Browsing by Author "Jain, Pankaj"

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Angular power spectrum of CMB anisotropy from WMAP
(2011-08-09) Souradeep, Tarun; Saha, Rajib; Jain, Pankaj
The remarkable improvement in the estimates of diﬀerent cosmological parameters in recent years has been largely spearheaded by accurate measurements of the angular power spectrum of Cosmic Microwave Background (CMB) radiation. This has required removal of foreground contamination as well as detector noise bias with reliability and precision. Recently, a novel model independent method for the estimation of CMB angular power spectrum from multi-frequency observations has been proposed and implemented on the ﬁrst year WMAP (WMAP-1) data by Saha et al. 2006. We review the results from WMAP-1 and also present the new angular power spectrum based on three years of the WMAP data (WMAP-3). Previous estimates have depended on foreground templates built using extraneous observational input to remove foreground contamination. This is the ﬁrst demonstration that the CMB angular spectrum can be reliably estimated with precision from a self contained analysis of the WMAP data. The primary product of WMAP are the observations of CMB in 10 independent diﬀerence assemblies (DA) distributed over 5 frequency bands that have uncorrelated noise. Our method utilizes maximum information available within WMAP data by linearly combining DA maps from diﬀerent frequencies to remove foregrounds and estimating the power spectrum from the 24 cross power spectra of clean maps that have independent noise. An important merit of the method is that the expected residual power from unresolved point sources is signiﬁcantly tempered to a constant offset at large multipoles (in contrast to the ∼ L² contribution expected from a Poisson distribution) leading to a small correction at large multipoles. Hence, the power spectrum estimates are less susceptible to uncertainties in the model of point sources.
Blind estimation of the power spectrum of CMB anisotropy from WMAP
(2005-06-01) Saha, Rajib; Jain, Pankaj; Souradeep, Tarun
Accurate measurements of angular power spectrum of Cosmic Microwave Background (CMB) radiation has lead to marked improvement in the estimates of different cosmological parameters. This has required removal of foreground contamination as well as detector noise bias with reliability and precision. We present the estimation of CMB angular power spectrum from the multi-frequency observations ofWMAP using a novel model-independent method. The primary product of WMAP are the observations of CMB in 10 independent difference assemblies (DA) that have uncorrelated noise. Our method utilizes maximum information available within WMAP data by linearly combining all the DA maps to remove foregrounds and estimating the power spectrum from cross power spectra of clean maps with independent noise. We compute 24 cross power spectra which are the basis of the ﬁnal power spectrum. The binned average power matches with WMAP team’s published power spectrum closely. A small systematic difference at large multipoles is accounted for by the correction for the expected residual power from unresolved point sources. The correction is small and signiﬁcantly tempered. Previous estimates have depended on foreground templates built using extraneous observational input. This is the ﬁrst demonstration that the CMB angular spectrum can be reliably estimated with precision from a self contained analysis of the WMAP data.
CMB anisotropy power spectrum using linear combinations of WMAP maps
(2007-06-25) Saha, Rajib; Souradeep, Tarun; Jain, Pankaj; et al.
In recent years the goal of estimating diﬀerent cosmological parameters precisely has set new challenges in the eﬀort to accurately measure the angular power spectrum of CMB. This has required removal of foreground contamination as well as detector noise bias with reliability and precision. Recently, a novel model-independent method for the estimation of CMB angular power spectrum solely from multi-frequency observations has been proposed and implemented on the ﬁrst yearWMAP data by Saha et al. 2006. All previous estimates of power spectrum of CMB are based upon foreground templates using data sets from diﬀerent experiments. However our methodology demonstrates that CMB angular spectrum can be reliably estimated with precision from a self contained analysis of the WMAP data. In this work we provide a detailed description of this method. We also study and identify the biases present in our power spectrum estimate. We apply our methodoly to extract the power spectrum from the WMAP 1 year and 3 year data.
CMB Polarization and Temperature Power Spectra Estimation using Linear Combination of WMAP 5-year Maps
(2009-03-01) Souradeep, Tarun; Jain, Pankaj; Saha, Rajib; et al.
We estimate CMB polarization and temperature power spectra using WMAP 5-year foreground contaminated maps. The power spectrum is estimated by using a model independent method, which does not utilize directly the diﬀuse foreground templates nor the detec tor noise model. The method essentially consists of two steps, (i) removal of diﬀuse foregrounds contamination by making linear combination of individual maps in harmonic space and (ii) cross-correlation of foreground cleaned maps to minimize detector noise bias. For temperature power spectrum we also estimate and subtract residual unre- solved point source contamination in the cross-power spectrum using the point source model provided by the WMAP science team. Our 1TT, TE and EE power spectra are in good agreement with the published results of the WMAP science team. The error bars on the polarization power spectra, however, turn out to be smaller in comparison to what is obtained by the WMAP science team. We perform detailed numerical simulations to test for bias in our procedure. We ﬁnd that the bias is small in all cases. A negative bias at low l in TT power spectrum has been pointed in an earlier publication. We ﬁnd that the bias corrected quadrupole power (l(l + 1)Cl/2π) is 532 µK2, approximately 2.5 times the estimate (213.4 µK2) made by the WMAP team.
Model Independent Foreground Power Spectrum Estimation using WMAP 5-year Data
(2009-01-01) Ghosh, Tuhin; Saha, Rajib; Jain, Pankaj; et al.
In this paper, we propose & implement on WMAP 5-year data, a model independent approach of foreground power spectrum estimation for multifrequency observations of CMB experiments. Recently a model independent approach of CMB power spectrum estimation was proposed by Saha et al. 2006. This methodology demonstrates that CMB power spectrum can be reliably estimated solely from WMAP data without assuming any template models for the foreground components. In the current paper, we extend this work to estimate the galactic foreground power spectrum using the WMAP 5 year maps following a self contained analysis. We apply the model independent method in harmonic basis to estimate the foreground power spectrum and frequency dependence of combined foregrounds. We also study the behaviour of synchrotron spectral index variation over diﬀerent regions of the sky. We compare our results with those obtained from MEM foreground maps which are formed in pixel space. We ﬁnd that relative to our model independent estimates MEM maps overestimates the foreground power close to galactic plane and underestimates it at high latitudes.