Constraints on cosmic neutrino fluxes from the Antarctic Impulsive Transient Antenna experiment
ABSTRACT We report new limits on cosmic neutrino fluxes from the test flight of the Antarctic Impulsive Transient Antenna (ANITA) experiment, which completed an 18.4 day flight of a prototype long-duration balloon payload, called ANITA-lite, in early 2004. We search for impulsive events that could be associated with ultrahigh energy neutrino interactions in the ice and derive limits that constrain several models for ultrahigh energy neutrino fluxes and rule out the long-standing Z-burst model.
- [show abstract] [hide abstract]
ABSTRACT: In the past decade there have been several attempts to detect Ultra High Energy (UHE) neutrinos via radio Ĉerenkov bursts in terrestrial ice or the lunar regolith. So far these searches have yielded no detections, but the inferred flux upper limits have started to constrain physical models for UHE neutrino generation. We report results from the Radio EVLA Search for UHE Neutrinos (RESUN) experiment, aimed at further limiting isotropic and point-source production models. RESUN uses the Expanded Very Large Array (EVLA) configured in multiple sub-arrays of four antennas observing at 1.4 GHz and pointed along the lunar limb to detect cm-wavelength Ĉerenkov bursts. No pulses of lunar origin exceeding a threshold of 0.017 μV m−1 MHz−1 were detected during a observing campaign totaling 200 h. The RESUN null detection implies an upper limit to the differential isotropic neutrino flux EdN/dE < 1 km−2 yr−1 sr−1 at 90% confidence level for sources with energy (E) exceeding 1021.2 eV and EdN/dE < 0.1 km−2 yr−1 sr−1 for E > 1022.5 eV. The isotropic flux upper limit is the lowest published for lunar searches in the range 1020.7 eV < E < 1022.3 eV and is inconsistent with extragalactic and halo Z-burst models for neutrino generation, in agreement with the ANITA Antarctic ice observations and WMAP neutrino mass estimates. Further, we establish 90% confidence differential flux limits for selected AGN sources located along the lunar celestial path.Astroparticle Physics 12/2010; · 4.78 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: Low-frequency radio astronomy is limited by severe ionospheric distortions below 50 MHz and complete reflection of radio waves below 10–30 MHz. Shielding of man-made interference from long-range radio broadcasts, strong natural radio emission from the Earth’s aurora, and the opportunity to set up a large distributed antenna array make the lunar far side a supreme location for a low-frequency radio array. A number of new scientific drivers for such an array, such as the study of the dark ages and epoch of reionization, exoplanets, and ultra-high energy cosmic rays, have emerged and need to be studied in greater detail. Here we review the scientific potential and requirements of these new scientific drivers and discuss the constraints for various lunar surface arrays. In particular, we describe observability constraints imposed by the interstellar and interplanetary medium, calculate the achievable resolution, sensitivity, and confusion limit of a dipole array using general scaling laws, and apply them to various scientific questions.Of particular interest for a lunar array are studies of the earliest phase of the universe which are not easily accessible by other means. These are the epoch of reionization at redshifts z = 6–20, during which the very first stars and galaxies ionized most of the originally neutral intergalactic hydrogen, and the dark ages prior to that.For example, a global 21-cm wave absorption signature from primordial hydrogen in the dark ages at z = 30–50 could in principle be detected by a single dipole in an eternally dark crater on the moon, but foreground subtraction would be extremely difficult. Obtaining a high-quality power spectrum of density fluctuations in the epoch of reionization at z = 6–20, providing a wealth of cosmological data, would require about 103–105 antenna elements on the moon, which appears not unreasonable in the long term. Moreover, baryonic acoustic oscillations in the dark ages at z = 30–50 could similarly be detected, thereby providing pristine cosmological information, e.g., on the inflationary phase of the universe.With a large array also exoplanet magnetospheres could be detected through Jupiter-like coherent bursts. Smaller arrays of order 102 antennas over ∼100 km, which could already be erected robotically by a single mission with current technology and launchers, could tackle surveys of steep-spectrum large-scale radio structures from galaxy clusters and radio galaxies. Also, at very low frequencies the structure of the interstellar medium can be studied tomographically. Moreover, radio emission from neutrino interactions within the moon can potentially be used to create a neutrino detector with a volume of several cubic kilometers. An ultra-high energy cosmic ray detector with thousands of square kilometer area for cosmic ray energies could in principle be realized with some hundred antennas.In any case, pathfinder arrays are needed to test the feasibility of these experiments in the not too distant future. Lunar low-frequency arrays are thus a timely option to consider, offering the potential for significant new insights into a wide range of today’s crucial scientific topics. This would open up one of the last unexplored frequency domains in the electromagnetic spectrum.New Astronomy Reviews 01/2009; · 1.82 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: The future of cm and m-wave astronomy lies with the Square Kilometre Array (SKA), a telescope under development by a consortium of 17 countries. The SKA will be 50 times more sensitive than any existing radio facility. A majority of the key science for the SKA will be addressed through large-area imaging of the Universe at frequencies from 300MHz to a few GHz. The Australian SKA Pathfinder (ASKAP) is aimed squarely in this frequency range, and achieves instantaneous wide-area imaging through the development and deployment of phase-array feed systems on parabolic reflectors. This large field-of-view makes ASKAP an unprecedented synoptic telescope poised to achieve substantial advances in SKA key science. The central core of ASKAP will be located at the Murchison Radio Observatory in inland Western Australia, one of the most radio-quiet locations on the Earth and one of the sites selected by the international community as a potential location for the SKA. Following an introductory description of ASKAP, this document contains 7 chapters describing specific science programmes for ASKAP. In summary, the goals of these programmes are as follows: – The detection of a million galaxies in atomic hydrogen emission across 75% of the sky out to a redshift of 0.2 to understand galaxy formation and gas evolution in the nearby Universe. – The detection of synchrotron radiation from 60 million galaxies to determine the evolution, formation and population of galaxies across cosmic time and enabling key cosmological tests. – The detection of polarized radiation from over 500,000 galaxies, allowing a grid of rotation measures at 10′ to explore the evolution of magnetic fields in galaxies over cosmic time. – The understanding of the evolution of the interstellar medium of our own Galaxy and the processes that drive its chemical and physical evolution. – The high-resolution imaging of intense, energetic phenomena by enlarging the Australian and global Very Long Baseline networks. – The discovery and timing of a thousand new radio pulsars. – The characterization of the radio transient sky through detection and monitoring of transient sources such as gamma ray bursts, radio supernovae and intra-day variables. The combination of location, technological innovation and scientific program will ensure that ASKAP will be a world-leading radio astronomy facility, closely aligned with the scientific and technical direction of the SKA. A brief summary chapter emphasizes the point, and considers discovery space.Experimental Astronomy 12/2008; 22:151-273. · 2.97 Impact Factor