Permittivity and permeability of epoxy-magnetite powder composites at microwave frequencies

Radio, millimetre and sub-millimetre astronomy experiments as well as remote sensing applications often require castable absorbers with well known electromagnetic properties to design and realize calibration targets. In this context, we fabricated and characterized two samples using different ratios of two easily commercially available materials: epoxy (Stycast 2850FT) and magnetite ($\mathrm{Fe_{3}O_{4}}$) powder. We performed transmission and reflection measurements from 7 GHz up to 170 GHz with a VNA equipped with a series of standard horn antennas. Using an empirical model we analysed the data to extract complex permittivity and permeability from transmission data; then we used reflection data to validate the results. In this paper we present the sample fabrication procedure, analysis method, parameter extraction pipeline, and results for two samples with different epoxy-powder mass ratios.Comment: 7 pages, 18 figures, submitted to the Journal of Applied Physics (AIP

Impact of half-wave plate systematics on the measurement of CMB BB-mode polarization

Polarization of the cosmic microwave background (CMB) can help probe the fundamental physics behind cosmic inflation via the measurement of primordial $B$ modes. As this requires exquisite control over instrumental systematics, some next-generation CMB experiments plan to use a rotating half-wave plate (HWP) as polarization modulator. However, the HWP non-idealities, if not properly treated in the analysis, can result in additional systematics. In this paper, we present a simple, semi-analytical end-to-end model to propagate the HWP non-idealities through the macro-steps that make up any CMB experiment (observation of multi-frequency maps, foreground cleaning, and power spectra estimation) and compute the HWP-induced bias on the estimated tensor-to-scalar ratio, $r$. We find that the effective polarization efficiency of the HWP suppresses the polarization signal, leading to an underestimation of $r$. Laboratory measurements of the properties of the HWP can be used to calibrate this effect, but we show how gain calibration of the CMB temperature can also be used to partially mitigate it. On the basis of our findings, we present a set of recommendations for the HWP design that can help maximize the benefits of gain calibration.Comment: 17 pages + appendices and bibliography, 7 figures, 1 table; submitted to JCA

The Density Profiles of Massive, Relaxed Galaxy Clusters. II. Separating Luminous and Dark Matter in Cluster Cores

We present stellar and dark matter (DM) density profiles for a sample of seven massive, relaxed galaxy clusters derived from strong and weak gravitational lensing and resolved stellar kinematic observations within the centrally-located brightest cluster galaxies (BCGs). In Paper I of the series, we demonstrated that the total density profile derived from these data, which span 3 decades in radius, is consistent with numerical DM-only simulations at radii >~ 5-10 kpc, despite the significant contribution of stellar material in the core. Here we decompose the inner mass profiles of these clusters into stellar and dark components. Parametrizing the DM density profile as a power law rho_DM ~ r^{-\beta} on small scales, we find a mean slope = 0.50 +- 0.10 (random) +0.14-0.13 (systematic). Alternatively, cored Navarro-Frenk-White (NFW) profiles with = 1.14 +- 0.13 (random) +0.14-0.22 (systematic) provide an equally good description. These density profiles are significantly shallower than canonical NFW models at radii <~ 30 kpc, comparable to the effective radii of the BCGs. The inner DM profile is correlated with the distribution of stars in the BCG, suggesting a connection between the inner halo and the assembly of stars in the central galaxy. The stellar mass-to-light ratio inferred from lensing and stellar dynamics is consistent with that inferred using stellar population synthesis models if a Salpeter initial mass function is adopted. We compare these results to theories describing the interaction between baryons and DM in cluster cores, including adiabatic contraction models and the possible effects of galaxy mergers and active galactic nucleus feedback, and evaluate possible signatures of alternative DM candidates.Comment: Updated to matched the published version in Ap

The STRIP instrument of the Large Scale Polarization Explorer: microwave eyes to map the Galactic polarized foregrounds

In this paper we discuss the latest developments of the STRIP instrument of the "Large Scale Polarization Explorer" (LSPE) experiment. LSPE is a novel project that combines ground-based (STRIP) and balloon-borne (SWIPE) polarization measurements of the microwave sky on large angular scales to attempt a detection of the "B-modes" of the Cosmic Microwave Background polarization. STRIP will observe approximately 25% of the Northern sky from the "Observatorio del Teide" in Tenerife, using an array of forty-nine coherent polarimeters at 43 GHz, coupled to a 1.5 m fully rotating crossed-Dragone telescope. A second frequency channel with six-elements at 95 GHz will be exploited as an atmospheric monitor. At present, most of the hardware of the STRIP instrument has been developed and tested at sub-system level. System-level characterization, starting in July 2018, will lead STRIP to be shipped and installed at the observation site within the end of the year. The on-site verification and calibration of the whole instrument will prepare STRIP for a 2-years campaign for the observation of the CMB polarization.Comment: 17 pages, 15 figures, proceedings of the SPIE Astronomical Telescopes + Instrumentation conference "Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy IX", on June 15th, 2018, Austin (TX

Simulations of systematic effects arising from cosmic rays in the LiteBIRD space telescope, and effects on the measurements of CMB B-modes

International audienceSystematic effects arising from cosmic rays have been shown to be a significant threat to space telescopes using high-sensitivity bolometers. The LiteBIRD space mission aims to measure the polarised Cosmic Microwave Background with unprecedented sensitivity, but its positioning in space will also render it susceptible to cosmic ray effects. We present an end-to-end simulator for evaluating the expected scale of cosmic ray effects on the LiteBIRD space mission, which we demonstrate on a subset of detectors on the 166 GHz band of the Low Frequency Telescope. The simulator couples the expected proton flux at L2 with a model of the thermal response of the LFT focal plane and the electrothermal response of its superconducting detectors, producing time-ordered data which is projected into simulated sky maps and subsequent angular power spectra