Ultra-high-energy gamma ray
Ultra-high-energy gamma rays are gamma rays with photon energies higher than 100 TeV (0.1 PeV). 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.[1] The highest energy astronomical sourced gamma rays detected are very-high-energy gamma rays, with the center of the Crab Nebula (thought to contain a rapidly spinning neutron star, or 'pulsar') 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.[2]
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.[3]
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.[3]
| Class | energy | energy | energy | frequency | wavelength | comparison | properties |
|---|---|---|---|---|---|---|---|
| TeV | eV | μJ | yottahertz | attometers | |||
| 10−12 | 1 | 1.602 × 10−13 μJ | 2.418 × 10−12 YHz | 1.2398 × 1012 am | near infrared photon | (for comparison) | |
| 0.1 TeV | 1 × 1011 | 0.01602 μJ | 24.2 YHz | 12 am | Z boson | ||
| Very-high-energy gamma rays | |||||||
| 1 TeV | 1 × 1012 | 0.1602 μJ | 242 YHz | 1.2 am | flying mosquito | produces Cherenkov light | |
| 10 TeV | 1 × 1013 | 1.602 μJ | 2.42 × 103 YHz | 0.12 am | air shower reaches ground | ||
| 100 TeV | 1 × 1014 | 16.02 μJ | 2.42 × 104 YHz | 0.012 am | ping pong ball falling off a bat | causes nitrogen to fluoresce | |
| Ultra-high-energy gamma rays | |||||||
| 1000 TeV | 1 × 1015 | 160.2 μJ | 2.42 × 105 YHz | 1.2 × 10−3 am | |||
| 10 000 TeV | 1 × 1016 | 1602 μJ | 2.42 × 106 YHz | 1.2 × 10−4 am | potential energy of golf ball on a tee | ||
| 100 000 TeV | 1 × 1017 | 1.602 × 104 μJ | 2.42 × 107 YHz | 1.2 × 10−5 am | |||
| 1 000 000 TeV | 1 × 1018 | 1.602 × 105 μJ | 2.42 × 108 YHz | 1.2 × 10−6 am | |||
| 10 000 000 TeV | 1 × 1019 | 1.602 × 106 μJ | 2.42 × 109 YHz | 1.2 × 10−7 am | air rifle shot | ||
| 1.22091×1016 TeV | 1.22091 × 1028 | 1.95611 × 109 J | 1.855 × 1019 YHz | 1.61623 × 10−17 am | explosion of a car tank full of gasoline | maximum photon energy | |
| Planck energy |
References
- ^ Yrika, Bob (June 26, 2019). "Highest energy photons ever recorded coming from Crab Nebula". phys.org. Retrieved December 20, 2019.
- ^ Aharonian, Felix (24 August 2010). "The Fascinating TeV Sky" (PDF). The Twelfth Marcel Grossmann Meeting. pp. 368–380. Bibcode:2012mgm..conf..368A. doi:10.1142/9789814374552_0016. ISBN 978-981-4374-51-4. Retrieved 27 November 2011.
{{cite book}}:|work=ignored (help) - ^ a b Vankov, H. P.; Inoue, N.; Shinozaki, K. (2 February 2008). "Ultra-High Energy Gamma Rays in Geomagnetic Field and Atmosphere" (PDF). Retrieved 3 December 2011.