Electromagnetic Air Showers Research Articles

Cosmic ray physics with the Auger Engineering Radio Array (AERA)

The Auger Engineering Radio Array consists of 153 autonomous radio stations at the site of the Pierre Auger Observatory in Malargüe, Province of Mendoza, Argentina. Covering an area of 17 km2, AERA is the largest radio detector worldwide for ultra-high energy cosmic ray (UHECR) physics. The radio stations are sensitive in the 30 to 80 MHz band and measure the coherent radio signal emitted by the electromagnetic air shower component.Steady progress in radio detection techniques and a very good understanding of the radio emission mechanism made AERA a capable tool for cosmic ray physics: We use AERA radio data to reconstruct the arrival direction and the energy of the air shower with a precision competitive with standard reconstruction techniques. Even the determination of the absolute energy scale seems possible. The primary mass composition is determined from the distribution of the shower maximum, which is currently measured with a precision of 40 g/cm2 by the radio method. Furthermore, since radio measurements are purely sensitive to the electromagnetic component of the air shower, they can be combined with measurements of particle detectors for an additional way to estimate the mass of the primary particle by means of the electron-to-muon ratio.This contribution reviews the recent analysis methods for radio signals and shows some results for the determination of air shower properties gained with AERA.

On the background of low threshold imaging Cherenkov telescopes induced by cosmic ray electrons

The next generation large diameter (⩾20m) imaging atmospheric Cherenkov telescopes should allow reduction of the threshold of detection of gamma-rays down to several GeV. At such low energies, the background events can be dominated by cosmic ray electrons. In this paper we estimate the detection energy threshold of a large diameter atmospheric Cherenkov telescope with respect to the diffuse cosmic ray electrons. It is shown that the detection energy threshold of cosmic ray electron induced showers is higher than that for primary gamma showers due to the differences in the development of electromagnetic air showers initiated by these primaries. This can provide a background-free detection region for primary gamma-rays with energy E⩽5–10GeV, provided that the misclassified events induced by primary hadrons of significantly higher energies and muons are effectively suppressed.

Cherenkov light in electron-induced air showers

In this paper, we present the results of a comparative analysis of the Cherenkov light produced by electromagnetic air showers initiated by primary gamma-rays and electrons. It is shown that the lateral distribution functions of the Cherenkov light initiated by these showers are different. This fact is explained by the difference in the development of cascades from gamma-rays and electrons; electron-showers start to develop and produce light earlier than gamma-showers, but they attenuate rapidly. By propagating much farther into the atmosphere, the gamma-initiated shower carries a Cherenkov component much closer to the ground level than electron initiated showers do; this results in a more intense pool of light close to the shower axis. The difference in the altitudes of electron- and gamma-air showers maximums logarithmically decreases with the energy and is more significant for low energy showers with E ⩽ 20 GeV. This can be important for low energy threshold Cherenkov telescopes (below 10 GeV), in which case the background events are due to diffuse cosmic ray electrons only. The minimum energy of primary electrons required for their reliable detection by an imaging atmospheric telescope will be higher than that for primary gamma-rays. For the reasonable value of the geomagnetic field strength of B ⩾ 0.3 G and at the initial energies of E ⩽ 20 GeV, the pulse width of the Cherenkov light generated by electron-showers is considerably larger than that from gamma-showers. At higher energies the shapes of Cherenkov pulse from showers induced by both primaries become almost similar.

Observation of TeV Gamma Rays from the Crab Nebula with Milagro Using a New Background Rejection Technique

The recent advances in TeV gamma-ray astronomy are largely the result of the ability to differentiate between extensive air showers generated by gamma rays and hadronic cosmic rays. Air Cherenkov telescopes have developed and perfected the "imaging" technique over the past several decades. However until now no background rejection method has been successfully used in an air shower array to detect a source of TeV gamma rays. We report on a method to differentiate hadronic air showers from electromagnetic air showers in the Milagro gamma ray observatory, based on the ability to detect the energetic particles in an extensive air shower. The technique is used to detect TeV emission from the Crab nebula. The flux from the Crab is estimated to be 2.68(+-0.42stat +- 1.4sys) x10^{-7} (E/1TeV)^{-2.59} m^{-2} s^{-1} TeV^{-1}, where the spectral index is assumed to be as given by the HEGRA collaboration.

Pattern recognition trigger electronics for an imaging atmospheric Cherenkov telescope

For imaging atmospheric Cherenkov telescopes, which aim to detect electromagnetic air showers with cameras consisting of several hundred photomultiplier pixels, the single pixel trigger rate is dominated by fluctuations in night sky brightness and by ion feedback in the photomultipliers. Pattern recognition trigger electronics may be used to reject night sky background images, thus reducing the data rate to a manageable level. The trigger system described here detects patterns of 2, 3 or 4 adjacent pixel signals within a 331 pixel camera and gives a positive trigger decision in 65 ns . The candidate pixel pattern is compared with the contents of a pre-programmed memory. With the trigger decision timing controlled by a fixed delay the time-jitter inherent in the use of programmable gate arrays is avoided. This system is now in routine operation at the Whipple 10 m Telescope.

The lateral distribution of the electrons in the electromagnetic air shower

We report the results on the lateral distribution of electrons in electromagnetic air showers generated by 10 ÷ 109 GeV photons in a wide range of distances from the shower core. We demonstrate a new scaling property and give a parametrization of the invariate part of the electron lateral distribution which enable to solve the problems of the design studies of new large air-shower arrays and interpretation of the observational data.

Semianalytical Monte Carlo method and simulations of extremely high energy electromagnetic air showers

A rapid growth of a computational time with a primary particle energy is one of the most important problems arising with the Monte Carlo simulations of extremely high energy electromagnetic cascades. A new approach — the semianalytical Monte Carlo (SAMC) method — is proposed to resolve this problem. The SAMC method provides a rather weak (logarithmic) dependence of the computational time on the cascade primary energy and can be effectively used for the simulations in a broad primary energy extent far beyond 10 16 eV. The extended simulations of the different characteristics of ultra high energy electromagnetic air showers have proved the accuracy and effectiveness of the SAMC method.