Results for "A. J. Banday"

total 339012took 0.18s
Constraints on the topology of the Universe derived from the 7-year WMAP dataDec 16 2010Feb 16 2011We impose constraints on the topology of the Universe determined from a search for matched circles in the temperature anisotropy patterns of the 7-year WMAP data. We pay special attention to the sensitivity of the method to residual foreground contamination ... More
Limits to Global Rotation and Shear From the COBE DMR 4-Year Sky MapsJan 15 1997Small departures from a homogeneous isotropic spacetime create observable features in the large-scale anisotropy of the cosmic microwave background. We cross-correlate the maps of the cosmic microwave background anisotropy from the Cosmic Background Explorer ... More
COBE Constraints on a Local group X-ray HaloSep 03 1996We investigate the effect of a putative X-ray emitting halo surrounding the Local Group of galaxies, and specifically the possible temperature anisotropies induced in the COBE-DMR four-year sky maps by an associated Sunyaev-Zel'dovich effect. By fitting ... More
A Scaling Index Analysis of the WMAP three year data: Signatures of non-Gaussianities and Asymmetries in the CMBFeb 06 2007Local scaling properties of the co-added foreground-cleaned three-year Wilkinson Microwave Anisotropy Probe (WMAP) data are estimated using weighted scaling indices. The scaling index method (SIM) is - for the first time - adapted and applied to the case ... More
Foreground analysis of the WMAP three-year data with FASTICAJul 11 2008We present an analysis of the foreground emission present in the WMAP 3-year data as determined by the method of Independent Component Analysis. We derived coupling coefficients between the WMAP data and foreground templates which are then used to infer ... More
New insights into foreground analysis of the WMAP five-year data using FASTICAOct 23 2009Oct 27 2009In this paper, we present a foreground analysis of the WMAP 5-year data using the FASTICA algorithm, improving on the treatment of the WMAP 3-year data in Bottino et al 2008. We revisit the nature of the free-free spectrum with the emphasis on attempting ... More
COBE-DMR-normalisation for inflationary flat dark matter modelsJun 14 1995The two-year COBE-DMR 53 and 90 GHz sky maps, in both galactic and ecliptic coordinates, are used to determine the normalisation of inflationary universe models with a flat global geometry and adiabatic density perturbations. The appropriately normalised ... More
Lyman-alpha forest-CMB cross-correlation and the search for the ionized baryons at high redshiftDec 14 2005The intergalactic neutral hydrogen which is responsible for the Lyman alpha forest of quasar absorption is a tracer of much larger amounts of ionised hydrogen. The ionised component has yet to be detected directly, but is expected to scatter CMB photons ... More
Testing the cosmological principle of isotropy: local power spectrum estimates of the WMAP dataApr 09 2004We apply the Gabor transform methodology proposed in (Hansen et al. 2002, 2003) to the WMAP data in order to test the statistical properties of the CMB fluctuation field and specifically to evaluate the fundamental assumption of cosmological isotropy. ... More
Flat Dark Matter Dominated Models with Hybrid Adiabatic Plus Isocurvature Initial ConditionsNov 19 1995Nov 24 1995We investigate the consequences of flat, dark-matter dominated cosmogonies with hybrid isocurvature and adiabatic initial perturbations and with Harrison-Zel'dovich primordial spectrum normalised to the $COBE$-DMR two-year measurements. We show that whilst ... More
Constraints on the topology of the Universe derived from the 7-year WMAP CMB data and prospects of constraining the topology using CMB polarisation mapsMar 16 2013We impose constraints on the topology of the Universe determined from a search for matched circles in the cosmic microwave background (CMB) temperature anisotropy patterns of the 7-year WMAP data. We pay special attention to the sensitivity of the method ... More
Non-Gaussian Signatures in the five-year WMAP data as identified with isotropic scaling indicesMay 18 2009Jul 21 2009We continue the analysis of non-Gaussianities in the CMB by means of the scaling index method (SIM, Raeth, Schuecker & Banday 2007) by applying this method on the 5-year WMAP data. We compare each of the results with 1000 Monte Carlo simulations mimicing ... More
The Hot and Cold Spots in Five-Year WMAP DataMar 25 2009We present an extensive frequentist analysis of the one-point statistics (number, mean, variance, skewness and kurtosis) and two-point correlation functions determined for the local extrema of the cosmic microwave background temperature field observed ... More
Constraining the topology of the Universe using the polarised CMB mapsNov 25 2011Feb 22 2012We study the possibility for constraining the topology of the Universe by means of the matched circles statistic applied to polarised cosmic microwave background (CMB) anisotropy maps. The advantages of using the CMB polarisation maps in studies of the ... More
Collected Contributions from the COBE-DMR Group to the Maryland Astrophysics Meeting on Dark MatterFeb 06 1995The three papers summarize the methods employed by the COBE-DMR group to analyze the power spectrum of the two-year DMR anisotropy maps. Results for the slope and normalization of the power spectrum are presented and compared. The implications of these ... More
Low-order multipole maps of CMB anisotropy derived from WMAPMay 02 2004Dec 13 2004Recent analyses of the WMAP data have suggested that the low-order multipoles of the CMB anisotropy distribution show cosmologically interesting and unexpected morphologies and amplitudes. In this paper, we apply a power equalization (PE) filter to the ... More
The N-point correlation functions of the COBE-DMR maps revisitedJun 19 2002Sep 03 2002We calculate the two-, three- and (for the first time) four-point correlation functions of the COBE-DMR 4-year sky maps, and search for evidence of non-Gaussianity by comparing the data to Monte Carlo-simulations of the functions. The analysis is performed ... More
On the Non-Gaussianity Observed in the COBE-DMR Sky MapsAug 06 1999Oct 25 1999In this paper we pursue the origin of the non-Gaussianity determined by a bispectrum analysis of the COBE-DMR 4-year sky maps. The robustness of the statistic is demonstrated by the rebinning of the data into 12 coordinate systems. By computing the bispectrum ... More
A search for concentric rings with unusual variance in the 7-year WMAP temperature maps using a fast convolution approachJul 30 2012Dec 14 2012We present a method for the computation of the variance of cosmic microwave background (CMB) temperature maps on azimuthally symmetric patches using a fast convolution approach. As an example of the application of the method, we show results for the search ... More
Towards a model of full-sky Galactic synchrotron intensity and linear polarisation: a re-analysis of the Parkes dataFeb 28 2002We have analysed the angular power spectra of the Parkes radio continuum and polarisation survey of the Southern galactic plane at 2.4 GHz. We have found that in the multipole range l=40-250 the angular power spectrum of the polarised intensity is well ... More
Connecting Synchrotron, Cosmic Rays, and Magnetic Fields in the Plane of the GalaxyMay 30 2011Feb 13 2018We extend previous work modeling the Galactic magnetic field in the plane using synchrotron emission in total and polarised intensity. In this work, we include a more realistic treatment of the cosmic-ray electrons using the GALPROP propagation code optimized ... More
Connecting Synchrotron, Cosmic Rays, and Magnetic Fields in the Plane of the GalaxyMay 30 2011We extend previous work modeling the Galactic magnetic field in the plane using synchrotron emission in total and polarised intensity. In this work, we include a more realistic treatment of the cosmic-ray electrons using the GALPROP propagation code optimized ... More
Topology of the universe from COBE-DMR; a wavelet approachMay 10 2002In this paper we pursue a new technique to search for evidence of a finite Universe, making use of a spherical mexican-hat wavelet decomposition of the microwave background fluctuations. Using the information provided by the wavelet coefficients at several ... More
An improved source-subtracted and destriped 408 MHz all-sky mapOct 17 2014Jun 10 2015The all-sky 408 MHz map of Haslam et al. is one the most important total-power radio surveys. It has been widely used to study diffuse synchrotron radiation from our Galaxy and as a template to remove foregrounds in cosmic microwave background data. However, ... More
Reappraising foreground contamination in the COBE-DMR dataFeb 10 2003Jul 14 2003With the advent of all-sky H-Alpha surveys it is possible to determine a reliable free-free template of the diffuse interstellar medium (Dickinson, Davies & Davis 2003) which can be used in conjunction with the synchrotron and dust templates to correct ... More
Cosmological parameters and the WMAP data revisitedJun 09 2004Several recent papers have made claims about the detection of an asymmetric distribution of large scale power in the cosmic microwave background anisotropy as measured by the WMAP satellite. In this paper, we investigate how the estimates of particular ... More
High-Latitude Galactic Emission in the COBE DMR Two-Year Sky MapsSep 29 1995We cross-correlate the COBE-DMR 2-year sky maps with spatial templates from long-wavelength radio surveys and the far-infrared COBE DIRBE maps. We place an upper limit on the spectral index of synchrotron radiation beta_{synch} < -2.9 between 408 MHz ... More
Three-Point Correlations in the COBE-DMR Two-Year Anisotropy MapsMar 07 1995We compute the three-point temperature correlation function of the COBE Differential Microwave Radiometer (DMR) two-year sky maps to search for evidence of non-Gaussian temperature fluctuations. We detect three-point correlations in our sky with a substantially ... More
Non-cosmological Signal Contributions to the COBE-DMR Four-Year Sky MapsJan 12 1996We limit the possible contributions from non-cosmological sources to the COBE-DMR four-year sky maps. The DMR data are cross-correlated with maps of rich clusters, extragalactic IRAS sources, HEAO-1 A-2 X-ray emission and 5 GHz radio sources using a Fourier ... More
Gaussian Statistics of the Cosmic Microwave Background: Correlation of Temperature Extrema In the COBE DMR Two-Year Sky MapsAug 19 1994We use the two-point correlation function of the extrema points (peaks and valleys) in the COBE Differential Microwave Radiometers (DMR) 2-year sky maps as a test for non-Gaussian temperature distribution in the cosmic microwave background anisotropy. ... More
Probing non-Gaussianities on Large Scales in WMAP5 and WMAP7 Data using SurrogatesMay 14 2010Probing Gaussianity represents one of the key questions in modern cosmology, because it allows to discriminate between different models of inflation. We test for large-scale non-Gaussianities in the cosmic microwave background (CMB) in a model-independent ... More
Astro-ph communication: Simulations of the WMAP Internal Linear Combination sky mapAug 08 2005Following this astro-ph communication, we release a set of 10,000 WMAP ILC simulations, produced as described by Eriksen et al. (2004). We strongly encourage that an analysis of these simulations accompanies any scientific analysis of the observed ILC ... More
On Foreground Removal from the Wilkinson Microwave Anisotropy Probe Data by an Internal Linear Combination Method: Limitations and ImplicationsMar 03 2004Aug 23 2004We study the Internal Linear Combination (ILC) method presented by the Wilkinson Microwave Anisotropy Probe (WMAP) science team, with the goal of determining whether it may be used for cosmological purposes, as a template-free alternative to existing ... More
Asymmetries in the CMB anisotropy fieldJul 30 2003Feb 26 2004We report on the results from two independent but complementary statistical analyses of the WMAP first-year data, based on the power spectrum and N-point correlation functions. We focus on large and intermediate scales (larger than about 3 degrees) and ... More
Testing for Non-Gaussianity in the Wilkinson Microwave Anisotropy Probe Data: Minkowski Functionals and the Length of the SkeletonJan 14 2004Aug 23 2004The three Minkowski functionals and the recently defined length of the skeleton are estimated for the co-added first-year Wilkinson Microwave Anisotropy Probe (WMAP) data and compared with 5000 Monte Carlo simulations, based on Gaussian fluctuations with ... More
Search for non-Gaussianities in the WMAP data with the Scaling Index MethodAug 02 2011In the recent years, non-Gaussianity and statistical isotropy of the Cosmic Microwave Background (CMB) was investigated with various statistical measures, first and foremost by means of the measurements of the WMAP satellite. In this Review, we focus ... More
The primordial non-Gaussianity of local type (f_NL) in the WMAP 5-year data: the length distribution of CMB skeletonMay 31 2010Jun 01 2010We present skeleton studies of non-Gaussianity in the CMB temperature anisotropy observed in the WMAP5 data. The local skeleton is traced on the 2D sphere by cubic spline interpolation which leads to more accurate estimation of the intersection positions ... More
The two-and three-point correlation functions of the polarized five-year WMAP sky mapsOct 30 2009Jan 23 2010We present the two- and three-point real space correlation functions of the five-year WMAP sky maps, and compare the observed functions to simulated LCDM concordance model ensembles. In agreement with previously published results, we find that the temperature ... More
Evidence of vorticity and shear at large angular scales in the WMAP data: a violation of cosmological isotropy?Mar 09 2005Sep 02 2005Motivated by the large-scale asymmetry observed in the cosmic microwave background sky, we consider a specific class of anisotropic cosmological models -- Bianchi type VII_h -- and compare them to the WMAP first-year data on large angular scales. Remarkably, ... More
The N-point correlation functions of the first-year Wilkinson Microwave Anisotropy Probe sky mapsJul 13 2004Dec 07 2004We compute the two-, three- and four-point correlation functions from the Wilkinson Microwave Anisotropy Probe (WMAP) first-year data, and compare these to a Monte Carlo ensemble of 5000 realizations, based on the best-fit WMAP running-index spectrum ... More
Hemispherical power asymmetry in the three-year Wilkinson Microwave Anisotropy Probe sky mapsJan 04 2007May 29 2007We consider the issue of hemispherical power asymmetry in the three-year WMAP data, adopting a previously introduced modulation framework. Computing both frequentist probabilities and Bayesian evidences, we find that the model consisiting of an isotropic ... More
Bianchi Type VII_h Models and the WMAP 3-year DataJun 02 2006Context. A specific example of Bianchi Type VIIh models, i.e. those including universal rotation (vorticity) and differential expansion (shear), has been shown in Jaffe et al. (2005) to correlate unexpectedly with the WMAP first-year data. Aims. We re-assess ... More
On the Viability of Bianchi Type VIIh Models with Dark EnergyDec 16 2005We generalize the predictions for the CMB anisotropy patterns arising in Bianchi type VIIh universes to include a dark energy component. We consider these models in light of the result of Jaffe et al. (2005a,b) in which a correlation was found on large ... More
Correlating Fourier phase information with real-space higher order statisticsNov 20 2013We establish for the first time heuristic correlations between harmonic space phase information and higher order statistics. Using the spherical full-sky maps of the cosmic microwave background as an example we demonstrate that known phase correlations ... More
Power Asymmetry in Cosmic Microwave Background Fluctuations from Full Sky to Sub-degree Scales: Is the Universe Isotropic?Dec 19 2008We repeat and extend the analysis of Eriksen et al 2004 and Hansen et al 2004 testing the isotropy of the Cosmic Microwave Background (CMB) fluctuations. We find that the hemispherical power asymmetry previously reported for the largest scales l=2-40 ... More
Foreground Analysis Using Cross-Correlations of External Templates on the 7-year WMAP dataDec 02 2011WMAP data when combined with ancillary data on free-free, synchrotron and dust allow an improved understanding of the spectrum of emission from each of these components. Here we examine the sky variation at intermediate and high latitudes using a cross-correlation ... More
Directional dependence of LCDM cosmological parametersMar 21 2013Jul 26 2013We study hemispherical power asymmetry (Eriksen et. al. 2004, Hansen et. al. 2004, Hansen et. al. 2009) in the WMAP 9-year data. We analyse the combined V- and W-band sky maps, after application of the KQ85 mask, and find that the asymmetry is statistically ... More
Probing non-Gaussianities in the CMB on an incomplete sky using surrogatesJul 13 2012We demonstrate the feasibility to generate surrogates by Fourier-based methods for an incomplete data set. This is performed for the case of a CMB analysis, where astrophysical foreground emission, mainly present in the Galactic plane, is a major challenge. ... More
Frequentist comparison of CMB local extrema statistics in the five-year WMAP data with two anisotropic cosmological modelsOct 19 2009We present local extrema studies of two models that introduce a preferred direction into the observed cosmic microwave background (CMB) temperature field. In particular, we make a frequentist comparison of the one- and two-point statistics for the dipole ... More
Foreground Subtraction of Cosmic Microwave Background Maps using WI-FIT (Wavelet based hIgh resolution Fitting of Internal Templates)Mar 13 2006We present a new approach to foreground removal for Cosmic Microwave Background (CMB) maps. Rather than relying on prior knowledge about the foreground components, we first extract the necessary information about them directly from the microwave sky maps ... More
Multipole vector anomalies in the first-year WMAP data: a cut-sky analysisJul 08 2005Aug 15 2005We apply the recently defined multipole vector framework to the frequency-specific first-year WMAP sky maps, estimating the low-l multipole coefficients from the high-latitude sky by means of a power equalization filter. While most previous analyses of ... More
COBE-DMR constraints on the nonlinear coupling parameter: a wavelet based methodNov 18 2002Nonlinearity introduced in slow-roll inflation will produce weakly non-Gaussian CMB temperature fluctuations. We have simulated non-Gaussian large scale CMB maps (including COBE-DMR constraints) introducing an additional quadratic term in the gravitational ... More
A model-independent test for scale-dependent non-Gaussianities in the CMBOct 21 2008Mar 18 2009We present a model-independent method to test for scale-dependent non-Gaussianities in combination with scaling indices as test statistics. Therefore, surrogate data sets are generated, in which the power spectrum of the original data is preserved, while ... More
Fast and Efficient Template Fitting of Deterministic Anisotropic Cosmological Models Applied to WMAP DataMar 31 2006We explore methods of fitting templates to cosmic microwave background (CMB) data, and in particular demonstrate the application of the total convolver algorithm as a fast method of performing a search over all possible locations and orientations of the ... More
Astrophysical components separation of COBE-DMR 4yr data with FastICAMar 31 2003We present an application of the fast Independent Component Analysis method to the COBE-DMR 4yr data. Although the signal-to-noise ratio in the COBE-DMR data is typically $\sim 1$, the approach is able to extract the CMB signal with high confidence when ... More
The Trispectrum of the 4 Year COBE-DMR dataNov 13 2001Feb 04 2002We propose an estimator for the trispectrum of a scalar random field on a sphere, discuss its geometrical and statistical properties, and outline its implementation. By estimating the trispectrum of the 4 year COBE-DMR data (in HEALPix pixelization) we ... More
The scalar perturbation spectral index n_s: WMAP sensitivity to unresolved point sourcesOct 10 2007Precision measurement of the scalar perturbation spectral index, n_s, from the Wilkinson Microwave Anisotropy Probe temperature angular power spectrum requires the subtraction of unresolved point source power. Here we reconsider this issue. First, we ... More
CMB signal in WMAP 3yr data with FastICASep 08 2006We present an application of the fast Independent Component Analysis (FastICA) to the WMAP 3yr data with the goal of extracting the CMB signal. We evaluate the confidence of our results by means of Monte Carlo simulations including CMB, foreground contaminations ... More
Estimating N-Point Correlation Functions from Pixelized Sky MapsOct 29 2003Jan 23 2004We develop, implement and test a set of algorithms for estimating N-point correlation functions from pixelized sky maps. These algorithms are slow, in the sense that they do not break the O(N_pix^N) barrier, and yet, they are fast enough for efficient ... More
COBE-DMR-Normalized Open CDM CosmogoniesAug 10 1996Cut-sky orthogonal mode analyses of the COBE-DMR 53 and 90 GHz sky maps are used to determine the normalization of a variety of open cosmogonical models based on the cold dark matter scenario. To constrain the allowed cosmological-parameter range for ... More
The Dipole Observed in the COBE DMR Four-Year DataJan 26 1996Sep 04 1996The largest anisotropy in the cosmic microwave background (CMB) is the $\approx 3$ mK dipole assumed to be due to our velocity with respect to the CMB. Using the four year data set from all six channels of the COBE Differential Microwave Radiometers (DMR), ... More
The angular power spectrum of radio emission at 2.3 GHzMar 15 2001We have analysed the Rhodes/HartRAO survey at 2326 MHz and derived the global angular power spectrum of Galactic continuum emission. In order to measure the angular power spectrum of the diffuse component, point sources were removed from the map by median ... More
Modelling the Galactic Magnetic Field on the Plane in 2DJul 23 2009Jan 29 2010We present a method for parametric modelling of the physical components of the Galaxy's magnetised interstellar medium, simulating the observables, and mapping out the likelihood space using a Markov Chain Monte-Carlo analysis. We then demonstrate it ... More
Scale-dependent non-Gaussianities in the WMAP data as identified by using surrogates and scaling indicesDec 14 2010Apr 27 2011We present a model-independent investigation of the WMAP data with respect to scale- dependent non-Gaussianities (NGs) by employing the method of constrained randomization. For generating so-called surrogate maps a shuffling scheme is applied to the Fourier ... More
Analysis of CMB foregrounds using a database for PlanckNov 03 2000Within the scope of the Planck IDIS (Integrated Data Information System) project we have started to develop the data model for time-ordered data and full-sky maps. The data model is part of the Data Management Component (DMC), a software system designed ... More
Tests for Non-Gaussian Statistics in the DMR Four-Year Sky MapsJan 12 1996We search the high-latitude portion of the COBE Differential Microwave Radiometers (DMR) 4-year sky maps for evidence of a non-Gaussian temperature distribution in the cosmic microwave background. The genus, 3-point correlation function, and 2-point correlation ... More
Search For Unresolved Sources In The COBE-DMR Two-Year Sky MapsFeb 02 1994We have searched the temperature maps from the COBE Differential Microwave Radiometers (DMR) first two years of data for evidence of unresolved sources. The high-latitude sky (|b| > 30\deg) contains no sources brighter than 192 uK thermodynamic temperature ... More
Template fitting of WMAP 7-year data: anomalous dust or flattening synchrotron emission?Dec 02 2011May 22 2012Anomalous microwave emission at 20-40 GHz has been detected across our Galactic sky. It is highly correlated with thermal dust emission and hence it is thought to be due to spinning dust grains. Alternatively, this emission could be due to synchrotron ... More
Increasing evidence for hemispherical power asymmetry in the five-year WMAP dataMar 06 2009Apr 20 2009(Abridged)Motivated by the recent results of Hansen et al. (2008) concerning a noticeable hemispherical power asymmetry in the WMAP data on small angular scales, we revisit the dipole modulated signal model introduced by Gordon et al. (2005). This model ... More
Power asymmetry in WMAP and Planck temperature sky maps as measured by a local variance estimatorFeb 04 2014Mar 24 2014We revisit the question of hemispherical power asymmetry in the WMAP and Planck temperature sky maps by measuring the local variance over the sky and on disks of various sizes. For the 2013 Planck sky map we find that none of the 1000 available isotropic ... More
Statistics and Topology of the COBE DMR First Year MapsDec 14 1993We use statistical and topological quantities to test the COBE-DMR first year sky maps against the hypothesis that the observed temperature fluctuations reflect Gaussian initial density perturbations with random phases. Recent papers discuss specific ... More
Template fitting of WMAP 7-year data: anomalous dust or flattening synchrotron emission?Dec 02 2011Feb 08 2018Anomalous microwave emission at 20-40 GHz has been detected across our Galactic sky. It is highly correlated with thermal dust emission and hence it is thought to be due to spinning dust grains. Alternatively, this emission could be due to synchrotron ... More
A determination of the Spectra of Galactic components observed by WMAPNov 14 2005Apr 07 2006WMAP data when combined with ancillary data on free-free, synchrotron and dust allow an improved understanding of the spectrum of emission from each of these components. Here we examine the sky variation at intermediate latitudes using a cross-correlation ... More
Looking for non-Gaussianity in the COBE-DMR data with spherical waveletsApr 23 2000We present an analysis of the Gaussianity of the 4-year COBE-DMR data (in HEALPix pixelisation) based on spherical wavelets. The skewness, kurtosis and scale-scale correlation spectra are computed from the detail wavelet coefficients at each scale. The ... More
Testing the Gaussianity of the COBE-DMR data with spherical waveletsApr 14 2000We investigate the Gaussianity of the 4-year COBE-DMR data (in HEALPix pixelisation) using an analysis based on spherical Haar wavelets. We use all the pixels lying outside the Galactic cut and compute the skewness, kurtosis and scale-scale correlation ... More
RMS Anisotropy in the COBE-DMR Four-Year Sky MapsJan 12 1996The sky-RMS is the simplest model-independent characterization of a cosmological anisotropy signal. The RMS temperature fluctuations determined from the $COBE$-DMR four-year sky maps are frequency independent, consistent with the hypothesis that they ... More
Microwave Emission at High Galactic LatitudesJan 12 1996We use the COBE Differential Microwave Radiometers (DMR) 4-year sky maps to model Galactic microwave emission at high latitudes (|b| > 20 deg). Cross-correlation of the DMR maps with Galactic template maps detects fluctuations in the high-latitude microwave ... More
Joint Bayesian component separation and CMB power spectrum estimationSep 07 2007Nov 05 2007We describe and implement an exact, flexible, and computationally efficient algorithm for joint component separation and CMB power spectrum estimation, building on a Gibbs sampling framework. Two essential new features are 1) conditional sampling of foreground ... More
No Higher Criticism of the Bianchi Corrected WMAP DataFeb 01 2006Motivated by the success of the Bianchi VII_h model in addressing many of the anomalies observed in the WMAP data (Jaffe et al.), we present calculations in real and in wavelet space of the Higher Criticism statistic of the Bianchi corrected Wilkinson ... More
Foreground separation using a flexible maximum-entropy algorithm: an application to COBE dataFeb 05 2003Apr 22 2004A flexible maximum-entropy component separation algorithm is presented that accommodates anisotropic noise, incomplete sky-coverage and uncertainties in the spectral parameters of foregrounds. The capabilities of the method are determined by first applying ... More
Power Spectrum of Primordial Inhomogeneity Determined from the 4-Year COBE DMR Sky MapsJan 12 1996Fourier analysis and power spectrum estimation of the cosmic microwave background anisotropy on an incompletely sampled sky developed by Gorski (1994) has been applied to the high-latitude portion of the 4-year COBE DMR 31.5, 53 and 90 GHz sky maps. Likelihood ... More
A Study of CAPTCHAs for Securing Web ServicesDec 23 2011Atomizing various Web activities by replacing human to human interactions on the Internet has been made indispensable due to its enormous growth. However, bots also known as Web-bots which have a malicious intend and pretending to be humans pose a severe ... More
Expected constraints on the Galactic magnetic field using PLANCK dataJan 27 2012We explore in this paper the ability to constrain the Galactic magnetic field intensity and spatial distribution with the incoming data from the Planck satellite experiment. We perform realistic simulations of the Planck observations at the polarized ... More
The joint large-scale foreground-CMB posteriors of the 3-year WMAP dataSep 07 2007Using a Gibbs sampling algorithm for joint CMB estimation and component separation, we compute the large-scale CMB and foreground posteriors of the 3-yr WMAP temperature data. Our parametric data model includes the cosmological CMB signal and instrumental ... More
Band Power Spectra in the COBE DMR 4-Year Anisotropy MapsJan 12 1996We employ a pixel-based likelihood technique to estimate the angular power spectrum of the COBE Differential Microwave Radiometer (DMR) 4-year sky maps. The spectrum is consistent with a scale-invariant power-law form with a normalization, expressed in ... More
HEALPix -- a Framework for High Resolution Discretization, and Fast Analysis of Data Distributed on the SphereSep 21 2004HEALPix -- the Hierarchical Equal Area iso-Latitude Pixelization -- is a versatile data structure with an associated library of computational algorithms and visualization software that supports fast scientific applications executable directly on very ... More
Joint 3D modelling of the polarized Galactic synchrotron and thermal dust foreground diffuse emissionMar 23 2010We present for the first time a coherent model of the polarized Galactic synchrotron and thermal dust emissions which are the main diffuse foreground for the measurement of the polarized power spectra of the CMB fluctuations with the Planck satellite ... More
Bayesian Power Spectrum Analysis of the First-Year WMAP dataJul 01 2004Dec 08 2004We present the first results from a Bayesian analysis of the WMAP first year data using a Gibbs sampling technique. Using two independent, parallel supercomputer codes we analyze the WMAP Q, V and W bands. The analysis results in a full probabilistic ... More
Bayesian analysis of the low-resolution polarized 3-year WMAP sky mapsMay 24 2007We apply a previously developed Gibbs sampling framework to the foreground corrected 3-yr WMAP polarization data and compute the power spectrum and residual foreground template amplitude posterior distributions. We first analyze the co-added Q- and V-band ... More
Power spectrum estimation from high-resolution maps by Gibbs samplingJul 01 2004Aug 23 2004We revisit a recently introduced power spectrum estimation technique based on Gibbs sampling, with the goal of applying it to the high-resolution WMAP data. In order to facilitate this analysis, a number of sophistications have to be introduced, each ... More
Comparing Polarised Synchrotron and Thermal Dust Emission in the Galactic PlaneFeb 01 2013As the next step toward an improved large scale Galactic magnetic field model, we present a simple comparison of polarised synchrotron and thermal dust emission on the Galactic plane. We find that the field configuration in our previous model that reproduces ... More
Comparing Polarised Synchrotron and Thermal Dust Emission in the Galactic PlaneFeb 01 2013Feb 20 2018As the next step toward an improved large scale Galactic magnetic field model, we present a simple comparison of polarised synchrotron and thermal dust emission on the Galactic plane. We find that the field configuration in our previous model that reproduces ... More
Bayesian component separation and CMB estimation for the 5-year WMAP temperature dataMar 25 2009A well-tested and validated Gibbs sampling code, that performs component separation and CMB power spectrum estimation, was applied to the {\it WMAP} 5-yr data. Using a simple model consisting of CMB, noise, monopoles and dipoles, a ``per pixel'' low-frequency ... More
Spherical Mexican Hat wavelet: an application to detect non-Gaussianity in the COBE-DMR mapsMay 07 2001The spherical Mexican Hat wavelet is introduced in this paper, with the aim of testing the Gaussianity of the Cosmic Microwave Background temperature fluctuations. Using the information given by the wavelet coefficients at several scales, we have performed ... More
Comparison of the COBE DMR and Tenerife DataNov 23 1994We have compared the Tenerife data with the {\it COBE} DMR two-year data in the declination +40\deg region of the sky observed by the Tenerife experiment. Using the Galactic plane signal at $\sim 30$ GHz, we show that the two data sets are cross-calibrated ... More
On the RMS Anisotropy at 7 degrees and 10 degrees Observed in the COBE-DMR Two Year Sky MapsAug 30 1994The frequency-independent RMS temperature fluctuations determined from the COBE-DMR two year sky maps are used to infer the parameter Q_{rms-PS}, which characterizes the normalization of power law models of primordial cosmological temperature anisotropy. ... More
Correlated Errors in the COBE DMR Sky MapsMar 10 1994The {\it COBE} DMR sky maps contain low-level correlated noise. We obtain estimates of the amplitude and pattern of the correlated noise from three techniques: angular averages of the covariance matrix, Monte Carlo simulations of two-point correlation ... More
Scale dependent non-Gaussianities in the CMB data identified with Minkowski Functionals and Scaling IndicesSep 23 2012In order to test for non-Gaussianities with respect to scale-dependencies we use so-called surrogate maps, in which possible phase correlations of the Fourier phases of the original WMAP data and simulations, respectively, are destroyed by applying a ... More
On Determining the Spectrum of Primordial Inhomogeneity from the COBE DMR Sky Maps: II. Results of Two Year Data AnalysisMar 31 1994A new technique of Fourier analysis on a cut sky (Gorski, 1994) has been applied to the two year COBE DMR sky maps. The Bayesian power spectrum estimation results are consistent with the Harrison-Zel'dovich n=1 model. The maximum likelihood estimates ... More
COBE-DMR-normalisation for Cold and Mixed Dark Matter Models Inflationary CosmogonyFeb 06 1995The two-year COBE-DMR 53 and 90 GHz sky maps in both ecliptic and galactic coordinates, are used to determine the normalisation of inflationary, flat, dark matter dominated universe models. The appropriately normalized cold and mixed dark matter models, ... More