Demodulation of RHESSI count rates by an unbiased linear Bayes estimator

Abstract

The RHESSI experiment uses rotational modulation for x- and gamma ray imaging of solar eruptions. In order to disentangle rotational modulation from intrinsic time variation, an unbiased linear estimator for the spatially integrated photon flux is proposed. The estimator mimics a flat instrumental response under a gaussian prior, with achievable flatness depending on the counting noise. The amount of regularization is primarily given by the modulation-to-Poisson levels of fluctuations, and is only weakly affected by the Bayesian prior. Monte Carlo simulations demonstrate that the mean relative error of the estimator reaches the Poisson limit, and real-data applications are shown.