Peter T. Timbie

Dense magnetized plasma associated with a fast radio burst

Fast radio bursts are bright, unresolved, non-repeating, broadband, millisecond flashes, found primarily at high Galactic latitudes, with dispersion measures much larger than expected for a Galactic source. The inferred all-sky burst rate is comparable to the core-collapse supernova rate out to redshift 0.5. If the observed dispersion measures are assumed to be dominated by the intergalactic medium, the sources are at cosmological distances with redshifts of 0.2 to 1 (refs 10 and 11). These parameters are consistent with a wide range of source models. One fast burst revealed circular polarization of the radio emission, but no linear polarization was detected, and hence no Faraday rotation measure could be determined. Here we report the examination of archival data revealing Faraday rotation in the fast radio burst FRB 110523. Its radio flux and dispersion measure are consistent with values from previously reported bursts and, accounting for a Galactic contribution to the dispersion and using a model of intergalactic electron density, we place the source at a maximum redshift of 0.5. The burst has a much higher rotation measure than expected for this line of sight through the Milky Way and the intergalactic medium, indicating magnetization in the vicinity of the source itself or within a host galaxy. The pulse was scattered by two distinct plasma screens during propagation, which requires either a dense nebula associated with the source or a location within the central region of its host galaxy. The detection in this instance of magnetization and scattering that are both local to the source favours models involving young stellar populations such as magnetars over models involving the mergers of older neutron stars, which are more likely to be located in low-density regions of the host galaxy.

LARGE ANGULAR SCALE POLARIZATION OF THE COSMIC MICROWAVE BACKGROUND RADIATION AND THE FEASIBILITY OF ITS DETECTION

In addition to its spectrum and temperature anisotropy, the 2.7 K cosmic microwave background (CMB) is also expected to exhibit a low level of polarization. The spatial power spectrum of the polar- ization can provide details about the formation of structure in the universe as well as its ionization history. Here we calculate the magnitude of the CMB polarization in various cosmological scenarios, with both an analytic and a numerical method. We then outline the fundamental challenges to measur- ing these signals and focus on two of them: achieving adequate sensitivity and removing contamination due to foreground sources. We describe the design of a ground-based instrument (Polarization Obser- vations of Large Angular Regions) that could detect polarization of the CMB at large angular scales in the next few years. Subject headings: cosmic microwave background E cosmology: theory E polarization

A Limit on the Large Angular Scale Polarization of the Cosmic Microwave Background

We present an upper limit on the polarization of the cosmic microwave background (CMB) at 7 angular scales in the frequency band between 26 and 36 GHz, produced by the Polarization Observations of Large Angular Regions experiment. The campaign produced a map of linear polarization over the right ascension range 112–275 at declination 43. The model-independent upper limit on the E-mode polarization component of the CMB at angular scales is 10 mK (95% confidence). The corresponding limit for the B-mode is also 10 mK. l p 2–20 Constraining the B-mode power to be zero, the 95% confidence limit on E-mode power alone is 8 mK. Subject headings: cosmic microwave background — cosmology: observations — polarization

THE SPECTRUM OF INTEGRATED MILLIMETER FLUX OF THE MAGELLANIC CLOUDS AND 30 DORADUS FROM TOPHAT AND DIRBE DATA

We present measurements of the integrated flux relative to the local background of the Large and Small Magellanic Clouds and the region 30 Doradus (the Tarantula Nebula) in the LMC in four frequency bands centered at 245, 400, 460, and 630 GHz, based on observations made with the TopHat telescope. We combine these observations with the corresponding measurements for the DIRBE bands 8, 9, and 10 to cover the frequency range 245-3000 GHz (100-1220 μm) for these objects. We present spectra for all three objects and fit these spectra to a single-component graybody emission model and report best-fit dust temperatures, optical depths, and emissivity power-law indices, and we compare these results with other measurements in these regions and elsewhere. Using published dust grain opacities, we estimate the mass of the measured dust component in the three regions.

QUBIC: The QU Bolometric Interferometer For Cosmology

The primordial B-mode polarisation of the Cosmic Microwave Background is the imprints of the gravitational wave background generated by inflation. Observing the B-mode is up to now the most direct way to constrain the physics of the primordial Universe, especially inflation. To detect these B-modes, high sensitivity is required as well as an exquisite control of systematics effects. To comply with these requirements, we propose a new instrument called QUBIC (Q and U Bolometric Interferometer for Cosmology) based on bolometric interferometry. The control of systematics is obtained with a close-packed interferometer while bolometers cooled to very low temperature allow for high sensitivity. We present the architecture of this new instrument, the status of the project and the self-calibration technique which allows accurate measurement of the instrumental systematic effects.

Compass: An upper limit on cosmic microwave background polarization at an angular scale of 20'

COMPASS is an on-axis 2.6 meter telescope coupled to a correlation polarimeter operating at a wavelength of 1 cm. The entire instrument was built specifically for CMB polarization studies. We report here on observations of February 2001 - April 2001 using this system. We set an upper limit on E-mode polarized anisotropies of 33.5 uK (95% confidence limit) in the l-range 200-600.COMPASS is an on-axis 2.6 m telescope coupled to a correlation polarimeter operating at a wavelength of 1 cm. The entire instrument was built specifically for cosmic microwave background (CMB) polarization studies. We report here on observations of 2001 February-April using this system. We set an upper limit on E-mode polarized anisotropies of 1036 μK2 (95% confidence limit) in the l range 93-555.

An instrument for investigating the large angular scale polarization of the cosmic microwave background

We describe the design and performance of a microwave polarimeter used to make precision measurements of polarized astrophysical radiation in three microwave frequency bands spanning 26-36 GHz. The instrument uses cooled HEMT amplifiers in a correlation polarimeter configuration to achieve high sensitivity and long-term stability. The instrument demonstrates long-term stability and has produced the most restrictive upper limits to date on the large angular scale polarization of the 2.7 K cosmic microwave background radiation.

Measurements of anisotropy in the cosmic microwave background radiation at 0.5 deg angular scales near the star gamma ursae minoris

We present results from a four-frequency observation of a 6 deg x 0.6 deg strip of the sky centered near the star Gamma Ursae Minoris (GUM) during the fourth flight of the Millimeter-wave Anistropy experiment(MAX). The observation was made with a 1.4 deg peak-to-peak sinusoidal chop in all bands. The FWHM beam sizes were 0.55 deg +/- 0.05 deg at 3.5 per cm and 0.75 deg +/- 0.05 deg at 6, 9, and 14 per cm. During this observation significant correlated structure was observed at 3.5, 6 and 9 per cm with amplitudes similar to those observed in the GUM region during the second and third fligts of MAX. The frequency spectrum is consistent with cosmic microwave background (CMB) and inconsistent with thermal emission from interstellar dust. The extrapolated amplitudes of synchrotron and free-free emission are too small to account for the amplitude of the observed structure, If all of the structure is attributed to CMB anisotropy with a Gaussian autocorrelation function and a coherence angle of 25 min, then the most probable values of delta T/TCMB in the 3.5, 6 and 9 per cm bads are (4.3 +2.7/-1.6) x 10-5, 2.8 (+4.3/-1/1) x 10-5, and 3.5 (+3.0/-1.6) x 10-5 (95% confidence upper and lower limits), respectively.

Large-scale Polarization of the Microwave Background and Foreground

The DASI discovery of cosmic microwave background (CMB) polarization has opened a new chapter in cosmology. Most of the useful information about inflationary gravitational waves and reionization is on large angular scales where galactic foreground contamination is the worst, so a key challenge is to model, quantify, and remove polarized foregrounds. We use the POLAR experiment, COBE/DMR and radio surveys to provide the strongest limits to date on the TE cross-power spectrum of the CMB on large angular scales and to quantify the polarized synchrotron radiation, which is likely to be the most challenging polarized contaminant for the WMAP satellite. We find that the synchrotron E and B contributions are equal to within 10% from 408–820 MHz with a hint of E domination at higher frequencies. We quantify Faraday rotation and depolarization effects in the two-dimensional (l,ν) plane and show that they cause the synchrotron polarization percentage to drop both towards lower frequencies and towards lower multipoles.

Calibration of millimeter-wave polarimeters using a thin dielectric sheet

We present the theory and application of a novel calibration system for millimeter and microwave polarimeters. The technique is a simple extension of the conventional wire-grid approach, but employs a thin dielectric sheet rather than a grid. The primary advantage of this approach is to obtain a calibration signal that is only slightly polarized, which can be beneficial for certain applications such as astronomical radiometers that measure very low levels of polarization, or systems with a small dynamic range. We compare this approach with other calibration techniques and discuss its successful use in the calibration of the polarization observations of large angular regions experiment, designed to measure polarization in cosmic microwave background radiation.