Session W7: Cosmic Ray Spectrum and Distribution

Measuring the Ultra-High Energy Cosmic Ray Energy Spectrum with the Telescope Array

The Telescope Array experiment (TA) is the largest cosmic ray observatory in the northern hemisphere. TA consists of an array of 507 scintillation counter surface detectors (SD) augmented by three optical fluorescence telescope observatories (FD). In analyzing the data collected by the TA SD, a novel technique is employed which consists of generating a very detailed simulation that can be directly compared against actual observations. This method enables a very careful analysis with a thoroughgoing understanding of the resolution constraints in the data. The method above will be described and the most recent SD, FD, and hybrid measurements of the cosmic ray energy spectrum will be presented.   

Reconstructing the Energy of Cosmic Rays with IceTop

The IceTop cosmic ray air shower array on the surface above the IceCube neutrino observatory detects the extensive air showers that result from cosmic ray primaries with energies between 0.1 PeV and 100 PeV. This energy range is of interest because of a characteristic drop in the flux of cosmic rays at 3 PeV (the ``knee'' of the cosmic ray spectrum). The reason for this feature in the cosmic ray energy spectrum is not yet known, but it may be a result of limits on the ability of supernova remnants to accelerate protons above 3 PeV. A precision measurement of the energy spectrum in this range with IceTop could lead to a better understanding of the origin of galactic cosmic rays. We outline a method for reconstructing the energy of primary particles from the lateral distribution of charge detected by IceTop using a maximum likelihood technique. The method involves a comparison of signals in the detector to simulated events of differing energy and composition. We present results on the performance of the method and its application to data taken with IceTop in 2009.   

All-particle Cosmic Ray Energy Spectrum with IceTop

We report on a measurement of all-particle energy spectrum of cosmic rays with the IceTop air shower array. IceTop is the surface component of the IceCube Neutrino Observatory at the geographical South Pole. The data were taken during the eleven months, from June, 2010 to April 2011. During that period, IceTop consisted of 73 operational surface stations and formed a nearly symmetrical hexagon. This analysis is based only on the surface detector IceTop, and does not yet incorporate the capability to measure air showers in coincidence with the measurement of the high energy muon bundle in the deep IceCube detector. We present preliminary results for air showers in the energy range 300 TeV to 1 EeV   

Observation of cosmic ray anisotropy with the IceCube and IceTop detectors

Over the last four years, the IceCube neutrino observatory has collected a data sample of tens of billions of muon events produced by the interaction of TeV cosmic rays with the Earth's atmosphere. A data set of this size has opened the possibility of searching for anisotropy in the arrival direction of cosmic rays at different angular scales and over a wide range of energies. We report on the observation of cosmic ray anisotropy in the southern sky at median energies from 20 TeV to 400 TeV. At low energies, the anisotropy is dominated by a large angular scale feature of per-mille strength accompanied by structures with smaller amplitudes and with typical angular sizes between $10^{\circ}$ and $20^{\circ}$. At the highest energies, the cosmic ray flux still shows significant anisotropy, but with a different structure. The most significant feature is a deficit region with an angular size of about $30^{\circ}$. A preliminary analysis of data taken with the IceTop air shower array at a median energy of about 650 TeV shows an anisotropy that is consistent with the one observed by IceCube at 400 TeV.   

Anisotropy studies with the Pierre Auger Observatory

We report recent results from the Pierre Auger Observatory about the anisotropy of ultra-high energy cosmic ray arrival directions. We present the results on the search for a dipolar anisotropy at the EeV energy scale. Both the phase and the amplitude measurements of the first harmonic modulation in the right-ascension distribution are discussed. For cosmic rays with energies above 55 EeV, we present an update on the search for correlations between their arrival directions and the positions of active galactic nuclei from the V\'eron-Cetty and V\'eron catalog. Finally, we also discuss the results of correlation analyses applied to other populations of extragalactic objects.   

The JEM-EUSO Mission

The JEM-EUSO mission will study the origin of extreme energy cosmic rays (EECRs) above 100 EeV. It will measure the spectrum and angular distribution of EECRs over the full sky enabling the identification of extragalactic cosmic ray sources. It is designed to achieve an exposure above 1 million km2 sr year to open a new particle astronomy window. A wide-field (60 degrees) telescope with a diameter of about 2.5 m will look down from the International Space Station (ISS) onto the night sky to detect near UV photons (330-400nm, both fluorescent and Cherenkov photons) emitted from the giant air showers produced by EECRs. The arrival direction map with more than five hundred events will allow the identification of the nearest EECR sources with known astronomical objects and the understanding of the physics of the acceleration and propagation mechanisms. The observed energy spectra and sky map can finally confirm the GZK process and/or determine the maximum energy of astrophysical accelerators. Neutral components (neutrinos and gamma rays) may also be detected, if their fluxes are high enough. The JEM-EUSO mission is planned to be launched by a H2B rocket, transferred to the ISS by H2 Transfer Vehicle (HTV), and attached to the Exposed Facility external experiment KIBO platform.   

The Microwave Air Yield Beam Experiment (MAYBE): measurement of GHz radiation for Ultra-High Energy Cosmic Rays detection

We present measurements of microwave emission from an electron beam induced air plasma, performed at the electron Van de Graaff facility of the Argonne National Laboratory. Radio emission is studied over a wide range of frequencies between 1 and 15 GHz. This measurement provides further insight on microwave emission from extensive air showers as a novel detection technique for Ultra-High Energy Cosmic Rays.   

Microwave detection of cosmic ray showers at the Pierre Auger Observatory

Microwave emission from the electromagnetic cascade induced in the atmosphere by ultra-high energy cosmic rays (UHECR) may allow for a novel detection technique, which combines the advantages of the well-established fluorescence technique - the reconstruction of the shower profile - with a 100\% duty cycle, minimal atmospheric attenuation and the use of low-cost commercial equipment. Two complementary techniques are currently being pursued at the Pierre Auger Observatory. AMBER (Air-shower Microwave Bremsstrahlung Experimental Radiometer), MIDAS (Microwave Detection of Air Showers) and FDWave are prototypes for a large imaging dish antenna. In EASIER (Extensive Air Shower Identification using Electron Radiometer), the microwave emission is detected by antenna horns located on each surface detector of the Auger Observatory. MIDAS is a self-triggering system while AMBER, FDWave, and EASIER use the trigger from the Auger detectors to record the emission. The coincident detection of UHECR by the microwave prototype detectors and the fluorescence and surface detectors will prove the viability of this novel technique. The status of microwave R\&D activities at the Pierre Auger Observatory will be reported.   

Radar Detection of Cosmic Rays

Progress in the study of high energy cosmic ray physics is limited by low flux. In order to collect substantial statistics above $10^{19}$~eV, the two largest ground arrays currently in operation cover 800~$\mbox{km}^2$ (Telescope Array, Utah) and 3000~$\mbox{km}^2$ (Auger Observatory, Argentina). The logistics and cost of an order-of-magnitude increase in ground array aperture is prohibitive. In the literature, radar detection experiments have been proposed but substantial results have not been reported. We have deployed a low-power (1500~W) bistatic radar facility overlapping the Telescope Array (TA) in Delta, Utah. Data acquisition systems for the radar receivers were developed in parallel. This system has taught us a great deal, but our current focus is building and deploying a 40~kW transmitter and new high-gain transmitting antenna. Theoretical simulations of CR air shower scattering of radar show that coincidences with the ground array should be detected with this new system. An FCC license for the new transmitter/antenna has been obtained. Systems monitoring and data logging systems, as well as a new, intelligent self-triggered DAQ continue to be developed. We hope to deploy the self-triggered DAQ during the first few months of 2012 and complete the transmitte   

Radar Detection of High Energy Cosmic Ray Showers

The radar detection technique for High Energy Cosmic Ray Shower detection has been investigated in this collaborative work. High Energy Cosmic Ray Showers produce disk-like ionization front which moves with relativistic speed in our atmosphere. We study the reflection of radio waves such as the ones from commercial radio and TV stations from the relativistic moving front. The reflected wave experiences a high blue-shift in frequency due to relativistic Doppler Effect. The feasibility study of detection of showers via this method and the benefits will be presented.