Observation of Ultrahigh-Energy Cosmic Rays with the ANITA Balloon-Borne Radio Interferometer

Physical Review Letters (Impact Factor: 7.51). 04/2010; 105(15). DOI: 10.1103/PhysRevLett.105.151101
Source: arXiv


We report the observation of sixteen cosmic ray events of mean energy of 1.5
x 10^{19} eV, via radio pulses originating from the interaction of the cosmic
ray air shower with the Antarctic geomagnetic field, a process known as
geosynchrotron emission. We present the first ultra-wideband, far-field
measurements of the radio spectral density of geosynchrotron emission in the
range from 300-1000 MHz. The emission is 100% linearly polarized in the plane
perpendicular to the projected geomagnetic field. Fourteen of our observed
events are seen to have a phase-inversion due to reflection of the radio beam
off the ice surface, and two additional events are seen directly from above the

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    • "An alternative instrument for air shower detection is given by digital radio antenna arrays, which also can provide a measurement of the shower energy [4] [5] and feature a duty-cycle of almost 100 % like particle detector arrays [6] [7]. Current efforts like LOPES [8] [9] [10], CODALEMA [11] [12], at ANITA [13], the Pierre Auger Observatory [14], or at Tunka [15] still focus on engineering work, i.e. to prove the applicability of the radio technique to large scale observatories , and to show that a precision similar to the one of the fluorescence and air-Cherenkov techniques can be achieved. "
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    ABSTRACT: Cosmic ray air showers emit radio pulses at MHz frequencies, which can be measured with radio antenna arrays - like LOPES at the Karlsruhe Institute of Technology in Germany. To improve the understanding of the radio emission, we test theoretical descriptions with measured data. The observables used for these tests are the absolute amplitude of the radio signal, and the shape of the radio lateral distribution. We compare lateral distributions of more than 500 LOPES events with two recent and public Monte Carlo simulation codes, REAS 3.11 and CoREAS (v 1.0). The absolute radio amplitudes predicted by REAS 3.11 are in good agreement with the LOPES measurements. The amplitudes predicted by CoREAS are lower by a factor of two, and marginally compatible with the LOPES measurements within the systematic scale uncertainties. In contrast to any previous versions of REAS, REAS 3.11 and CoREAS now reproduce the shape of the measured lateral distributions correctly. This reflects a remarkable progress compared to the situation a few years ago, and it seems that the main processes for the radio emission of air showers are now understood: The emission is mainly due to the geomagnetic deflection of the electrons and positrons in the shower. Less important but not negligible is the Askaryan effect (net charge variation). Moreover, we confirm that the refractive index of the air plays an important role, since it changes the coherence conditions for the emission: Only the new simulations including the refractive index can reproduce rising lateral distributions which we observe in a few LOPES events. Finally, we show that the lateral distribution is sensitive to the energy and the mass of the primary cosmic ray particles.
    Full-text · Article · Sep 2013 · Astroparticle Physics
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    • "emplaced to assess the environment for detection of geosynchrotron RF emission from cosmic ray extensive air showers (EAS) which arrive from interactions in the atmosphere above the array. Such RF impulses have predominantly lower frequency content than shower-initiated impulses arising from within the ice [15], but have RF spectra which can extend to hundreds of MHz [16] and thus will be detected in the deeper antennas as well. The SFDs in this case can function as a way to conclusively tag EAS radio events and distinguish them from other RF interference, if the backgrounds are low enough in the VHF band. "
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    ABSTRACT: We report on studies of the viability and sensitivity of the Askaryan Radio Array (ARA), a new initiative to develop a Teraton-scale ultra-high energy neutrino detector in deep, radio-transparent ice near Amundsen-Scott station at the South Pole. An initial prototype ARA detector system was installed in January 2011, and has been operating continuously since then. We describe measurements of the background radio noise levels, the radio clarity of the ice, and the estimated sensitivity of the planned ARA array given these results, based on the first five months of operation. Anthropogenic radio interference in the vicinity of the South Pole currently leads to a few-percent loss of data, but no overall effect on the background noise levels, which are dominated by the thermal noise floor of the cold polar ice, and galactic noise at lower frequencies. We have also successfully detected signals originating from a 2.5 km deep impulse generator at a distance of over 3 km from our prototype detector, confirming prior estimates of kilometer-scale attenuation lengths for cold polar ice. These are also the first such measurements for propagation over such large slant distances in ice. Based on these data, ARA-37, the ˜200 km2 array now in its initial construction phase, will achieve the highest sensitivity of any planned or existing neutrino detector in the 1.0E16-1.0E19 eV energy range.
    Full-text · Article · Feb 2012 · Astroparticle Physics
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    ABSTRACT: We have conducted a search for extended energy deposition trails left by ultrarelativistic magnetic monopoles interacting in Antarctic ice. The nonobservation of any satisfactory candidates in the 31 days of accumulated ANITA-II (Antarctic Impulsive Transient Antenna) flight data results in an upper limit on the diffuse flux of relativistic monopoles. We obtain a 90% C.L. limit of order 10-19 (cm2 s sr)-1 for values of Lorentz factor, γ, 1010≤γ at the anticipated energy Etot=1016 GeV. This bound is stronger than all previously published experimental limits for this kinematic range.
    Full-text · Article · Jan 2011 · Physical review D: Particles and fields
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