × 10161602 μJ2.42 × 106 YHz1.2 × 10−4 ampotential energy of golf ball on a tee
Ultra-high-energy gamma rays100 000 TeV1 × 10171.602 × 104 μJ2.42 × 107 YHz1.2 × 10−5 ampenetrate geomagnetic field
Ultra-high-energy gamma rays1 000 000 TeV1 × 10181.602 × 105 μJ2.42 × 108 YHz1.2 × 10−6 am
Ultra-high-energy gamma rays10 000 000 TeV1 × 10191.602 × 106 μJ2.42 × 109 YHz1.2 × 10−7 amair rifle shot
Ultra-high-energy gamma rays1 220 910 000 000 000 TeV 1.22091 × 10281.95611 × 109 J1.855 × 1019 YHz 1.61623 × 10−17 am explosion of a car tank full of gasolinemaximum theoretical energy for a single photon, beyond which a wavelength smaller than a Planck length would be required