Returns p-value of a frequency peak according to pbaluev (2008) given Z, fmax and tm. Reused from the LOMB library (https://rdrr.io/cran/lomb/)
pbaluev(Z, fmax, tm)
an intermediate calculation step needed to compute the p-value according to pbaluev (2008).
the power of the frequency
the maximum frequency in the spectrum
the time grid of the original time series