Radiation astronomy/Intensities

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Positrons from a terrestrial gamma ray flash are detected by the Fermi gamma ray telescope. Credit: NASA Goddard Space Flight Center.

Intensity astronomy focuses on creating a sufficient intensity for a desired property or characteristic that a signal may be converted in a detector to an electric current.

Theoretical radiation astronomy[edit | edit source]

Def. a time-averaged flux is called an intensity.

Backgrounds[edit | edit source]

This graph shows the power density spectrum of the extragalactic or cosmic gamma-ray background (CGB). Credit: pkisscs@konkoly.hu.

The diffuse cosmic X-ray background is indicated in the figure at right with the notation CXB.

In addition to discrete sources which stand out against the sky, there is good evidence for a diffuse X-ray background.[1] During more than a decade of observations of X-ray emission from the Sun, evidence of the existence of an isotropic X-ray background flux was obtained in 1956.[2] This background flux is rather consistently observed over a wide range of energies.[1] The early high-energy end of the spectrum for this diffuse X-ray background was obtained by instruments on board Ranger 3 and Ranger 5.[1] The X-ray flux corresponds to a total energy density of about 5 x 10−4 eV/cm3.[1] The ROSAT soft X-ray diffuse background (SXRB) image shows the general increase in intensity from the Galactic plane to the poles. At the lowest energies, 0.1 - 0.3 keV, nearly all of the observed soft X-ray background (SXRB) is thermal emission from ~106 K plasma.

Cosmic rays[edit | edit source]

The distribution of ²⁶Al in the Milky Way is shown. Credit: the COMPTEL Collaboration.
This is the CGRO gamma-ray signal from the Galactic Center region. Credit: COMPTEL Collaboration.
The flux of cosmic-ray particles is a function of their energy. Credit: Sven Lafebre, after Swordy.[3]

Some cosmic-ray observatories also look for high energy gamma rays and x-rays.

Aluminium-26, 26Al, is a radioactive isotope of the chemical element aluminium, decaying by either of the modes beta-plus or electron capture, both resulting in the stable nuclide magnesium-26. The half-life of 26Al is 7.17×105 years. This is far too short for the isotope to survive to the present, but a small amount of the nuclide is produced by collisions of argon atoms with cosmic ray protons.

Aluminium-26 also emits gamma rays and X-rays,[4] and is one of the few radionuclides to emit X-rays.

At lower right is an image indicating the range of cosmic-ray energies. The flux for the lowest energies (yellow zone) is mainly attributed to solar cosmic rays, intermediate energies (blue) to galactic cosmic rays, and highest energies (purple) to extragalactic cosmic rays.[3]

Positrons[edit | edit source]

Observation of positrons from a terrestrial gamma ray flash is performed by the Fermi gamma ray telescope. Credit: NASA Goddard Space Flight Center.

"Positron astronomy is 30 years old but remains in its infancy."[5]

"[P]ositron astronomy results ... have been obtained using the INTEGRAL spectrometer SPI".[6] The positrons are not directly observed by the INTEGRAL space telescope, but "the 511 keV positron annihilation emission is".[6]

During solar flares “[s]everal radioactive nuclei that emit positrons are also produced; [which] slow down and annihilate in flight with the emission of two 511 keV photons or form positronium with the emission of either a three gamma continuum (each photon < 511 keV) or two 511 keV photons."[7]

Electromagnetics[edit | edit source]

This image shows absorption by wavelength. X-radiation spans 3 decades in wavelength ~(8 nm - 8 pm). The last being just off the left edge at 0.008 nm. Credit: .

X-rays are electromagnetic radiation from a portion of the wavelength spectrum of about 5 to 8 nanometers (nm)s down to approximately 5 to 8 picometers (pm)s. As the figure at the left indicates with respect to surface of the Earth measurements, they do not penetrate the atmosphere. Laboratory measurements with X-ray generating sources are used to determine atmospheric penetration.

Gamma rays[edit | edit source]

This gamma-ray spectrum contains the typical isotopes of the uranium-radium decay line. Credit: Wusel007.

Elements usually emit a gamma-ray during nuclear decay or fission. The gamma-ray spectrum at right shows typical peaks for 226Ra, 214Pb, and 214Bi. These isotopes are part of the uranium-radium decay line. As 238U is an alpha-ray emitter, it is not shown. The peak at 40 keV is not from the mineral. From the color of the rock shown the yellowish mineral is likely to be autunite.

Visuals[edit | edit source]

At the bottom of this visible emission model is a visual intensity curve. Credit: Stanlekub.

Infrareds[edit | edit source]

This is a plot of Earth atmosphere transmittance in the infrared region of the electromagnetic spectrum. Credit: US Navy.

The wavelength of infrared light ranges from 0.75 to 300 micrometers. Infrared falls in between visible radiation, which ranges from 380 to 750 nanometers, and [terahertz radiation] submillimeter waves.

Infrared and optical astronomy are often practiced using the same telescopes, as the same mirrors or lenses are usually effective over a wavelength range that includes both visible and infrared light.

Far-infrared astronomy deals with objects visible in far-infrared radiation (extending from 30 [micron] µm towards submillimeter wavelengths around 450 µm).

Huge, cold clouds of gas and dust in [the Milky Way] our own galaxy, as well as in nearby galaxies, glow in far-infrared light. This is due to thermal radiation of interstellar dust contained in molecular clouds.

Visually dark infrared sources can be radiative cosmic dust, hydrogen gas such as an H II region (e.g. the Orion Nebula), an H I region of hydrogen, a molecular cloud, or a coronal cloud.

There are about 1,892,100 infrared (IR) objects in the SIMBAD database. Some of these like IRAS 20542+3631 are only IR objects. 1RXS J205444.6+361116 is an IR and an X-ray object only. These objects are visibly dark infrared sources. As is 2MASS J21074764+3802561, which is an IR and UV object only.

Chemistry[edit | edit source]

Typical energy dispersive XRF spectrum for a number of elements is shown. Credit: LinguisticDemographer.
This is a typical spectrum of a rhodium target tube operated at 60 kV, showing continuous spectrum and K lines. Credit: LinguisticDemographer.

Each element has electronic orbitals of characteristic energy. Following removal of an inner electron by an energetic photon provided by a primary radiation source, an electron from an outer shell drops into its place. There are a limited number of ways in which this can happen ... The main transitions are given names: an L→K transition is traditionally called Kα, an M→K transition is called Kβ, an M→L transition is called Lα, and so on. Each of these transitions yields a fluorescent photon with a characteristic energy equal to the difference in energy of the initial and final orbital. The wavelength of this fluorescent radiation can be calculated from Planck's Law:

The second image at right "shows the typical form of the sharp fluorescent spectral lines obtained in the energy-dispersive method.

"[E]lemental abundances which cannot be determined from meteorites include several of the most important for interstellar X-ray absorption: H, He, C, N, O, Ne, and Ar."[8]

Spatial distributions[edit | edit source]

The electric vectors of PKS0521-36 show clear structure and alignment. Credit: Keel.

"The emission of electromagnetic radiation from a superluminal (faster-than-light in vacuo) charged particle [is such] that no physical principle forbids emission by extended, massless superluminal sources. A polarization current density (dP/dt; see Maxwell's fourth equation) can provide such a source; the individual charged particles creating the polarization do not move faster than c, the speed of light, and yet it is relatively trivial to make the envelope of the polarization current density to do so."[9]

The "emitted radiation has many unusual characteristics, including: (i) the intensity of some components decays as the inverse of the distance from the source, rather than as 1/(distance)2 (i.e. these components are non-spherically-decaying); (ii) the emission is tightly beamed, the exact direction of the beam depending on the source speed; and (iii) the emission contains very high frequencies not present in the synthesis of the source. Note that the non-spherically decaying components of the radiation do not violate energy conservation. They result from the reception, during a short time period, of radiation emitted over a considerably longer period of (retarded) source time; their strong electromagnetic fields are compensated by weak fields elsewhere [1]."[9]

The "emission occupies a very small polar angular width of order 0.8 degrees in the far field. Based on these findings, we suggest that a superluminal source could act as a highly directional transmitter of MHz or THz signals over very long distances."[9]

"The magnetic field is well-ordered in many jets, as shown by polarization measurements. Synchrotron radiation can be very highly polarized (50%) if the field is globally ordered, and some sources [approach] this level. The electric vectors show clear structure and alignment; an especially common pattern is for the field lines to be along the jet in the inner portions and transition to an azimuthal configuration farther out. This is seen in [PKS0521-36 at 2 cm]."[10]

Hypotheses[edit | edit source]

  1. Intensity is a matter of separating noise from a signal.

See also[edit | edit source]

References[edit | edit source]

  1. 1.0 1.1 1.2 1.3 P Morrison. "Extrasolar X-ray Sources". Annual Review of Astronomy and Astrophysics 1967 5 (1): 325–50. doi:10.1146/annurev.aa.05.090167.001545. 
  2. Kupperian JE Jr, Friedman H (1958). "Experiment research US progr. for IGY to 1.7.58". IGY Rocket Report Ser. (1): 201. 
  3. 3.0 3.1 S. Swordy (2001). "The energy spectra and anisotropies of cosmic rays". Space Science Reviews 99: 85–94. 
  4. Nuclide Safety Data Sheet Aluminum-26. www.nchps.org. http://hpschapters.org/northcarolina/NSDS/26AlPDF.pdf. 
  5. P.A.Milne, J.D.Kurfess, R.L.Kinzer, M.D.Leising, D.D.Dixon (April 2000). Investigations of positron annihilation radiation, In: Proceedings of the 5th COMPTON Symposium. 510. Washington, DC: American Institute of Physics. pp. 21-30. doi:10.1063/1.1303167. http://arxiv.org/abs/astro-ph/9911184. Retrieved 2011-11-25. 
  6. 6.0 6.1 G. Weidenspointner, G.K. Skinner, P. Jean, J. Knödlseder, P. von Ballmoos, R. Diehl, A. Strong, B. Cordier, S. Schanne, C. Winkler (October 2008). "Positron astronomy with SPI/INTEGRAL". New Astronomy Reviews 52 (7-10): 454-6. doi:10.1016/j.newar.2008.06.019. http://www.sciencedirect.com/science/article/pii/S1387647308001164. Retrieved 2011-11-25. 
  7. Gerald H. Share and Ronald J. Murphy (January 2004). Andrea K. Dupree, A. O. Benz. ed. Solar Gamma-Ray Line Spectroscopy – Physics of a Flaring Star, In: Stars as Suns: Activity, Evolution and Planets. San Francisco, CA: Astronomical Society of the Pacific. pp. 133-44. ISBN 158381163X. Bibcode: 2004IAUS..219..133S. http://heseweb.nrl.navy.mil/gamma/solar/papers/share_iau_04.pdf. Retrieved 2012-03-15. 
  8. Robert Morrison and Dan McCammon (July 1983). "Interstellar photoelectric absorption cross sections, 0.03-10 keV". The Astrophysical Journal 270 (7): 119-22. 
  9. 9.0 9.1 9.2 J. Singleton, A. Ardavan, H. Ardavan, J. Fopma and D. Halliday (2005). Non-spherically-decaying radiation from an oscillating superluminal polarization current: possible low-power, deep-space communication applications in the MHz and THz bands, 16th International Symposium on Space Terahertz Technology. pp. 117. http://www.nrao.edu/meetings/isstt/papers/2005/2005117000.pdf. Retrieved 2014-03-18. 
  10. Bill Keel (October 2003). Jets, Superluminal Motion, and Gamma-Ray Bursts. Tucson, Arizona USA: University of Arizona. http://www.astr.ua.edu/keel/galaxies/jets.html. Retrieved 2014-03-19. 

External links[edit | edit source]