Gamma pulsar

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A gamma pulsar (en. Gamma-ray pulsar) is a magnetic neutron star which , due to its rotation, emits periodically modulated gamma radiation. In contrast to the gamma-ray binary stars , the gamma-rays are generated exclusively by changing the rotational energy of the star and not by accretion or interaction in a close binary star .

Properties and classification

The gamma pulsars are divided into radio loud and radio quiet pulsars according to their detectability in the range of radio radiation . Both groups are found predominantly along the galactic plane, have a low characteristic age of no more than 50,000 years, a magnetic flux density of more than 10 12 Gauss , their periods of rotation are in the range of 0.03 to 0.5 seconds and no longer emit than a few percent of the energy released by the slowing down of rotation in the range of gamma radiation. Examples of radio-loud gamma pulsars are the Vela pulsar and the pulsar in the Crab Nebula , while the prototype of the radio-quiet gamma pulsars is Geminga . Since the properties of radio loud and quiet gamma pulsars do not differ, a different angular expansion of the radio and gamma radiation is assumed to be the cause, which in turn is a function of the magnetic field strength and thus of age.

The gamma pulsars mainly show double pulses per rotation, the two maxima being 0.4 to 0.6 rotation periods apart. The maxima in the range of gamma radiation are generally time-shifted compared to the extrema in other wavelengths.

There are also millisecond pulsars that emit up to 15 percent of their total electromagnetic emissions in the range of gamma radiation. They have magnetic flux densities of less than 10 9 Gauss and rotation periods of 0.002 to 0.01 seconds. It is quite close objects with distances of some 100 parsecs , while the classical gamma-ray pulsars are usually more 1,000 parsecs away. Accordingly, the luminosity in the range of gamma radiation in the millisecond pulsars does not reach 10 35 erg / s , while the normal gamma pulsars achieve luminosity of up to 10 37 erg / s. The gamma millisecond pulsars are often part of a black widow , in which the radiation emitted by the pulsar removes the companion star.

Models of the origin of gamma radiation

Various models have been developed to explain the origin of high-energy radiation:

  • In the polar cap model, electron / positron pairs are formed in electrical currents above the magnetic poles, which generate synchrotron radiation. This model is used very successfully in the field of radio radiation, while it is difficult to explain the time delay of the maxima at different wavelengths
  • In the slot gap model, electron / positron pairs are generated further out in the magnetic field at a distance of a few neutron star radii.
  • In the outer gap model, electrons are accelerated far outside in the magnetosphere in the area of ​​the light cylinder up to the speed of light and emit high-energy synchrotron radiation.

None of the models listed above and their further developments can adequately explain all the properties of the gamma pulsars.

literature

  • Patrizia A. Caraveo: Gamma-ray Pulsar Revolution . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1312.2913v1 .
  • HJ Pletsch et al .: Einstein @ Home discovery of four young gamma-ray pulsars in Fermi LAT data . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1311.6427v1 .
  • Dirk Pandel, Robert Scott: Multi-wavelength studies of the gamma-ray pulsar PSR J1907 + 0602 . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1305.1959v1 .
  • Elan Stopnitzky, Stefano Profumo: Gravitational Waves from Gamma-Ray Pulsar Glitches . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1305.2466v1 .