Directionality in the Wilkinson Microwave Anisotropy Probe polarization data

Polarization is the next frontier of cosmic microwave background analysis, but its signal is dominated over much of the sky by foregrounds which must be carefully removed. To determine the efficacy of this cleaning, it is necessary to have sensitive tests for residual foreground contamination in polarization sky maps. The dominant Galactic foregrounds introduce a large-scale anisotropy on to the sky, so it makes sense to use a statistic sensitive to overall directionality for this purpose. Here, we adapt the rapidly computable     statistic of Bunn and Scott to polarization data, and demonstrate its utility as a foreground monitor by applying it to the low-resolution Wilkinson Microwave Anisotropy Probe 3-yr sky maps. With a thorough simulation of the maps' noise properties, we find no evidence for contamination in the foreground cleaned sky maps.     

Limits on the detectability of the CMB B-mode polarization imposed by foregrounds

We investigate which practical constraints are imposed by foregrounds on the detection of the B-mode polarization generated by gravitational waves, in the case of experiments of the type currently being planned. As the B-mode signal is probably dominated by foregrounds at all frequencies, the detection of the cosmological component depends drastically on our ability to remove foregrounds. We provide an analytical expression with which to estimate the level of the residual polarization for Galactic foregrounds, according to the method employed for their subtraction. We interpret this result in terms of the lower limit of the tensor-to-scalar ratio r that allows us to disentangle the cosmological B-mode polarization from the foreground contribution. Polarized emission from extragalactic radio sources and gravitational lensing is also taken into account. As a first approach, we consider the ideal limit of an instrumental noise-free experiment: for full-sky coverage and a resolution of 1°, we obtain a limit of   r ∼ 10⁻⁴  . This value can be improved by high-resolution experiments and, in principle, there is no clear fundamental limit on the detectability of the polarization of gravitational waves. Our analysis is also applied to planned or hypothetical future polarization experiments, taking into account expected noise levels.     

Galactic synchrotron emission according to the data of the RZF survey conducted at the RATAN-600 radio telescope

Deep 1–49 cm surveys of the circumzenithal sky area performed using the RATAN-600 radio telescope allowed the spectral index of Galactic synchrotron emission in the 7.6–49 cm wavelength interval to be refined. The data obtained are inconsistent with the model of synchrotron emission adopted to interpret the results of the first year of the WMAP mission, which led to the hypothesis of the early secondary ionization of the Universe at redshifts Z > 10–30. New observations made with the RATAN-600 demonstrated the possibility of deep studies of the intensity and polarization of the microwave background (the E component) in ground-based experiments at short centimeter wavelengths. Galactic synchrotron emission may as well limit the possibilities of space- and ground-based studies of the polarization of cosmic microwave background radiation arising as a result of scattering induced by relic gravitational waves (the B component). The sky area studied with the RATAN-600 is intended to be used to interpret the PLANCK mission data in order to ensure a more detailed account of the role of the Galactic synchrotron emission.     

The inverse problem for pulsating neutron stars: a 'fingerprint analysis' for the supranuclear equation of state

We study the problem of detecting, and inferring astrophysical information from, gravitational waves from a pulsating neutron star. We show that the fluid f and p modes, as well as the gravitational-wave w modes, may be detectable from sources in our own Galaxy, and investigate how accurately the frequencies and damping rates of these modes can be inferred from a noisy gravitational-wave data stream. Based on the conclusions of this discussion we propose a strategy for revealing the supranuclear equation of state using the neutron star fingerprints: the observed frequencies of an f and a p mode. We also discuss how well the source can be located in the sky using observations with several detectors.     

The Cosmic Foreground Explorer (COFE): A balloon-borne microwave polarimeter to characterize polarized foregrounds

The COsmic Foreground Explorer (COFE) is a balloon-borne microwave polarimeter designed to measure the low-frequency and low-ℓ characteristics of dominant diffuse polarized foregrounds. Short duration balloon flights from the Northern and Southern Hemispheres will allow the telescope to cover up to 80% of the sky with an expected sensitivity per pixel better than 100 μK/deg² from 10 GHz to 20 GHz. This is an important effort toward characterizing the polarized foregrounds for future CMB experiments, in particular the ones that aim to detect primordial gravity wave signatures in the CMB polarization angular power spectrum.     

Maximizing the probability of detecting an electromagnetic counterpart of gravitational-wave events

Compact binary coalescences are a promising source of gravitational waves for second-generation interferometric gravitational-wave detectors such as advanced LIGO and advanced Virgo. These are among the most promising sources for joint detection of electromagnetic (EM) and gravitational-wave (GW) emission. To maximize the science performed with these objects, it is essential to undertake a followup observing strategy that maximizes the likelihood of detecting the EM counterpart. We present a follow-up strategy that maximizes the counterpart detection probability, given a fixed investment of telescope time. We show how the prior assumption on the luminosity function of the electro-magnetic counterpart impacts the optimized followup strategy. Our results suggest that if the goal is to detect an EM counterpart from among a succession of GW triggers, the optimal strategy is to perform long integrations in the highest likelihood regions. For certain assumptions about source luminosity and mass distributions, we find that an optimal time investment that is proportional to the 2/3 power of the surface density of the GW location probability on the sky. In the future, this analysis framework will benefit significantly from the 3-dimensional localization probability.     

Lensed CMB temperature and polarization maps from the Millennium Simulation

We have constructed the first all-sky cosmic microwave background (CMB) temperature and polarization lensed maps based on a high-resolution cosmological N -body simulation, the Millennium Simulation (MS). We have exploited the lensing potential map obtained using a previously developed map-making procedure which integrates along the line-of-sight the MS dark matter distribution by stacking and randomizing the simulation boxes up to   z = 127  , and which semi-analytically supplies the large-scale power in the angular lensing potential that is not correctly sampled by the N -body simulation. The lensed sky has been obtained by properly modifying the latest version of the LensPix code to account for the MS structures. We have also produced all-sky lensed maps of the so-called  ψ _E   and  ψ _B   potentials, which are directly related to the electric and magnetic types of polarization. The angular power spectra of the simulated lensed temperature and polarization maps agree well with semi-analytic estimates up to   l ≤ 2500  , while on smaller scales we find a slight excess of power which we interpret as being due to non-linear clustering in the MS. We also observe how non-linear lensing power in the polarized CMB is transferred to large angular scales by suitably misaligned modes in the CMB and the lensing potential. This work is relevant in view of the future CMB probes, as a way to analyse the lensed sky and disentangle the contribution from primordial gravitational waves.     

Small-scale cosmic microwave background polarization from reionization

We discuss fluctuations in the cosmic microwave background (CMB) polarization due to scattering from reionized gas at low redshifts. Polarization is produced by re-scattering of the primordial temperature anisotropy quadrupole and of the kinematic quadrupole that arises from gas motion transverse to the line of sight. We show that both effects produce equal E- and B-parity polarization, and are, in general, several orders of magnitude below the dominant polarization contributions at the last scattering surface to E-modes or the gravitational-lensing contribution to B-modes at intermediate redshifts. These effects are also several orders of magnitude below the B polarization due to lensing even after subtraction with higher-order correlations, and are thus too small to constitute a background for searches for the polarization signature of inflationary gravitational waves.     

Fluctations in the cosmic microwave background arising from low-frequency gravitational radiation

Intense low-frequency intergalactic gravitational radiation with wave lengths λ smaller than the HUBBLE distance λ_H ≌ 3000 (100/H₀) Mpc but not exceedingly small compared to λ_H. generates anisotropies in the microwave background radiation. One contribution results from the local wave field and produces mainly a quadrupole-type temperature variation on the sky. Available data on large-scale microwave fluctuations do not exclude appreciable amounts of gravitational background radiation in the Megaparsec wave band. A more sensitive test is provided by a second far-field contribution, which has a small angular scale. Its amplitude depends strongly on the ratio of the (present) rest mass density to the HUBBLE constant, if a cosmological origin of the blackbody radiation is assumed. In a low-density universe, pre-galactic COMPTON scattering of the blackbody radiation is not able to reduce the fluctuations caused by the low-frequency gravitational wave field. The recent small-scale data by PARIJSKIJ would allow only small amplitudes of gravitational waves with an energy density significantly below the critical cosmological density. On the other hand, in a high-density universe, the small angular scale fluctuation in the blackbody radiation is completely damped out, and a gravitational radiation cosmos reaching the critical density is admitted. Independent of the matter density, the data by PARIJSKIJ would confine gravitational background radiation to insignificant amplitudes if a discrete source model for the origin of the microwave background has to be assumed.     

Non-random phases in non-trivial topologies

We present a new technique for constraining the topology of the Universe. The method exploits the existence of correlations in the phases of the spherical harmonic coefficients of the cosmic microwave background (CMB) temperature pattern associated with matched pairs of circles seen in the sky in universes with non-trivial topology. The method is computationally faster than all other statistics developed to hunt for these matched circles. We applied the method to a range of simulations with topologies of various forms and on different scales. A characteristic form of phase correlation is found in the simulations. We also applied the method to preliminary CMB maps derived from WMAP , but the separation of topological effects from e.g. foregrounds is not straightforward.     

Using HI to probe large scale structures at z∼3

The redshifted 1420 MHz emission from the HI in unresolved damped Lyman-α clouds at high z will appear as a background radiation in low frequency radio observations. This holds the possibility of a new tool for studying the universe at high-z, using the mean brightness temperature to probe the HI content and its fluctuations to probe power spectrum. Existing estimates of the HI density atz−3 imply a mean brightness temperature of 1 mK at 320 MHz. The cross-correlation between the temperature fluctuation across different frequencies and sight lines is predicted to vary from 10⁻⁷ K² to 10⁻⁸ K² over intervals corresponding to spatial scales from 10 Mpc to 40 Mpc for some of the currently favoured cosmological models. Comparing this with the expected sensitivity of the GMRT, we find that this can be detected with ∼ 10 hrs of integration, provided we can distinguish it from the galactic and extragalactic foregrounds which will swamp this signal. We discuss a strategy based on the very distinct spectral properties of the foregrounds as against the HI emission, possibly allowing the removal of the foregrounds from the observed maps.     

Foreground removal from CMB temperature maps using an MLP neural network

One of the main obstacles for extracting the Cosmic Microwave Background (CMB) signal from observations in the mm-submm range is the foreground contamination by emission from Galactic components: mainly synchrotron, free-free and thermal dust emission. Due to the statistical nature of the intrinsic CMB signal it is essential to minimize the systematic errors in the CMB temperature determinations. Following the available knowledge of the spectral behavior of the Galactic foregrounds simple power law-like spectra have been assumed. The feasibility of using a simple neural network for extracting the CMB temperature signal from the combined signal CMB and the foregrounds has been investigated. As a specific example, we have analysed simulated data, as expected from the ESA Planck CMB mission. A simple multilayer perceptron neural network with 2 hidden layers can provide temperature estimates over more than 80 per cent of the sky that are to a high degree uncorrelated with the foreground signals. A single network will be able to cover the dynamic range of the Planck noise level over the entire sky.     

The Sunyaev–Zel'dovich effect and Faraday rotation contributions of galaxy groups to the CMB angular power spectrum

The Sunyaev–Zel'dovich (SZ) effect and the Faraday rotation from haloes are examined over a wide mass range, including gas condensation and magnetic field evolution. Contributions to the cosmic microwave background (CMB) angular power spectrum are evaluated for galaxy clusters, galaxy groups and galaxies. Smaller mass haloes are found to play a more important role than massive haloes for the B -mode polarization associated with the SZ CMB anisotropies. The B modes from the Faraday rotation dominate the secondary B modes caused by gravitational lensing at  ℓ > 3000  . Measurement of B -mode polarization in combination with the SZ power spectrum can potentially provide important constraints on intracluster magnetic field and gas evolution at early epochs.     

Optimizing Pulsar Searches Against Propagation Effects

Propagation effects are well known to limit the sensitivity of pulsar searches based on periodicity detections. I define several regimes for pulsar searches that are based on whether the search sensitivity is luminosity limited, dispersion limited or scattering limited. Consideration of these regimes allows general statements to be made about pulsar searches in and out of the Galactic plane. Telescope size matters, but only to a point. Once scattering becomes important it is better to search more sky (in a blind survey) than to integrate longer on a given sky position. Example surveys are described. This revised version was published online in July 2006 with corrections to the Cover Date.     

Univiewer utility for fast interactive 3D visualization of CMB maps in HEALPix pixelizaton

We describe the Univiewer utility for visualizing the celestialmaps in the HEALPix pixelization scheme, which is widely used in data reduction for various experiments involving observations of the cosmic microwave background radiation (CMB). The utility can be used to view the FITS files containing one or several extensions containing HEALPix maps of temperature, intensities, Stokes parameters, integration time per pixel values, etc. The user can interactively change the visualization parameters, apply a coordinate grid, project sky areas onto a plane for further detailed analyses, and compute power spectra. The utility uses OpenGL and wxWidgets cross-platform libraries.     

Determination of a temporally and spatially resolved supernova rate from OB stars within 5 kpc

We spatially and temporally resolve the future Supernova (SN) rate in the Solar vicinity and the whole Galaxy by comparing observational parameters of massive stars with theoretical models for estimating age and mass and, hence, the remaining lifetime until the SN explosion. Our SN rate derived in time and space for the future (few Myr) should be the same as in the last few Myr by assuming a constant rate. From BVRIJHK photometry, parallax, spectral type, and luminosity class we compile a Hertzsprung‐Russell diagram (HRD) for 25027 massive stars and derive extinction, and luminosity, then mass, age, and remaining lifetime from evolutionary models. Within 600 pc our sample of SN progenitors and, hence, SN prediction, is complete, and all future SN events of our sample stars take place in 8 % of the area of the sky, whereas 90 % of the events take place in 7 % of the area of the sky. The current SN rate within 600 pc is increased by a factor of 5–6 compared with the Galactic rate. For a distance of 5 kpc our sample is incomplete, nevertheless 90 % of those SN events take place in only 12 % of the area of the projected sky. If the SN rate in the near future is the same as the recent past, there should be unknown young neutron stars concentrated in those areas. Our distribution can be used as input for constraints of gravitational waves detection and for neutron star searches. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Strong-field tests of gravity using pulsars and black holes

The sensitivity of the SKA enables a number of tests of theories of gravity. A Galactic Census of pulsars will discover most of the active pulsars in the Galaxy beamed toward us. In this census will almost certainly be pulsar–black hole binaries as well as pulsars orbiting the super-massive black hole in the Galactic centre. These systems are unique in their capability to probe the ultra-strong field limit of relativistic gravity. These measurements can be used to test the Cosmic Censorship Conjecture and the No-Hair theorem.The large number of millisecond pulsars discovered with the SKA will also provide a dense array of precision clocks on the sky. These clocks will act as the multiple arms of a huge gravitational wave detector, which can be used to detect and measure the stochastic cosmological gravitational wave background that is expected from a number of sources.     

A metric and optimization scheme for microlens planet searches

OGLE III and MOA-II are discovering 600–1000 Galactic bulge microlens events each year. This stretches the resources available for intensive follow-up monitoring of the light curves in search of anomalies caused by planets near the lens stars. We advocate optimizing microlens planet searches by using an automatic prioritization algorithm based on the planet detection zone area probed by each new data point. This optimization scheme takes account of the telescope and detector characteristics, observing overheads, sky conditions and the time available for observing on each night. The predicted brightness and magnification of each microlens target are estimated by fitting to available data points. The optimization scheme then yields a decision on which targets to observe and which to skip, and a recommended exposure time for each target, designed to maximize the planet detection capability of the observations. The optimal strategy maximizes detection of planet anomalies, and this must be coupled with rapid data reduction to trigger continuous follow-up of anomalies that are thereby found. A web interface makes the scheme available for use by human or robotic observers at any telescope. We also outline a possible self-organizing scheme that may be suitable for coordination of microlens observations by a heterogeneous telescope network.