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. As of 2014, they are theoretical only and have not been detected. The highest energy astronomical sourced gamma rays detected are very-high-energy gamma rays.

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.[1]

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.[2]

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 till they meet the atmosphere. These photons that come through the magnetic window can make a Landau–Pomeranchuk–Migdal shower.[2]

energyenergyenergyfrequencywavelengthcomparisonproperties
eVeVJoulesHertzmeters
110.1602 aJ241.8 THz1.2398 μmnear infrared photonfor comparison
100 GeV1 × 10110.01602 μJ2.42 × 1025 Hz1.2 × 10−17 mZ boson
1 TeV1 × 10120.1602 μJ2.42 × 1026 Hz1.2 × 10−18 mflying mosquitoproduces Cherenkov light
10 TeV1 × 10131.602 μJ2.42 × 1027 Hz1.2 × 10−19 mair shower reaches ground
100 TeV1 × 10140.01602 mJ2.42 × 1028 Hz1.2 × 10−20 mping pong ball falling off a batcauses nitrogen to fluoresce
1 PeV1 × 10150.1602 mJ2.42 × 1029 Hz1.2 × 10−21 m
10 PeV1 × 10161.602 mJ2.42 × 1030 Hz1.2 × 10−22 mpotential energy of golf ball on a tee
100 PeV1 × 10170.01602 J2.42 × 1031 Hz1.2 × 10−23 mpenetrate geomagnetic field
1 EeV1 × 10180.1602 J2.42 × 1032 Hz1.2 × 10−24 m
10 EeV1 × 10191.602 J2.42 × 1033 Hz1.2 × 10−25 mair rifle shot

References

  1. ↑ Aharonian, Felix (24 August 2010). "The Fascinating TeV Sky" (PDF). WSPC - Proceedings. Retrieved 27 November 2011.
  2. 1 2 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.
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.