arXiv subjects

G. Walther

Publications and source records attributed to G. Walther.

4 recordsLinked to original sources

arXiv2005

Combined and Comparative Analysis of Power Spectra

In solar physics, especially in exploratory stages of research, it is often necessary to compare the power spectra of two or more time series. One may, for instance, wish to estimate what the power spectrum of the combined data sets might have been, or one may wish to estimate the significance of a particular peak that shows up in two or more power spectra. One may also on occasion need to search for a complex of peaks in a single power spectrum, such as a fundamental and one or more harmonics, or a fundamental plus sidebands, etc. Visual inspection can be revealing, but it can also be misleading. This leads one to look for one or more ways of forming statistics, which readily lend themselves to significance estimation, from two or more power spectra. We derive formulas for statistics formed from the sum, the minimum, and the product of two or more power spectra. A distinguishing feature of our formulae is that, if each power spectrum has an exponential distribution, each statistic also has an exponential distribution.

astro-ph↗

arXiv2004

Comment on "Search for periodic modulations of the solar neutrino flux in Super-Kamiokande" by J. Yoo et al

We comment on a recent article by Yoo et al. that presents an analysis of Super-Kamiokande 10-day and 5-day data, correcting certain errors in that article. We also point out that, in using the Lomb-Scargle method of power spectrum analysis, Yoo et al. ignore much of the relevant data. A likelihood analysis, that can take account of all of the relevant data, yields evidence indicative of modulation by solar processes.

hep-ph↗

arXiv1999

Rotational Signature and Possible R-Mode Signature in the GALLEX Solar Neutrino Data

Recent analysis of the Homestake data indicates that the solar neutrino flux contains a periodic variation that may be attributed to rotational modulation occurring deep in the solar interior, either in the tachocline or in the radiative zone. This paper presents an analysis of GALLEX data that yields supporting evidence of this rotational modulation at the 0.1% significance level. The depth of modulation inferred from the rotational signature is large enough to explain the neutrino deficit. The Rieger 157-day periodicity, first discovered in solar gamma-ray flares, is present also in Homestake data. A related oscillation with period 52 days is found in the GALLEX data. The relationship of these periods to the rotational period inferred from neutrino data suggests that they are due to r-mode oscillations.

astro-ph↗

arXiv1996

An Apparent Periodicity in the Gallex, Homestake and Kamiokande Neutrino Data

In order to explore a recent proposal that the solar core may contain a component that varies periodically with a period in the range 21.0 - 22.4 days, due either to rotation or to some form of oscillation, we have examined the time series formed from measurements of the solar neutrino flux by means of the GALLEX, Homestake and Kamiokande experiments. Direct Fourier transform analysis of the Homestake data shows that the most prominent peak in the entire spectrum (examined down to 5 days period) is found at a frequency of approximately 17.2 y-1 corresponding to a period of approximately 21.3 days. According to the "shuffle test," the probability of finding this large a peak in the prescribed search band is about 0.03%, if it is assumed that there is no correlation between count rate and time. The GALLEX and Kamiokande data are examined in a way that searches for similarity in the shapes of the two spectra in sliding windows in frequency. We find that the "spectral correlation measure" peaks at 17.2 y-1, and the shuffle test indicates that the probability of finding this large a peak at a specified frequency is 2%, if it is again assumed that for each time series there is no correlation between count rate and time. The combined significance estimate is of order 1 part in 105 that the results are due to chance, on the assumption that there is no real structure to the count-rate time series.

astro-ph↗