Noise from undetected sources in Dark Energy Survey images

ABSTRACT For ground-based optical imaging with current CCD technology, the Poisson fluctuations in source and sky background photon arrivals dominate the noise budget and are readily estimated. Another component of noise, however, is the signal from the undetected population of stars and galaxies. Using injection of artifical galaxies into images, we demonstrate that the measured variance of galaxy moments (used for weak gravitational lensing measurements) in Dark Energy Survey (DES) images is significantly in excess of the Poisson predictions, by up to 30 per cent, and that the background sky levels are overestimated by current software. By cross-correlating distinct images of ‘empty’ sky regions, we establish that there is a significant image noise contribution from undetected static sources (US), which, on average, are mildly resolved at DES resolution. Treating these US as a stationary noise source, we compute a correction to the moment covariance matrix expected from Poisson noise. The corrected covariance matrix matches the moment variances measured on the injected DES images to within 5 per cent. Thus, we have an empirical method to statistically account for US in weak lensing measurements, rather than requiring extremely deep sky simulations. We also find that local sky determinations can remove most of the bias in flux measurements, at a small penalty in additional, but quantifiable, noise.

Extended search for sub-eV axion-like resonances via four-wave mixing with a quasi-parallel laser collider in a high-quality vacuum system

Resonance states of axion-like particles were searched for via four-wave mixing by focusing two-color pulsed lasers into a quasi-vacuum. A quasi-parallel collision system that allows probing of the sub-eV mass range was realized by focusing the combined laser fields with an off-axis parabolic mirror. A 0.10 mJ/34 fs Ti:sapphire laser pulse and a 0.14 mJ/9 ns Nd:YAG laser pulse were spatiotemporally synchronized by sharing a common optical axis and focused into the vacuum system. No significant four-wave mixing signal was observed at the vacuum pressure of $3.7 \times 10^{-5}$ Pa, thereby providing upper bounds on the coupling-mass relation by assuming exchanges of scalar and pseudoscalar fields at a 95% confidence level in the mass range below 0.21 eV. For this search, the experimental setup was substantially upgraded so that the optical components were compatible with the requirements of the high-quality vacuum system, hence enabling the pulse power to be increased. With the increased pulse power, a new kind of pressure-dependent background photon emerged in addition to the known atomic four-wave mixing process. This paper shows the pressure dependence of these background photons and how to handle them in the search.

Tensioned Metastable Fluid Detectors for Spectrometric Radon–Progeny Detection and AARST-NRPP Standard Qualification

This paper describes how the tensioned metastable fluid detector (TMFD) sensor technology was successfully configured and qualified for efficient, accurate, spectroscopic, and cost-effective radon and progeny spectroscopic detection alongside meeting/exceeding the standards set by the American Association of Radon Scientists and Technologists-National Radon Proficiency Program (AARST-NRPP) Device Evaluation Program (DEP). The DEP represents addressing of a challenging test matrix that assesses a radon collection and measurement device's performance over a variety of functional parameters and environmental conditions. Qualification test conditions covered in this study included performance vetting of the centrifugally tensioned metastable fluid detector (CTMFD) technology under a wide range of temperatures, noncondensing relative humidity (RH) levels, condensing conditions, atmospheric pressures, background photon radiation, nonionizing external electromagnetic (EM) fields, shock and vibration, and air movement. Of all these parameters, only the ambient temperature played a first-order role on radon collection; for this reason, a dynamic compensation algorithm was developed and successfully validated. The remaining AARST-NRPP test parameters were found to have negligible affects. In comparison to state-of-art radon detector systems, the resulting radon specific CTMFD (R-CTMFD) sensor system and protocol are shown to provide for superior sensitivity along with spectroscopic identification of radon–progeny alpha emitters while remaining 100% blind to interfering gamma–beta background radiation.

Characterization of Optical filters using Rutherford Backscattering Spectroscopy

The composition and thickness of optical filters, especially designed for the Auger project, were measured using the RBS method. The aim of this project is to detect the extensive air showers, developed by the interaction of very energetic cosmic rays with the atmospheric air. This swarm of particles, moving at the speed of light through the atmosphere, ionizes the nitrogen atoms, which radiate UV photons in the range of 300-420 nm. This nitrogen fluorescence is subsequently detected by fluorescence detectors having optical filters placed in front of their photomultipliers with high transmittance in the region of 300-420 nm and low transmittance outside this region, in order to maximize the photon signal to background photon ratio. The required transmittance of the optical filters led to specific production techniques, such as the dielectric multi-layer thin film deposition on a substrate, using high-low index UV-transparent materials. In order to select the optimal deposition technique for the mass production of these filters, the RBS method has been used, among others, to provide information concerning the thickness of the individual layers and possible deviations from the desired stoichiometry.The optical filters presented in this work were made of 6 and 12 thin film layers of WOzjMgFi deposited on UV glass. The samples were bombarded with α-particles at EQ — 3MeV, provided by the 5.5 MV Tandem Accelerator at NCSR "Demokritos". The RBS spectra were analyzed utilizing the computer simulation code RUMP.

A new solution to the plasma starved event horizon magnetosphere

Very Long Baseline Interferometry observations at 86 GHz reveal an almost hollow jet in M87 with a forked morphology. The detailed analysis presented here indicates that the spectral luminosity of the central spine of the jet in M87 is a few percent of that of the surrounding hollow jet 200–400 μ as from the central black hole. Furthermore, recent jet models indicate that a hollow “tubular” jet can explain a wide range of plausible broadband spectra originating from jetted plasma located within ~30 μ as of the central black hole, including the 230 GHz correlated flux detected by the Event Horizon Telescope. Most importantly, these hollow jets from the inner accretion flow have an intrinsic power capable of energizing the global jet out to kiloparsec scales. Thus motivated, this paper considers new models of the event horizon magnetosphere (EHM) in low luminosity accretion systems. Contrary to some models, the spine is not an invisible powerful jet. It is an intrinsically weak jet. In the new EHM solution, the accreted poloidal magnetic flux is weak and the background photon field is weak. It is shown how this accretion scenario naturally results in the dissipation of the accreted poloidal magnetic flux in the EHM not the accumulation of poloidal flux required for a powerful jet. The new solution indicates less large scale poloidal magnetic flux (and jet power) in the EHM than in the surrounding accretion flow and cannot support significant EHM driven jets.

Colour vision models: a practical guide, some simulations, and colourvision R package

Human colour vision differs from the vision of other animals. The most obvious differences are the number and type of photoreceptors in the retina. E.g., while humans are insensitive to ultraviolet (UV) light, most non-mammal vertebrates and insects have a colour vision that spans into the UV. The development of colour vision models allowed appraisals of colour vision independent of the human experience. These models are now widespread in ecology and evolution fields. Here I present a guide to colour vision modelling, run a series of simulations, and provide a R package – colourvision – to facilitate the use of colour vision models.I present the mathematical steps for calculation of the most commonly used colour vision models: Chittka (1992) colour hexagon, Endler & Mielke (2005) model, and Vorobyev & Osorio (1998) linear and log-linear receptor noise limited models (RNL). These models are then tested using identical simulated and real data. These comprise of reflectance spectra generated by a logistic function against an achromatic background, achromatic reflectance against an achromatic background, achromatic reflectance against a chromatic background, and real flower reflectance data against a natural background reflectance.When the specific requirements of each model are met, between model results are, overall, qualitatively and quantitatively similar. However, under many common scenarios of colour measurements, models may generate spurious values and/or considerably different predictions. Models that log-transform data and use relative photoreceptor outputs are prone to generate unrealistic results when the stimulus photon catch is smaller than the background photon catch. Moreover, models may generate unrealistic results when the background is chromatic (e.g. leaf reflectance) and the stimulus is an achromatic low reflectance spectrum.Colour vision models are a valuable tool in several ecology and evolution subfields. Nonetheless, knowledge of model assumptions, careful analysis of model outputs, and basic knowledge of calculation behind each model are crucial for appropriate model application, and generation of meaningful and reproducible results. Other aspects of vision not incorporated into these models should be considered when drawing conclusion from model results.

Inflections of Periodicities of Background Photon Spectral Power Densities Are Predicted by the Lorentz Contraction for a Potential Indicator for the Intrinsic Structure of Space

         The value for the Lorentz contraction to produce a discrepancy for a hypothetical number that reflects a property (21.3π4) of sub-matter space was calculated. When applied to time the contraction would be ~35 min. The difference in mass-equivalent energy for an electron at c (the velocity of light in a vacuum) and the required v was ~2 ·10-20 J which has emerged as a significant quantity that may permeate from the force at Planck’s Length when applied across the wavelength of the neutral hydrogen line. Two separate types of photomultiplier instruments (digital and analogue) measuring with different sampling rates for background photon quantities over 50 randomly selected days demonstrated averaged conspicuous inflections of standardized spectral power densities around 35 min. This is the same basic interval where microvariations in the value of the gravitational constant (G) approached a limit at which white noise dominated. The possibility is considered that this value for temporal inflections in photon power spectral densities may reflect the intrinsic nature of space-time contractions that relate gravity and photons.