  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.
