AAS 201st Meeting, January, 2003
Session 130. The Sun and Solar System Studies
Oral, Thursday, January 9, 2003, 10:00-11:30am, 618-619

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[130.02] Preliminary Time-Series Analysis of Super-Kamiokande Measurements of the Solar Neutrino Flux

P.A. Sturrock (Stanford University), D.O. Caldwell (UC Santa Barbara)

We report an analysis of an early release of Super-Kamiokande data comprising 184 bins, about 10 days each, from May 1996 to July 2001. Flux estimates vary over a range of more than 2:1, and the mean ratio of error estimates to flux estimates is 0.14. Due to the regularity of the binning, the power spectrum of the acquisition times has a huge peak (power S > 120) at frequency nu = 35.98, where frequencies are measured in cycles per year and power measurements are such that the probability of obtaining a peak of strength S or more by chance at a specified frequency is exp(-S). Such regularity inevitably leads to aliasing of a power spectrum.

The strongest peak in the range 0 - 100 in a power spectrum formed by a relative-likelihood procedure is at nu = 26.57 with S = 11.1. For the range 0 - 40, the second-strongest peak is at nu = 9.41 with S = 7.33. Since 26.57 + 9.41 = 35.98, it is probable that the weaker peak at 9.41 is an alias of the stronger at 26.57. Indeed, when we subtract the 26.57 oscillation from the data, the resulting "CLEAN" spectrum has no peak stronger than S >6.1 in the range 0 - 100, and none stronger than 5.5 in the range 0 - 40.

We note that 26.57 falls in the band 26.46 - 27.66, formed from twice the range of synodic rotation frequencies of an equatorial section of the solar convection zone. Such oscillations, attributable to "m = 2" structures, are not uncommon in solar data. We find from the shuffle test that the probability of obtaining a peak of S = 11.1 or more by chance in this band is 0.2%. This new result therefore supports previous evidence, found in Homestake and GALLEX-GNO data, for rotational modulation of the solar neutrino flux.

We thank the Super-Kamiokande consortium for making this data available. This work was supported by NSF grant AST-0097128 and DOE grant DE-FG03-91ER40618.

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.