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Abstract: The arrival time distribution of cosmic ray events is well suited to extractinformation regarding sky anisotropies. For an experiment with nearly constantexposure, the frequency resolution one can achieve is given by the inverse ofthe time $T$ during which the data was recorded. For $T$ larger than onecalendar year the resolution becomes sufficient to resolve the sidereal anddiurnal frequencies. Using a Fourier expansion on a modified time parameter, weshow in this note that one can accurately extract sidereal modulations withoutknowledge of the experimental coverage. This procedure also gives the fullfrequency pattern of the event sample under studies which contains importantinformation about possible systematics entering in the sidereal analysis. Wealso show how this method allows to correct for those systematics. Finally, weshow that a two dimensional analysis, in the form of the spherical harmonic$Y l^m$ decomposition, can be performed under the same conditions for all$m e 0$.



Author: Pierre Billoir, Antoine Letessier-Selvon

Source: https://arxiv.org/



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