Histogram Analysis of Gallex, GNO and Sage Neutrino Data: Further   Evidence for Variability of the Solar Neutrino Flux
  If the solar neutrino flux were constant, as is widely assumed, the histogram of flux measurements would be unimodal. On the other hand, sinusoidal or square-wave modulation (either periodic or stochastic) may lead to a bimodal histogram. We here present evidence that the neutrino flux histogram is in fact bimodal. We analyze all available data from gallium experiments, coordinating results from the GALLEX and GNO experiments into one data set, and adopting results from the SAGE experiment as another data set. The two histograms, from the two data sets, are consistent in showing peaks in the range 45-75 SNU and 90-120 SNU, with a valley in between. By combining the data into one data set, we may form more detailed histograms; these strengthen the case that the flux is bimodal. A preliminary statistical analysis indicates that the bimodal character of the solar neutrino flux is highly significant. Since the upper peak is close to the expected flux (120-140 SNU), we may infer that the neutrino deficit is due to time-varying attenuation of the flux produced in the core. We estimate the time scale of this variation to be in the range 10-60 days. Attenuation that varies on such a time scale is suggestive of the influence of solar rotation, and points towards a process involving the solar magnetic field in conjunction with a nonzero neutrino magnetic moment. 
Peter A. Sturrock (Stanford) and Jeffrey D. Scargle (NASA-Ames)