Epoch Folding Search for Periodicities (Application)
Application efs searches for periodicities with epoch folding in an input series. This is done folding the data over a range of periods and by searching for the maximun chi-square as a function of period. It is requires one input series. It is run in the Question/Answer user interface by typing:
[n]Xronos> efsin the Partial Question/Answer user interface by typing:
[n]Xronos> efs [series1]and in the Command-Driven user interface by typing:
[n]Xronos> efs/period=X[/qualifier1/qual2/... etc] [series1]where the /period= qualifier specifies the period over which the data are folded (in seconds if X>0 or days if X<0).
There are two important input parameters for folding applications: the epoch and the period over which the data will be folded. In folding applications the newbin time corresponds to the time duration of a phase bin in the folded light curve. This is determinated by the chosen number of phasebins per period. The default is such as to produce a folded light curve with 32 phasebins at maximum. The newbins per interval, together with the newbin time, determines the length of the time axis (an ``interval") over which a group of folded light curves is accumulated and their chi-square vs. period calculated. Note that no averaging of folded light curves in a frame is allowed: therefore each frame contains only the results from 1 interval.
The period resolutions is the spacing between two contiguous periods in the search: the default is half Fourier resolution in the interval (i.e. P*P/T(i)/2, where P is the trial period and T(i) the interval duration). If this is used a coherent periodicity will appear as a 1-2 bin broad peak in the chi-square vs. period plot.
The number of the default trial periods in the search are 128, but the number should be kept as small as possible in order to limit the execution time.
Error bars for the chi-square represent the standard deviation of the relevant chi-square distribution, rescaled by the value of the chi-square for each period divided by N-1, where N is the number of bins in the folded light curves.