On the nature of radio-wave radiation from particle cascades

The radio emission from particle cascades was discovered sometime during the 20th century, but it wasn’t used much until recently. Due to technical advances in radio astronomy and improved theoretical knowledge of radio emission, this method has been implemented in many experiments such as LOFAR, LOPES, CODALEMA, and AERA since the early 2000s.

We have numerical codes to model the radio emission from particle cascades in air, ice and possibly other media. This article discusses a simplified version of particle cascades to explain the radio emission predicted by these codes qualitatively. It also predicts why the nature of each type of emission changes depending on the medium and observation frequency.

Askaryan Radiation:

  • Dominant component in ice
  • Bremmstrahlung and Cherenkov radiation
  • Up to a hundred MHz, predominantly Cherenkov-like in ice and bremsstrahlung-like in air.

Geomagnetic radiation

  • Dominant component in air
  • Transverse current radiation and synchrotron
  • If the shower develops within 20 km altitude, the resulting emission will resemble transverse current radiation if observed below 100 MHz.

Experimental prospects

  • Changing observation frequency for particle cascades in dense media will result in a little change in the nature of radiation.
  • Changing the observation frequency for EAS from 100 MHz to a few GHz should change the Askaryan radiation from bremsstrahlung-like to Cherenkov-like, and geomagnetic radiation from transverse-current-like to synchrotron-like. It also suggests how to search for these effects.

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