Exploring local fNL estimators based on the binned bispectrum

Abstract

We explore different estimators of the local non-linear coupling parameter, fNL, based on the binned bispectrum presented in Bucher et al. Using simulations of Wilkinson Microwave Anisotropy Probe (WMAP)-7-year data, we compare the performance of a regression neural network with a Χ2-minimization and study the dependence of the results on the presence of the linear term in the analysis and on the use of inpainting for masked regions. Both methods obtain similar results and are robust to the use of inpainting, but the neural network estimator converges considerably faster. We also examine the performance of a simplified Χ2 estimator that assumes a diagonal matrix and has the linear term subtracted, which considerably reduces the computational time; in this case inpainting is found to be crucial. The estimators are also applied to real WMAP-7-year data, yielding constraints at 95 per cent confidence level of-3< fNL < 83. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.