2007 (IPP)

Permanent URI for this collectionhttp://localhost:4000/handle/11007/334

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    CMB power spectrum estimation with non-circular beam and incomplete sky coverage
    (2007-02-05) Mitra, Sanjit; Sengupta, Anand; Souradeep, Tarun; et al.
    Over the last decade, measurements of the CMB anisotropy has spearheaded the remarkable transition of cosmology into a precision science. However, addressing the systematic effects in the increasingly sensitive, high resolution, ‘full’ sky measurements from different CMB experiments pose a stiff challenge. The analysis techniques must not only be computationally fast to contend with the huge size of the data, but, the higher sensitivity also limits the simplifying assumptions which can then be invoked to achieve the desired speed without compromising the final precision goals. While maximum likelihood is desirable, the enormous computational cost makes the suboptimal method of power spectrum estimation using Pseudo-Cl unavoidable for high resolution data. The debiasing of the Pseudo-Cl needs account for non-circular beams, together with non-uniform sky coverage. We provide an analytic framework for correcting the power spectrum for the effect of beam noncircularity and non-uniform sky coverage (including incomplete/masked sky maps). The approach is perturbative in the distortion of the beam from non-circularity allowing for rapid computations when the beam is mildly non-circular. When non-circular beam effect is important, we advocate that it is computationally advantageous to employ ‘soft’ azimuthally apodized masks whose spherical harmonic transform die down fast with m.
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    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.