Peter W. Gorham

Experimental limit on the cosmic diffuse ultrahigh energy neutrino flux.

We report results from 120 h of live time with the Goldstone lunar ultrahigh energy neutrino experiment (GLUE). The experiment searches for < or = 10 ns microwave pulses from the lunar regolith, appearing in coincidence at two large radio telescopes separated by 22 km and linked by optical fiber. Such pulses would arise from subsurface electromagnetic cascades induced by interactions of > or = 100 EeV (1 EeV = 10(18) eV neutrinos in the lunar regolith. No candidates are yet seen, and the implied limits constrain several current models for ultrahigh energy neutrino fluxes.

Observation of the Askaryan Effect: Coherent Microwave Cherenkov Emission from Charge Asymmetry in High-Energy Particle Cascades

We present the first direct experimental evidence for the charge excess in high-energy particle showers and corresponding radio emission predicted nearly 40 years ago by Askaryan. We directed picosecond pulses of GeV bremsstrahlung photons at the SLAC Final Focus Test Beam into a 3.5 ton silica sand target, producing electromagnetic showers several meters long. A series of antennas spanning 0.3 to 6 GHz detected strong, subnanosecond radio-frequency pulses produced by the showers. Measurements of the polarization, coherence, timing, field strength vs shower depth, and field strength vs frequency are completely consistent with predictions. These measurements thus provide strong support for experiments designed to detect high-energy cosmic rays such as neutrinos via coherent radio emission from their cascades.

Diffraction-Limited Imaging II. Optical Aperture-Synthesis Imaging of Two Binary Stars

We have used the technique of nonredundant masking at the Hale 5 m telescope and radio VLBI imaging software are used to make optical aperture-synthesis maps of two binary stars, β Corona Borealis and σ Herculis. The dynamic range of the map of β CrB is about 50:1. For σ Her, we find a separation of 70 milliarcsec. These maps demonstrate the potential of the nonredundant masking technique for diffraction-limited imaging of astronomical objects with high dynamic range. We find that the optimal integration time for measuring the closure phase is found to be longer than that for measuring the fringe amplitude. There is not a close relationship between amplitude errors and phase errors, as is found in radio astronomy, and amplitude self-calibration is less effective at optical wavelengths than at radio wavelengths. The primary beam sensitivity correlation made in radio astronomy is not necessary in optical interferometry.

On the possibility of radar echo detection of ultra-high energy cosmic ray- and neutrino-induced extensive air showers

Abstract We revisit and extend the analysis supporting a 60-year-old suggestion that cosmic rays air showers resulting from primary particles with energies above 1018 eV should be straightforward to detect with radar ranging techniques, where the radar echoes are produced by scattering from the column of ionized air produced by the shower. The idea has remained curiously untested since it was proposed, but if our analysis is correct, such techniques could provide a significant alternative approach to air shower detection in a standalone array with high duty cycle, and might provide highly complementary measurements of air showers detected in existing and planned ground arrays such as the Flys Eye or the Auger Project. The method should be particularly sensitive to showers that are transverse to and relatively distant from the detector, and is thus effective in characterizing penetrating horizontal showers such as those that might be induced by ultra-high energy neutrino primaries.

Site Characterization and Detector Development for the Greenland Neutrino Observatory

Stephanie A. Wissel∗,a J. Avva,b K. Bechtol,b C. Deaconu,b, P. Gorham,c C. Miki,c R. Nichol,d A. Romero-Wolf,e C. Schlupf,a D. Saltzberg,a A. Vieregg,b, and G. Varner,c a Dept. of Physics and Astron., Univ. of California, Los Angeles, Los Angeles, CA 90095, USA. b KICP, Univ. of Chicago, Chicago, IL 60637, USA. c Dept. of Physics and Astron., Univ. of Hawaii, Manoa, HI 96822, USA d Dept. of Physics and Astron., University College London, London, United Kingdom. e Jet Propulsion Laboratory, Pasadena, CA 91109, USA. Email: swissel@physics.ucla.edu

New limits on a diffuse flux of ⩾100 EeV cosmic neutrinos

We report on results from about 30 hours of livetime with the Goldstone Lunar Ultra-high energy neutrino Experiment (GLUE). The experiment searches for ∼10 ns microwave pulses from the lunar regolith, appearing in coincidence at two large radio telescopes separated by about 20 km and linked by optical fiber. The pulses can arise from subsurface electromagnetic cascades induced by interactions of up-coming ∼100 EeV neutrinos in the lunar regolith. A new triggering method implemented after the first 12 hours of livetime has significantly reduced the terrestrial interference background, and we now operate at the thermal noise level. No strong candidates are yet seen. We report on limits implied by this non-detection, based on new Monte Carlo estimates of the efficiency. We also report on preliminary analysis of smaller pulses, where some indications of non-statistical excess may be present.

Hypercube data analysis in astronomy: optical interferometry and millisecond pulsar searches

Astronomical data sets are beginning to live up to their name, in both their sizes and the complexity of the analysis required. Here we discuss two astronomical data analysis problems which we have begun to implement on a hypercube concurrent processor environment: The intensive image processing required in an optical interferometry project, and the large scale power spectral analysis required by a search for millisecond-period radio pulsars. In both cases the analysis proceeds largely in the Fourier domain, and we find that the problems are readily adapted to a concurrent environment. In the following report, we outline briefly the astronomical background for each problem, then discuss the general computational requirements, and finally present possible hypercube algorithms and results achieved to date.

Recovery of diffraction-limited object autocorrelations from astronomical speckle interferograms using the CLEAN algorithm

We present a new technique for processing speckle interferometric data is presented, which uses the CLEAN algorithm, originally developed for the removal of the effects of incomplete spatial frequency coverage in aperture synthesis radio maps. Since Labeyrie first noted in 1970 that the autocorrelation of a speckle-gram preserves information up to the diffraction limit of an optical telescope, a number of different techniques have been applied to recover this information, usually by Fourier deconvolution of the average power spectrum of the specklegrams with a similar spectrum for a known point source. An alternative is to deconvolve the average autocorrelation of the specklegrams directly, rather than the power spectrum; this is where CLEAN, which has been shown to be a powerful tool in deconvolution problems, may be used. Also, because of the immunity of CLEAN to gaps in the spatial frequency coverage of the power spectrum, deconvolution is robust under conditions where regions of low signal-to-noise ratio i the raw speckle data effectively introduce such gaps. We find that CLEAN is straightforward to apply, and yields results that exceed the quality of recoveries made using at least one other existing technique. Diffraction-limited and near-diffraction-limited results are presented, using photon-noise-limited specklegrams taken with the Hale 5-m telescope at Palomar under a variety of seeing conditions.

SLAC T-510: A beam-line experiment for Radio emission from particle cascades in the presence of a magnetic field

Astrophysics, National Taiwan University, Taipei, Taiwan. 7 Dept. of Physics, Univ. of Delaware, Newark, DE 19716, USA. 8 Dept. of Physics, Stanford University, Stanford, CA, 94305, USA. 9 Dept. of Physics and Astronomy, Univ. of Hawaii, Manoa, HI 96822, USA. 10SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA. 11Karlsruher Institut fur Technologie, Institut fur Kernphysik , 76021 Karlsruhe, Germany. 12Physics Dept., College of William & Mary, Williamsburg VA 23187, USA. 13Dept. of Physics and Astronomy, University College London, London, United Kingdom. 14Karlsruher Institut fur Technologie, Institut fur Experimentelle Kernphysik, 76128 Karlsruhe,

Infrared nonredundant mask imaging at Palomar

A program of high resolution infrared imaging at Palomar Observatory, is presented. The use of nonredundant masks both as an imaging technique and as a method of analyzing various aspects of the imaging system are investigated. In particular, the technique is applied to a bright star and binary system using a three-hole mask. The method is useful for understanding certain systematic biases in data, as well as in producing high quality images despite sparse UV coverage. The use of multi-r(o) apertures along with a large bandwidth does not significantly hamper image reconstruction, but provides significant extra coverage in the UV plane.