17751265
Enabling Next-Generation Dark Energy and Epoch of Reionization Radio Observatories with the MOFF Correlator
ABSTRACT.Proposed 21 cm cosmology observatories for studying the epoch of reionization (z ≈ 6–15z≈6–15) and dark energy (z ≈ 0–6z≈0–6) envision compact arrays with tens of thousands of antenna elements. Fully correlating this many elements is computationally expensive using traditional XF or FX correlators and has led some groups to reconsider direct imaging/FFT correlators. In this article we develop a variation of the direct imaging correlator that we call the MOFF correlator. The MOFF correlator shares the computational advantages of a direct imaging correlator, while avoiding a number of its shortcomings. In particular, the MOFF correlator makes no constraints on the antenna arrangement or type; provides a fully calibrated output image, including wide-field polarimetry and noncoplanar baseline effects; and can be orders of magnitude more efficient than XF or FX correlators for compact radio cosmology arrays.
119242483
The Baryon Acoustic Oscillation Broadband and Broad-beam Array: Design Overview and Sensitivity Forecasts
This work describes a new instrument optimized for a detection of the neutral hydrogen 21 cm power spectrum between redshifts of 0.5 and 1.5: the Baryon Acoustic Oscillation Broadband and Broad-beam (BAOBAB) array. BAOBAB will build on the efforts of a first generation of 21 cm experiments that are targeting a detection of the signal from the Epoch of Reionization at z ~ 10. At z ~ 1, the emission from neutral hydrogen in self-shielded overdense halos also presents an accessible signal, since the dominant, synchrotron foreground emission is considerably fainter than at redshift 10. The principle science driver for these observations are baryon acoustic oscillations in the matter power spectrum which have the potential to act as a standard ruler and constrain the nature of dark energy. BAOBAB will fully correlate dual-polarization antenna tiles over the 600-900 MHz band with a frequency resolution of 300 kHz and a system temperature of 50 K. The number of antennas will grow in staged deployments, and reconfigurations of the array will allow for both traditional imaging and high power spectrum sensitivity operations. We present calculations of the power spectrum sensitivity for various array sizes, with a 35 element array measuring the cosmic neutral hydrogen fraction as a function of redshift, and a 132 element system detecting the BAO features in the power spectrum, yielding a 1.8% error on the z ~ 1 distance scale, and, in turn, significant improvements to constraints on the dark energy equation of state over an unprecedented range of redshifts from ~0.5 to 1.5.
125296828
Constraints on Fundamental Cosmological Parameters with Upcoming Epoch of Reionization Observations
122792689
Computer animation of extensive air showers interacting with the MILAGRO water Cherenkov detector
I employ advanced computer animation to visualize the interaction of Extensive Air Showers (EAS) with the Milagro water reservoir. The animations help conceptualize the evolution of the EAS particle front as it hits a large volume of water and converts to a front of Cherenkov photons. Expected effects such as refraction and curvature are easily seen, as well as a number of novel behaviors. A simple model that explains the observed dynamics of the shower front is presented.
1554579
Rapid Notification of TeV Transients with the Milagro Telescope
The Milagro telescope is a wide field of view TeV observatory that is ideally suited for the observation of transients in the 300 GeV–10 TeV band. Milagro has a very large field of view (about 2 sr), nearly continuous operation, and a fluence sensitivity that is comparable to satellite experiments. Milagro is currently performing real time searches for TeV transients, with the goal of prompt notification and multi‐wavelength observation of any detected TeV transients.
118490778
FOUR FUNDAMENTAL FOREGROUND POWER SPECTRUM SHAPES FOR 21 cm COSMOLOGY OBSERVATIONS
Contamination from instrumental effects interacting with bright astrophysical sources is the primary impediment to measuring Epoch of Reionization (EoR) and Baryon Acoustic Oscillations (BAO) 21 cm power spectra—an effect called mode mixing. In this paper, we identify four fundamental power spectrum shapes produced by mode mixing that will affect all upcoming observations. We are able, for the first time, to explain the wedge-like structure seen in advanced simulations and to forecast the shape of an "EoR window" that is mostly free of contamination. Understanding the origins of these contaminations also enables us to identify calibration and foreground subtraction errors below the imaging limit, providing a powerful new tool for precision observations.
16249880
Performances of 4-gap timing RPCs for relativistic ions in the range Z=1-6
Results from 4-gap Resistive Plate Chambers (RPCs) under irradiation by fully stripped relativistic ions (normalized momentum p/M = γβ = 2.7, atomic charge Z = 1−6) are presented. A time resolution of 80 ps at high efficiency has been obtained by using standard `off the shelf' 4-gap timing RPCs from the new HADES time-of-flight wall. The resolution worsened to 100 ps for ~ 1 kHz/cm2 proton flux and for ~ 100 Hz/cm2 carbon flux. The chambers were operated at a field E = 100 kV/cm, showing a high stability during the measurements. It seems to exist ample room for improvement, in particular regarding the time resolution.
120073980
Analysis of compact and sealed RPCs feasibility
In this article, the feasibility of developing compact and portable float glass sealed Resistive Plate Chambers, sRPCs, is analyzed. For this purpose, several small (80 cm 2 ) sealed chambers have been constructed using inexpensive materials like windows float glass, copper tape and nylon fishing line. For the sake of simplicity, during this first development stage, only R134a has been used as ionizing gas. In order to distinguish gas leakage from internal gas degradation, a couple of sRPCs were tested inside a box with flowing gas: one with R134a and another with N2. Prompt charge, signal rising slope and operational current were used to assess chambers performance degradation during a two-week period. Regarding these variables, small leakages were spotted as the main reason for the performance degradation observed after about one week of steady operation at the sRPC working in N2 environment. The sRPC working in an R134a environment did not show any significative degradation during the whole test. A discussion on merits and limitations of the proposed design is provided.