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Register a new userIn situ radioglaciological measurements near Taylor Dome, Antarctica and implications for UHE neutrino astronomy
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Radiowave detection of the Cherenkov radiation produced by neutrino-ice collisions requires an understanding of the radiofrequency (RF) response of cold polar ice. We herein report on a series of radioglaciological measurements performed approximately 10 km north of Taylor Dome Station, Antarctica from Dec. 6, 2006 - Dec. 16, 2006. Using RF signals broadcast from: a) an englacial discone, submerged to a depth of 100 meters and broadcasting to a surface dual polarization horn receiver, and b) a dual-polarization horn antenna on the surface transmitting signals which reflect off the underlying bed and back up to the surface receiver, we have made time-domain estimates of both the real (index-of-refraction) and imaginary (attenuation length) components of the complex ice dielectric constant. We have also measured the uniformity of ice response along two orthogonal axes in the horizontal plane. We observe a wavespeed asymmetry of order 0.1%, projected onto the vertical propagation axis, consistent with some previous measurements, but somewhat lower than others.
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UHE neutrinos with $E>10^{17}$ eV can be produced by ultra-high energy cosmic rays (UHECR) interacting with CMB photons (cosmogenic neutrinos) and by top-down sources, such as topological defects (TD), superheavy dark matter (SHDM) and mirror matter. Cosmogenic neutrinos are reliably predicted and their fluxes can be numerically evaluated using the observed flux of UHECR. The lower limit for the flux is obtained for the case of pure proton composition of the observed UHECR. The rigorous upper limit for cosmogenic neutrino flux also exists. The maximum neutrino energy is determined by maximum energy of acceleration, which at least for the shock acceleration is expected not to exceed $10^{21} - 10^{22}$ eV. The top-down sources provide neutrino energies a few orders of magnitude higher, and this can be considered as a signature of these models. Oscillations play important role in UHE neutrino astronomy. At production of cosmogenic neutrinos $tau$-neutrinos are absent and $bar{ u}_e$ neutrinos are suppressed. These species, important for detection, appear in the observed fluxes due to oscillation. Mirror neutrinos cannot be observed directly, but due to oscillations to ordinary neutrinos they can provide the largest neutrino flux at the highest energies.
Over the past few years a major effort has been put into the exploration of potential sites for the deployment of submillimetre astronomical facilities. Amongst the most important sites are Dome C and Dome A on the Antarctic Plateau, and the Chajnantor area in Chile. In this context, we report on measurements of the sky opacity at 200 um over a period of three years at the French-Italian station, Concordia, at Dome C, Antarctica. We also present some solutions to the challenges of operating in the harsh polar environ- ment. Dome C offers exceptional conditions in terms of absolute atmospheric transmission and stability for submillimetre astron- omy. Over the austral winter the PWV exhibits long periods during which it is stable and at a very low level (0.1 to 0.3 mm). Higher values (0.2 to 0.8 mm) of PWV are observed during the short summer period. Based on observations over three years, a transmission of around 50% at 350 um is achieved for 75% of the time. The 200-um window opens with a typical transmission of 10% to 15% for 25% of the time. Dome C is one of the best accessible sites on Earth for submillimetre astronomy. Observations at 350 or 450 {mu}m are possible all year round, and the 200-um window opens long enough and with a sufficient transparency to be useful. Although the polar environment severely constrains hardware design, a permanent observatory with appropriate technical capabilities is feasible. Because of the very good astronomical conditions, high angular resolution and time series (multi-year) observations at Dome C with a medium size single dish telescope would enable unique studies to be conducted, some of which are not otherwise feasible even from space.
We present low-resolution turbulence profiles of the atmosphere above Dome C, Antarctica, measured with the MASS instrument during 25 nights in March-May 2004. Except for the lowest layer, Dome C has significantly less turbulence than Cerro Tololo and Cerro Pachon. In particular, the integrated turbulence at 16 km is always less than the median values at the two Chilean sites. From these profiles we evaluate the photometric noise produced by scintillation, and the atmospheric contribution to the error budget in narrow-angle differential astrometry. In comparison with the two mid-latitude sites in Chile, Dome C offers a potential gain of about 3.6 in both photometric precision (for long integrations) and narrow-angle astrometry precision. These gain estimates are preliminary, being computed with average wind-speed profiles, but the validity of our approach is confirmed by independent data. Although the data from Dome C cover a fairly limited time frame, they lend strong support to expectations that Dome C will offer significant advantages for photometric and astrometric studies.
Seeing, the angular size of stellar images blurred by atmospheric turbulence, is a critical parameter used to assess the quality of astronomical sites. Median values at the best mid-latitude sites are generally in the range of 0.6--0.8,arcsec. Sites on the Antarctic plateau are characterized by comparatively-weak turbulence in the free-atmosphere above a strong but thin boundary layer. The median seeing at Dome C is estimated to be 0.23--0.36 arcsec above a boundary layer that has a typical height of 30,m. At Dome A and F, the only previous seeing measurements were made during daytime. Here we report the first direct measurements of night-time seeing at Dome A, using a Differential Image Motion Monitor. Located at a height of just 8,m, it recorded seeing as low as 0.13,arcsec, and provided seeing statistics that are comparable to those for a 20,m height at Dome C. It indicates that the boundary layer was below 8,m 31% of the time. At such times the median seeing was 0.31,arcsec, consistent with free-atmosphere seeing. The seeing and boundary layer thickness are found to be strongly correlated with the near-surface temperature gradient. The correlation confirms a median thickness of approximately 14,m for the boundary layer at Dome A, as found from a sonic radar. The thinner boundary layer makes it less challenging to locate a telescope above it, thereby giving greater access to the free-atmosphere.
The recent observation by the IceCube neutrino observatory of an astrophysical flux of neutrinos represents the first light in the nascent field of neutrino astronomy. The observed diffuse neutrino flux seems to suggest a much larger level of hadronic activity in the non-thermal universe than previously thought and suggests a rich discovery potential for a larger neutrino observatory. This document presents a vision for an substantial expansion of the current IceCube detector, IceCube-Gen2, including the aim of instrumenting a $10,mathrm{km}^3$ volume of clear glacial ice at the South Pole to deliver substantial increases in the astrophysical neutrino sample for all flavors. A detector of this size would have a rich physics program with the goal to resolve the sources of these astrophysical neutrinos, discover GZK neutrinos, and be a leading observatory in future multi-messenger astronomy programs.
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