arXiv subjects

J. M. Kovac

Publications and source records attributed to J. M. Kovac.

82 records · Page 5Linked to original sources

arXiv2011

The Keck Array: a pulse tube cooled CMB polarimeter

The Keck Array is a cosmic microwave background (CMB) polarimeter that will begin observing from the South Pole in late 2010. The initial deployment will consist of three telescopes similar to BICEP2 housed in ultra-compact, pulse tube cooled cryostats. Two more receivers will be added the following year. In these proceedings we report on the design and performance of the Keck cryostat. We also report some initial results on the performance of antenna-coupled TES detectors operating in the presence of a pulse tube. We find that the performance of the detectors is not seriously impacted by the replacement of BICEP2's liquid helium cryostat with a pulse tube cooled cryostat.

astro-ph.IM↗

arXiv2011

A Millimeter-Wave Galactic Plane Survey With The BICEP Polarimeter

In addition to its potential to probe the Inflationary cosmological paradigm, millimeter-wave polarimetry is a powerful tool for studying the Milky Way galaxy's composition and magnetic field structure. Towards this end, presented here are Stokes I, Q, and U maps of the Galactic plane from the millimeter-wave polarimeter BICEP covering the Galactic longitude range 260 - 340 degrees in three atmospheric transmission windows centered on 100, 150, and 220 GHz. The maps sample an optical depth 1 < AV < 30, and are consistent with previous characterizations of the Galactic millimeter-wave frequency spectrum and the large-scale magnetic field structure permeating the interstellar medium. Polarized emission is detected over the entire region within two degrees of the Galactic plane and indicates that the large-scale magnetic field is oriented parallel to the plane of the Galaxy. An observed trend of decreasing polarization fraction with increasing total intensity rules out the simplest model of a constant Galactic magnetic field throughout the Galaxy. Including WMAP data in the analysis, the degree-scale frequency spectrum of Galactic polarization fraction is plotted between 23 and 220 GHz for the first time. A generally increasing trend of polarization fraction with electromagnetic frequency is found, which varies from 0.5%-1.5%at frequencies below 50 GHz to 2.5%-3.5%above 90 GHz. The BICEP and WMAP data are fit to a two-component (synchrotron and dust) model showing that the higher frequency BICEP data are necessary to tightly constrain the amplitude and spectral index of Galactic dust. Furthermore, the dust amplitude predicted by this two-component fit is consistent with model predictions of dust emission in the BICEP bands.

astro-ph.GA↗

arXiv2010

Antenna-coupled TES Bolometer Arrays for BICEP2/Keck and SPIDER

BICEP2/Keck and SPIDER are cosmic microwave background (CMB) polarimeters targeting the B-mode polarization induced by primordial gravitational waves from inflation. They will be using planar arrays of polarization sensitive antenna-coupled TES bolometers, operating at frequencies between 90 GHz and 220 GHz. At 150 GHz each array consists of 64 polarimeters and four of these arrays are assembled together to make a focal plane, for a total of 256 dual-polarization elements (512 TES sensors). The detector arrays are integrated with a time-domain SQUID multiplexer developed at NIST and read out using the multi-channels electronics (MCE) developed at the University of British Columbia. Following our progress in improving detector parameters uniformity across the arrays and fabrication yield, our main effort has focused on improving detector arrays optical and noise performances, in order to produce science grade focal planes achieving target sensitivities. We report on changes in detector design implemented to optimize such performances and following focal plane arrays characterization. BICEP2 has deployed a first 150 GHz science grade focal plane to the South Pole in December 2009.

astro-ph.IM↗

arXiv2010

Measurement of Cosmic Microwave Background Polarization Power Spectra from Two Years of BICEP Data

Background Imaging of Cosmic Extragalactic Polarization (BICEP) is a bolometric polarimeter designed to measure the inflationary B-mode polarization of the cosmic microwave background (CMB) at degree angular scales. During three seasons of observing at the South Pole (2006 through 2008), BICEP mapped ~2% of the sky chosen to be uniquely clean of polarized foreground emission. Here we present initial results derived from a subset of the data acquired during the first two years. We present maps of temperature, Stokes Q and U, E and B modes, and associated angular power spectra. We demonstrate that the polarization data are self-consistent by performing a series of jackknife tests. We study potential systematic errors in detail and show that they are sub-dominant to the statistical errors. We measure the E-mode angular power spectrum with high precision at 21 < ell < 335, detecting for the first time the peak expected at ell ~ 140. The measured E-mode spectrum is consistent with expectations from a LCDM model, and the B-mode spectrum is consistent with zero. The tensor-to-scalar ratio derived from the B-mode spectrum is r = 0.03+0.31-0.26, or r < 0.72 at 95% confidence, the first meaningful constraint on the inflationary gravitational wave background to come directly from CMB B-mode polarization.

astro-ph.CO↗

arXiv2010

Characterization of the BICEP Telescope for High-Precision Cosmic Microwave Background Polarimetry

The BICEP experiment was designed specifically to search for the signature of inflationary gravitational waves in the polarization of the cosmic microwave background (CMB). Using a novel small-aperture refractor and 49 pairs of polarization-sensitive bolometers, BICEP has completed 3 years of successful observations at the South Pole beginning in 2006 February. To constrain the amplitude of the inflationary B-mode polarization, which is expected to be at least 7 orders of magnitude fainter than the 3 K CMB intensity, precise control of systematic effects is essential. This paper describes the characterization of potential systematic errors for the BICEP experiment, supplementing a companion paper on the initial cosmological results. Using the analysis pipelines for the experiment, we have simulated the impact of systematic errors on the B-mode polarization measurement. Guided by these simulations, we have established benchmarks for the characterization of critical instrumental properties including bolometer relative gains, beam mismatch, polarization orientation, telescope pointing, sidelobes, thermal stability, and timestream noise model. A comparison of the benchmarks with the measured values shows that we have characterized the instrument adequately to ensure that systematic errors do not limit BICEP's 2-year results, and identifies which future refinements are likely necessary to probe inflationary B-mode polarization down to levels below a tensor-to-scalar ratio r = 0.1.

astro-ph.CO↗

arXiv2007

CMB from the South Pole: Past, Present, and Future

South Pole Station offers a unique combination of high, dry, stable conditions and well-developed support facilities. Over the past 20 years, a sequence of increasingly sophisticated CMB experiments at Pole have built on the experience of early pioneering efforts, producing a number of landmark contributions to the field. Telescopes at the South Pole were among the first to make repeated detections of degree-scale CMB temperature anisotropy and to map out the harmonic structure of its acoustic peaks. More recent achievements include the first detection of polarization of the CMB and the most precise measurements of the temperature power spectrum at small angular scales. New CMB telescopes at the South Pole are now making ultra-deep observations of the large-scale polarization of the CMB and of its secondary temperature anisotropies on arcminute scales. These two observing goals represent the current frontiers of CMB research, focused on constraining Inflation and the nature of Dark Energy. The South Pole now hosts an array of CMB observing platforms covering a wide range of angular scales and supporting very long integration times on the cleanest sky available, and thus should play an increasing role in pushing these frontiers of CMB research.

astro-ph↗

arXiv2006

The Robinson Gravitational Wave Background Telescope (BICEP): a bolometric large angular scale CMB polarimeter

The Robinson Telescope (BICEP) is a ground-based millimeter-wave bolometric array designed to study the polarization of the cosmic microwave background radiation (CMB) and galactic foreground emission. Such measurements probe the energy scale of the inflationary epoch, tighten constraints on cosmological parameters, and verify our current understanding of CMB physics. Robinson consists of a 250-mm aperture refractive telescope that provides an instantaneous field-of-view of 17 degrees with angular resolution of 55 and 37 arcminutes at 100 GHz and 150 GHz, respectively. Forty-nine pair of polarization-sensitive bolometers are cooled to 250 mK using a 4He/3He/3He sorption fridge system, and coupled to incoming radiation via corrugated feed horns. The all-refractive optics is cooled to 4 K to minimize polarization systematics and instrument loading. The fully steerable 3-axis mount is capable of continuous boresight rotation or azimuth scanning at speeds up to 5 deg/s. Robinson has begun its first season of observation at the South Pole. Given the measured performance of the instrument along with the excellent observing environment, Robinson will measure the E-mode polarization with high sensitivity, and probe for the B-modes to unprecedented depths. In this paper we discuss aspects of the instrument design and their scientific motivations, scanning and operational strategies, and the results of initial testing and observations.

astro-ph↗

arXiv2004

Polarization Observations with the Cosmic Background Imager

Polarization observations of the cosmic microwave background with the Cosmic Background Imager from September 2002 to May 2004 provide a significant detection of the E-mode polarization and reveal an angular power spectrum of polarized emission showing peaks and valleys that are shifted in phase by half a cycle relative to those of the total intensity spectrum. This key agreement between the phase of the observed polarization spectrum and that predicted based on the total intensity spectrum provides support for the standard model of cosmology, in which dark matter and dark energy are the dominant constituents, the geometry is close to flat, and primordial density fluctuations are predominantly adiabatic with a matter power spectrum commensurate with inflationary cosmological models.

astro-ph↗

arXiv2004

DASI Three-Year Cosmic Microwave Background Polarization Results

We present the analysis of the complete 3-year data set obtained with the Degree Angular Scale Interferometer (DASI) polarization experiment, operating from the Amundsen-Scott South Pole research station. Additional data obtained at the end of the 2002 Austral winter and throughout the 2003 season were added to the data from which the first detection of polarization of the cosmic microwave background radiation was reported. The analysis of the combined data supports, with increased statistical power, all of the conclusions drawn from the initial data set. In particular, the detection of E-mode polarization is increased to 6.3 sigma confidence level, TE cross-polarization is detected at 2.9 sigma, and B-mode polarization is consistent with zero, with an upper limit well below the level of the detected E-mode polarization. The results are in excellent agreement with the predictions of the cosmological model that has emerged from CMB temperature measurements. The analysis also demonstrates that contamination of the data by known sources of foreground emission is insignificant.

astro-ph↗

arXiv2002

Measuring Polarization with DASI

We describe an experiment to measure the polarization of the Cosmic Microwave Background (CMB) with the Degree Angular Scale Interferometer (DASI), a compact microwave interferometer optimized to detect CMB anisotropy at multipoles 140 to 900. The telescope has operated at the Amundsen-Scott South Pole research station since 2000 January. The telescope was retrofit as a polarimeter during the 2000--2001 austral summer, and throughout the 2001 and 2002 austral winters has made observations of the CMB with sensitivity to all four Stokes parameters. The telescope performance has been extensively characterized through observations of artificial sources, the Moon, and polarized and unpolarized Galactic sources. In 271 days of observation, DASI has differenced the CMB fluctuations in two fields to an rms noise level of 2.8 uK.

astro-ph↗