No abstract

We report the observation of sixteen cosmic ray events of mean energy of 1.5 × 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 horizon.The origin of ultra-high energy cosmic rays (UHECR) remains a mystery decades after their discovery [1,2]. Key to the solution will be increased statistics on events of high enough energy (≥ 3 × 10 19 eV) to elucidate the endpoint of the UHECR energy spectrum as seen at Earth. The primary difficulty is the extreme rarity of events at these energies. Despite steady progress with experiments such as the Pierre Auger Observatory, there remains room for new methodologies. Cosmic rays have been detected for decades via impulsive radio geosynchrotron emission [3,[5][6][7][8][9][10][11][12][13][14][15][16]] but until now not in this crucial energy range, which offers the possibility of pointing the UHECRs back to their sources. We present data from the Antarctic Impulsive Transient Antenna (ANITA) [21] which represents the first entry of radio techniques into this energy range. We find 16 UHECR events, at least 40% of which are above 10 19 eV, and we show compelling evidence of their origin as geosynchrotron emission from cosmic-ray showers. Our results indicate degree-scale precision for reconstruction of the UHECR arrival direction, lending strong credence to efforts to develop radio geosynchrotron detection as a competitive method of UHECR particle astronomy.Geosynchrotron emission arises when the electron-positron particle cascade initiated by a primary cosmic ray encounters the Lorentz force in the geomagnetic field. The resulting acceleration deflects the electrons and positrons and they begin to spiral in opposite directions around the field lines [17,18]. In air, the particles' radiation length is of order 40 g cm −2 , a kilometer or less at the altitudes of air shower maximum development. Particle trajectories form partial arcs around the field lines before they lose enough energy to drop out of the shower. The meter-scale longitudinal thickness of the shower particle 'pancake' is comparable to radio wavelengths below several hundred MHz; thus the ensemble behavior of all of the cascade particles yields forward-beamed synchrotron emission which is partially or fully coherent in the radio regime. Therefore, the resulting radio impulse power grows quadratically with primary particle energy, and at the highest energies, yields radio pulses that are detectable at large distances. Current systems under development for detection of thes...

We report initial results of the first flight of the Antarctic Impulsive Transient Antenna (ANITA-1) 2006-2007 Long Duration Balloon flight, which searched for evidence of a diffuse flux of cosmic neutrinos above energies of E ν ≃ 3 × 10 18 eV. ANITA-1 flew for 35 days looking for radio impulses due to the Askaryan effect in neutrino-induced electromagnetic showers within the Antarctic ice sheets. We report here on our initial analysis, which was performed as a blind search of the data. No neutrino candidates are seen, with no detected physics background. We set model-independent limits based on this result. Upper limits derived from our analysis rule out the highest cosmogenic neutrino models. In a background horizontal-polarization channel, we also detect six events consistent with radio impulses from ultra-high energy extensive air showers.In all standard models for ultra-high energy cosmic ray (UHECR) propagation, their range is ultimately limited by the opacity of the cosmic microwave background radiation. The UHECR energy above which this becomes significant is about 6 × 10 19 eV in the current epoch. This cuts off their travel beyond distances of order 50 Mpc as first noted by Greisen [1], and Zatseptin and Kuzmin [2] (GZK). As a result of this absorption, the UHECR energy above this GZK cutoff is ultimately converted to photons, neutrinos, and lower energy hadrons. The resulting neutrinos were first described by Berezinsky and Zatsepin (BZ) [3]. In standard UHECR source models the BZ neutrino fluxes peak at energies about 2 orders of magnitude below the GZK energy. Thus a "guaranteed" flux of neutrinos at energies of E ν = 10 17−20 eV exists. Its detection is one of the clearest ways to reveal the nature and cosmic distribution of the UHECR sources [4], which is one of the longest-standing problems in high energy astrophysics.The ANITA-1 Long Duration Balloon experiment was designed specifically to search for this cosmogenic BZ neutrino flux. ANITA-1 exploits the Askaryan effect, in which strong coherent radio emission arises from electromagnetic showers in any dielectric medium [5]. The effect was first observed in 2000 [6], and has now been clearly confirmed and characterized for ice as the medium, as part of the pre-flight calibration of the ANITA-1 payload [7]. A prior flight of a prototype payload called ANITA-lite in 2003ANITA-lite in -2004 led to validation of the technique and initial neutrino flux limits that ruled out several UHE neutrino models [8].In a previous paper [9], we describe in detail the ANITA-1 instrument, payload, and flight system. Reference [9] also includes details of the instrument performance during the flight, estimates of the overall sensitivity of the instrument to neutrino fluxes, and discussions of possible backgrounds. Because of the complexity of the flight system and methodology, we refer the reader to ref.[9] for more detail when necessary.The ANITA-1 payload (Fig. 1) launched from Williams Field, Antarctica near McMurdo station, on December 15, 2006, and executed m...

A many-particle fully quantized theory for a free-electron laser which is valid in the high-gain regime is presented. We examine quantum corrections for the high-gain single-pass free-electron laser. It is shown that quantum effects become significant when the photon energy becomes comparable to the gain bandwidth. The initiation of the free-electron laser process from quantum fluctuations in the position and momentum of the electrons is considered, and the parameter regime for enhanced start-up is identified. Photon statistics of the free-electron laser radiation are discussed, and the photon number statistics for the self-amplified spontaneous emission are calculated.