arXiv subjects

K. L. Thompson

Publications and source records attributed to K. L. Thompson.

At least 91 records · Page 5Linked to original sources

arXiv2016

Initial Performance of BICEP3: A Degree Angular Scale 95 GHz Band Polarimeter

BICEP3 is a $550~mm$ aperture telescope with cold, on-axis, refractive optics designed to observe at the $95~GHz$ band from the South Pole. It is the newest member of the BICEP/Keck family of inflationary probes specifically designed to measure the polarization of the cosmic microwave background (CMB) at degree-angular scales. BICEP3 is designed to house 1280 dual-polarization pixels, which, when fully-populated, totals to $\sim$9$\times$ the number of pixels in a single Keck $95~GHz$ receiver, thus further advancing the BICEP/Keck program's $95~GHz$ mapping speed. BICEP3 was deployed during the austral summer of 2014-2015 with 9 detector tiles, to be increased to its full capacity of 20 in the second season. After instrument characterization measurements were taken, CMB observation commenced in April 2015. Together with multi-frequency observation data from Planck, BICEP2, and the Keck Array, BICEP3 is projected to set upper limits on the tensor-to-scalar ratio to $r$ $\lesssim 0.03$ at $95\%$ C.L..

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arXiv2015

BICEP2 / Keck Array V: Measurements of B-mode Polarization at Degree Angular Scales and 150 GHz by the Keck Array

The Keck Array is a system of cosmic microwave background (CMB) polarimeters, each similar to the BICEP2 experiment. In this paper we report results from the 2012 and 2013 observing seasons, during which the Keck Array consisted of five receivers all operating in the same (150 GHz) frequency band and observing field as BICEP2. We again find an excess of B-mode power over the lensed-$Λ$CDM expectation of $> 5 σ$ in the range $30 < \ell < 150$ and confirm that this is not due to systematics using jackknife tests and simulations based on detailed calibration measurements. In map difference and spectral difference tests these new data are shown to be consistent with BICEP2. Finally, we combine the maps from the two experiments to produce final Q and U maps which have a depth of 57 nK deg (3.4 $μ$K arcmin) over an effective area of 400 deg$^2$ for an equivalent survey weight of 250,000 $μ$K$^{-2}$. The final BB band powers have noise uncertainty a factor of 2.3 times better than the previous results, and a significance of detection of excess power of $> 6σ$.

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arXiv2015

The Q/U Imaging ExperimenT: Polarization Measurements of the Galactic Plane at 43 and 95 GHz

We present polarization observations of two Galactic plane fields centered on Galactic coordinates (l,b)=(0 deg,0 deg) and (329 deg, 0 deg) at Q- (43 GHz) and W-band (95 GHz), covering between 301 and 539 square degrees depending on frequency and field. These measurements were made with the QUIET instrument between 2008 October and 2010 December, and include a total of 1263 hours of observations. The resulting maps represent the deepest large-area Galactic polarization observations published to date at the relevant frequencies with instrumental rms noise varying between 1.8 and 2.8 uK deg, 2.3-6 times deeper than corresponding WMAP and Planck maps. The angular resolution is 27.3' and 12.8' FWHM at Q- and W-band, respectively. We find excellent agreement between the QUIET and WMAP maps over the entire fields, and no compelling evidence for significant residual instrumental systematic errors in either experiment, whereas the Planck 44 GHz map deviates from these in a manner consistent with reported systematic uncertainties for this channel. We combine QUIET and WMAP data to compute inverse-variance-weighted average maps, effectively retaining small angular scales from QUIET and large angular scales from WMAP. From these combined maps, we derive constraints on several important astrophysical quantities, including a robust detection of polarized synchrotron spectral index steepening of ~0.2 off the plane, as well as the Faraday rotation measure toward the Galactic center (RM=-4000 +/- 200 rad m^-2), all of which are consistent with previously published results. Both the raw QUIET and the co-added QUIET+WMAP maps are made publicly available together with all necessary ancillary information.

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arXiv2014

The Q/U Imaging Experiment: Polarization Measurements of Radio Sources at 43 and 95 GHz

We present polarization measurements of extragalactic radio sources observed during the Cosmic Microwave Background polarization survey of the Q/U Imaging Experiment (QUIET), operating at 43 GHz (Q-band) and 95 GHz (W-band). We examine sources selected at 20 GHz from the public, $>$40 mJy catalog of the Australia Telescope (AT20G) survey. There are $\sim$480 such sources within QUIET's four low-foreground survey patches, including the nearby radio galaxies Centaurus A and Pictor A. The median error on our polarized flux density measurements is 30--40 mJy per Stokes parameter. At S/N $> 3$ significance, we detect linear polarization for seven sources in Q-band and six in W-band; only $1.3 \pm 1.1$ detections per frequency band are expected by chance. For sources without a detection of polarized emission, we find that half of the sources have polarization amplitudes below 90 mJy (Q-band) and 106 mJy (W-band), at 95% confidence. Finally, we compare our polarization measurements to intensity and polarization measurements of the same sources from the literature. For the four sources with WMAP and Planck intensity measurements $>1$ Jy, the polarization fraction are above 1% in both QUIET bands. At high significance, we compute polarization fractions as much as 10--20% for some sources, but the effects of source variability may cut that level in half for contemporaneous comparisons. Our results indicate that simple models---ones that scale a fixed polarization fraction with frequency---are inadequate to model the behavior of these sources and their contributions to polarization maps.

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arXiv2014

Large-area Reflective Infrared Filters for Millimeter/sub-mm Telescopes

Ground-based millimeter and sub-millimeter telescopes are attempting to image the sky with ever-larger cryogenically-cooled bolometer arrays, but face challenges in mitigating the infrared loading accompanying large apertures. Absorptive infrared filters supported by mechanical coolers scale insufficiently with aperture size. Reflective metal-mesh filters placed behind the telescope window provide a scalable solution in principle, but have been limited by photolithography constraints to diameters under 300 mm. We present laser etching as an alternate technique to photolithography for fabrication of large-area reflective filters, and show results from lab tests of 500 mm-diameter filters. Filters with up to 700 mm diameter can be fabricated using laser etching with existing capability.

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arXiv2014

BICEP3: a 95 GHz refracting telescope for degree-scale CMB polarization

BICEP3 is a 550 mm-aperture refracting telescope for polarimetry of radiation in the cosmic microwave background at 95 GHz. It adopts the methodology of BICEP1, BICEP2 and the Keck Array experiments - it possesses sufficient resolution to search for signatures of the inflation-induced cosmic gravitational-wave background while utilizing a compact design for ease of construction and to facilitate the characterization and mitigation of systematics. However, BICEP3 represents a significant breakthrough in per-receiver sensitivity, with a focal plane area 5$\times$ larger than a BICEP2/Keck Array receiver and faster optics ($f/1.6$ vs. $f/2.4$). Large-aperture infrared-reflective metal-mesh filters and infrared-absorptive cold alumina filters and lenses were developed and implemented for its optics. The camera consists of 1280 dual-polarization pixels; each is a pair of orthogonal antenna arrays coupled to transition-edge sensor bolometers and read out by multiplexed SQUIDs. Upon deployment at the South Pole during the 2014-15 season, BICEP3 will have survey speed comparable to Keck Array 150 GHz (2013), and will significantly enhance spectral separation of primordial B-mode power from that of possible galactic dust contamination in the BICEP2 observation patch.

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arXiv2014

SPT-3G: A Next-Generation Cosmic Microwave Background Polarization Experiment on the South Pole Telescope

We describe the design of a new polarization sensitive receiver, SPT-3G, for the 10-meter South Pole Telescope (SPT). The SPT-3G receiver will deliver a factor of ~20 improvement in mapping speed over the current receiver, SPTpol. The sensitivity of the SPT-3G receiver will enable the advance from statistical detection of B-mode polarization anisotropy power to high signal-to-noise measurements of the individual modes, i.e., maps. This will lead to precise (~0.06 eV) constraints on the sum of neutrino masses with the potential to directly address the neutrino mass hierarchy. It will allow a separation of the lensing and inflationary B-mode power spectra, improving constraints on the amplitude and shape of the primordial signal, either through SPT-3G data alone or in combination with BICEP-2/KECK, which is observing the same area of sky. The measurement of small-scale temperature anisotropy will provide new constraints on the epoch of reionization. Additional science from the SPT-3G survey will be significantly enhanced by the synergy with the ongoing optical Dark Energy Survey (DES), including: a 1% constraint on the bias of optical tracers of large-scale structure, a measurement of the differential Doppler signal from pairs of galaxy clusters that will test General Relativity on ~200 Mpc scales, and improved cosmological constraints from the abundance of clusters of galaxies.

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arXiv2013

Second Season QUIET Observations: Measurements of the CMB Polarization Power Spectrum at 95 GHz

The Q/U Imaging ExperimenT (QUIET) has observed the cosmic microwave background (CMB) at 43 and 95GHz. The 43-GHz results have been published in QUIET Collaboration et al. (2011), and here we report the measurement of CMB polarization power spectra using the 95-GHz data. This data set comprises 5337 hours of observations recorded by an array of 84 polarized coherent receivers with a total array sensitivity of 87 uK sqrt(s). Four low-foreground fields were observed, covering a total of ~1000 square degrees with an effective angular resolution of 12.8', allowing for constraints on primordial gravitational waves and high-signal-to-noise measurements of the E-modes across three acoustic peaks. The data reduction was performed using two independent analysis pipelines, one based on a pseudo-Cl (PCL) cross-correlation approach, and the other on a maximum-likelihood (ML) approach. All data selection criteria and filters were modified until a predefined set of null tests had been satisfied before inspecting any non-null power spectrum. The results derived by the two pipelines are in good agreement. We characterize the EE, EB and BB power spectra between l=25 and 975 and find that the EE spectrum is consistent with LCDM, while the BB power spectrum is consistent with zero. Based on these measurements, we constrain the tensor-to-scalar ratio to r=1.1+0.9-0.8 (r<2.8 at 95% C.L.) as derived by the ML pipeline, and r=1.2+0.9-0.8 (r<2.7 at 95% C.L.) as derived by the PCL pipeline. In one of the fields, we find a correlation with the dust component of the Planck Sky Model, though the corresponding excess power is small compared to statistical errors. Finally, we derive limits on all known systematic errors, and demonstrate that these correspond to a tensor-to-scalar ratio smaller than r=0.01, the lowest level yet reported in the literature.

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arXiv2012

The QUIET Instrument

The Q/U Imaging ExperimenT (QUIET) is designed to measure polarization in the Cosmic Microwave Background, targeting the imprint of inflationary gravitational waves at large angular scales (~ 1 degree). Between 2008 October and 2010 December, two independent receiver arrays were deployed sequentially on a 1.4 m side-fed Dragonian telescope. The polarimeters which form the focal planes use a highly compact design based on High Electron Mobility Transistors (HEMTs) that provides simultaneous measurements of the Stokes parameters Q, U, and I in a single module. The 17-element Q-band polarimeter array, with a central frequency of 43.1 GHz, has the best sensitivity (69 uK sqrt(s)) and the lowest instrumental systematic errors ever achieved in this band, contributing to the tensor-to-scalar ratio at r < 0.1. The 84-element W-band polarimeter array has a sensitivity of 87 uK sqrt(s) at a central frequency of 94.5 GHz. It has the lowest systematic errors to date, contributing at r < 0.01. The two arrays together cover multipoles in the range l= 25-975. These are the largest HEMT-based arrays deployed to date. This article describes the design, calibration, performance of, and sources of systematic error for the instrument.

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arXiv2012

First Season QUIET Observations: Measurements of CMB Polarization Power Spectra at 43 GHz in the Multipole Range 25 <= ell <= 475

The Q/U Imaging ExperimenT (QUIET) employs coherent receivers at 43GHz and 95GHz, operating on the Chajnantor plateau in the Atacama Desert in Chile, to measure the anisotropy in the polarization of the CMB. QUIET primarily targets the B modes from primordial gravitational waves. The combination of these frequencies gives sensitivity to foreground contributions from diffuse Galactic synchrotron radiation. Between 2008 October and 2010 December, >10,000hours of data were collected, first with the 19-element 43GHz array (3458hours) and then with the 90-element 95GHz array. Each array observes the same four fields, selected for low foregrounds, together covering ~1000deg^2. This paper reports initial results from the 43GHz receiver which has an array sensitivity to CMB fluctuations of 69uK sqrt(s). The data were extensively studied with a large suite of null tests before the power spectra, determined with two independent pipelines, were examined. Analysis choices, including data selection, were modified until the null tests passed. Cross correlating maps with different telescope pointings is used to eliminate a bias. This paper reports the EE, BB and EB power spectra in the multipole range ell=25-475. With the exception of the lowest multipole bin for one of the fields, where a polarized foreground, consistent with Galactic synchrotron radiation, is detected with 3sigma significance, the E-mode spectrum is consistent with the LCDM model, confirming the only previous detection of the first acoustic peak. The B-mode spectrum is consistent with zero, leading to a measurement of the tensor-to-scalar ratio of r=0.35+1.06-0.87. The combination of a new time-stream double-demodulation technique, Mizuguchi-Dragone optics, natural sky rotation, and frequent boresight rotation leads to the lowest level of systematic contamination in the B-mode power so far reported, below the level of r=0.1

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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.

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arXiv2010

The QUaD Galactic Plane Survey 1: Maps And Analysis of Diffuse Emission

We present a survey of ~800 square degrees of the galactic plane observed with the QUaD telescope. The primary product of the survey are maps of Stokes I, Q and U parameters at 100 and 150 GHz, with spatial resolution 5 and 3.5 arcminutes respectively. Two regions are covered, spanning approximately 245-295 and 315-5 degrees in galactic longitude l, and -4<b<+4 degrees in galactic latitude b. At 0.02 degree square pixel size, the median sensitivity is 74 and 107 kJy/sr at 100 GHz and 150 GHz respectively in I, and 98 and 120 kJy/sr for Q and U. In total intensity, we find an average spectral index of 2.35+/-0.01 (stat) +/- 0.02 (sys) for |b|<1 degree, indicative of emission components other than thermal dust. A comparison to published dust, synchrotron and free-free models implies an excess of emission in the 100 GHz QUaD band, while better agreement is found at 150 GHz. A smaller excess is observed when comparing QUaD 100 GHz data to WMAP 5-year W band; in this case the excess is likely due to the wider bandwidth of QUaD. Combining the QUaD and WMAP data, a two-component spectral fit to the inner galactic plane (|b|<1 degree) yields mean spectral indices of -0.32 +/- 0.03 and 2.84 +/- 0.03; the former is interpreted as a combination of the spectral indices of synchrotron, free-free and dust, while the second is attributed largely to the thermal dust continuum. In the same galactic latitude range, the polarization data show a high degree of alignment perpendicular to the expected galactic magnetic field direction, and exhibit mean polarization fraction 1.38+/-0.08 (stat) +/-0.1 (sys) % at 100 GHz and 1.70 +/- 0.06 (stat) +/- 0.1 (sys) % at 150GHz. We find agreement in polarization fraction between QUaD 100 GHz and WMAP W band, the latter giving 1.1 +/- 0.4 %.

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arXiv2010

The QUaD Galactic Plane Survey II: A Compact Source Catalog

We present a catalog of compact sources derived from the QUaD Galactic Plane Survey. The survey covers ~800 square degrees of the inner galaxy (|b|<4 degrees) in Stokes I, Q and U parameters at 100 and 150 GHz, with angular resolution 5 and 3.5 arcminutes. 505 unique sources are identified in I, of which 239 are spatially matched between frequency bands, with 50 (216) detected at 100 (150) GHz alone; 182 sources are identified as ultracompact HII (UCHII) regions. Approximating the distribution of total intensity source fluxes as a power-law, we find a slope of $γ_{S,100}=-1.8\pm0.4$ at 100 GHz, and $γ_{S,150}=-2.2\pm0.4$ at 150 GHz. Similarly, the power-law index of the source two-point angular correlation function is $γ_{θ,100}=-1.21\pm0.04$ and $γ_{θ,150}=-1.25\pm0.04$. The total intensity spectral index distribution peaks at $α_{I}\sim0.25$, indicating that dust emission is not the only source of radiation produced by these objects between 100 and 150 GHz; free-free radiation is likely significant in the 100 GHz band. Four sources are detected in polarized intensity P, of which three have matching counterparts in I. Three of the polarized sources lie close to the galactic center, Sagittarius A*, Sagittarius B2 and the Galactic Radio Arc, while the fourth is RCW 49, a bright HII region. An extended polarized source, undetected by the source extraction algorithm on account of its $\sim0.5^{\circ}$ size, is identified visually, and is an isolated example of large-scale polarized emission oriented distinctly from the bulk galactic dust polarization.

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arXiv2010

Characterization of the Millimeter-Wave Polarization of Centaurus A with QUaD

Centaurus (Cen) A represents one of the best candidates for an isolated, compact, highly polarized source that is bright at typical cosmic microwave background (CMB) experiment frequencies. We present measurements of the 4 degree by 2 degree region centered on Cen A with QUaD, a CMB polarimeter whose absolute polarization angle is known to 0.5 degrees. Simulations are performed to assess the effect of misestimation of the instrumental parameters on the final measurement and systematic errors due to the field's background structure and temporal variability from Cen A's nuclear region are determined. The total (Q, U) of the inner lobe region is (1.00 +/- 0.07 (stat.) +/- 0.04 (sys.), -1.72 +/- 0.06 +/- 0.05) Jy at 100 GHz and (0.80 +/- 0.06 +/- 0.06, -1.40 +/- 0.07 +/- 0.08) Jy at 150 GHz, leading to polarization angles and total errors of -30.0 +/- 1.1 degrees and -29.1 +/- 1.7 degrees. These measurements will allow the use of Cen A as a polarized calibration source for future millimeter experiments.

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arXiv2010

Parameter Estimation from Improved Measurements of the CMB from QUaD

We evaluate the contribution of cosmic microwave background (CMB) polarization spectra to cosmological parameter constraints. We produce cosmological parameters using high-quality CMB polarization data from the ground-based QUaD experiment and demonstrate for the majority of parameters that there is significant improvement on the constraints obtained from satellite CMB polarization data. We split a multi-experiment CMB dataset into temperature and polarization subsets and show that the best-fit confidence regions for the LCDM 6-parameter cosmological model are consistent with each other, and that polarization data reduces the confidence regions on all parameters. We provide the best limits on parameters from QUaD EE/BB polarization data and we find best-fit parameters from the multi-experiment CMB dataset using the optimal pivot scale of k_p=0.013 Mpc-1 to be {omch2, ombh2, H_0, A_s, n_s, tau}= {0.113, 0.0224, 70.6, 2.29 times 10^-9, 0.960, 0.086}.

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arXiv2009

Improved measurements of the temperature and polarization of the CMB from QUaD

We present an improved analysis of the final dataset from the QUaD experiment. Using an improved technique to remove ground contamination, we double the effective sky area and hence increase the precision of our CMB power spectrum measurements by ~30% versus that previously reported. In addition, we have improved our modeling of the instrument beams and have reduced our absolute calibration uncertainty from 5% to 3.5% in temperature. The robustness of our results is confirmed through extensive jackknife tests and by way of the agreement we find between our two fully independent analysis pipelines. For the standard 6-parameter LCDM model, the addition of QUaD data marginally improves the constraints on a number of cosmological parameters over those obtained from the WMAP experiment alone. The impact of QUaD data is significantly greater for a model extended to include either a running in the scalar spectral index, or a possible tensor component, or both. Adding both the QUaD data and the results from the ACBAR experiment, the uncertainty in the spectral index running is reduced by ~25% compared to WMAP alone, while the upper limit on the tensor-to-scalar ratio is reduced from r < 0.48 to r < 0.33 (95% c.l). This is the strongest limit on tensors to date from the CMB alone. We also use our polarization measurements to place constraints on parity violating interactions to the surface of last scattering, constraining the energy scale of Lorentz violating interactions to < 1.5 x 10^{-43} GeV (68% c.l.). Finally, we place a robust upper limit on the strength of the lensing B-mode signal. Assuming a single flat band power between l = 200 and l = 2000, we constrain the amplitude of B-modes to be < 0.57 micro-K^2 (95% c.l.).

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arXiv2009

Small Angular Scale Measurements of the CMB Temperature Power Spectrum from QUaD

We present measurements of the cosmic microwave background (CMB) radiation temperature anisotropy in the multipole range 2000<ell<3000 from the QUaD telescope's second and third observing seasons. After masking the brightest point sources our results are consistent with the primary LCDM expectation alone. We estimate the contribution of residual (un-masked) radio point sources using a model calibrated to our own bright source observations, and a full simulation of the source finding and masking procedure. Including this contribution slightly improves the chi^2. We also fit a standard SZ template to the bandpowers and see no strong evidence of an SZ contribution, which is as expected for sigma_8 approx 0.8.

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arXiv2009

QUaD: A High-Resolution Cosmic Microwave Background Polarimeter

We describe the QUaD experiment, a millimeter-wavelength polarimeter designed to observe the Cosmic Microwave Background (CMB) from a site at the South Pole. The experiment comprises a 2.64 m Cassegrain telescope equipped with a cryogenically cooled receiver containing an array of 62 polarization-sensitive bolometers. The focal plane contains pixels at two different frequency bands, 100 GHz and 150 GHz, with angular resolutions of 5 arcmin and 3.5 arcmin, respectively. The high angular resolution allows observation of CMB temperature and polarization anisotropies over a wide range of scales. The instrument commenced operation in early 2005 and collected science data during three successive Austral winter seasons of observation.

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