|Cutnell & Johnson. Physics 4th Edition. New York: Wiley, 1998: 737.||1024 Hz|
|McGraw Hill Encyclopedia of Science and Technology. New York: McGraw Hill, 1997: 185.||"Frequency, Hz–1023, Wavelength, m–3 × 10−15, Nomenclature - Cosmic Photons Typical Source - Astronomical"||
|Mitton, Simon. The Crab Nebula. New York: Scribners, 1978: 74.||"Radiation is detectable from a frequency of 10 kHz, representative of long-wavelength radio waves, right through the microwave, infrared, optical, ultraviolet, and X-ray regimes, and on through to gamma rays with a frequency of 1020 Hz."||1020 Hz|
|Is there an upper limit to the Electromagnetic Spectrum? Ask a High-Energy Astronomer. Nasa Goddard Space Flight Center||"Reliable detections of very high energy gamma-ray radiation from individual astrophysical sources, specifically from a couple of active galaxies and from the Crab Nebula, have extended up to about 1027 Hz (5 × 1012 eV). Aside from these individual sources, there is also expected to be a diffuse emission of gamma-rays which accompany the isotropic flux of cosmic rays. This diffuse gamma-ray emission is well measured below around 1024 Hz (109 eV) or so, and is expected to extend up to at least 1030 Hz (1015 eV). There have been reports of measurements of diffuse gamma-ray emission above 1029 Hz, but many other groups have only reported upper limits to emission at these energies."||1030 Hz|
Electromagnetic waves are waves of energy formed by accelerating charge. They are classified by the wavelength, frequency, and energy. The electromagnetic spectrum is an illustration of such classification. At one end of the spectrum are the longer wavelength, lower frequency, and lower energy waves. At the other end are the shorter wavelength, higher frequency, and higher energy waves. The spectrum in order from the lower frequency to the higher frequency is radio waves, microwaves, infrared, visible light, ultraviolet, x-ray, and gamma ray.
Gamma rays are radiation from nuclear decay, when a nucleus changes from an excited energy state to a lower energy state. Gamma rays are typically waves of frequencies greater than 1019 Hz. They have high energies (greater than 104 eV per photon) and extremely short wavelengths (less than 10−14 m). Gamma rays can penetrate nearly all materials and are therefore difficult to detect. Gamma rays have mostly been detected in the activities in space such as the Crab Nebula and the Vela Pulsar. The highest frequency of gamma rays that have been detected is 1030Hz measured from diffuse gamma ray emissions.
Elaine Lo -- 2000