Joint Time-Series Analysis of Homestake and GALLEX-GNO Solar Neutrino Data: Evidence for Rieger-Type Periodicities and their Interpretation as R-Mode Oscillations

Abstract

Previous power-spectrum analyses of the Homestake and GALLEX-GNO radiochemical solar neutrino data have shown evidence of the effects of solar rotation and also indications of oscillations with two periods that are well known in solar physics: one at about 154 days period (the Rieger periodicity) and another at about 52 days period. We here analyze both data sets, taken together, to test the hypothesis that the above periodicities, and a related periodicity with a period of about 77 days, are due to r-mode oscillations with spherical harmonic indices l = 3 and m = 1, 2, and 3. These would have frequencies nuR/6, nuR/3, and nuR/2, where nuR is the sidereal rotation rate where the waves are excited. We first form a statistic that combines information from power spectra formed from Homestake and GALLEX-GNO data. From this statistic, we form another statistic to search for a sidereal rotation frequency that leads simultaneously to four peaks in the Homestake-GALLEX-GNO spectrum: one corresponding to the synodic rotation frequency nuR - 1, and the other three corresponding to the l = 3 r-modes. We find that, in the range 0 to 20 cycles per year, there is one notable peak at 13.88 cycles per year; This falls in the rotation frequency range of the radiative zone. The corresponding synodic rotation period is 28.4 days, and the corresponding r-mode periods are 157, 78, and 52 days. By applying the shuffle test to the data, we find that the probability of obtaining by chance a peak this big or bigger in the rotation-frequency band of the radiative-zone is less than 0.1%. The modulation of the neutrino flux is attributed to the poloidal motion of a magnetic structure that moves in and out of the narrow beam of neutrinos that originate in the solar core and are detected on Earth.