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Likelihood Estimation (MLE) or a curve fit of the histogram via non-linear  least squares (NLSQ).  Both burst search and burst correction require knowledge of  background rates for all the different photon streams. Furthermore, we want to estimate the background  periodically (every few seconds) because it can varies vary  during the measurement on time scales of tens of seconds. FRETBursts splits the data in uniform time  slices called \textit{background periods} and computes the background rates for  each of these slices (see section~\ref{sec:bg_calc}). Note that the slicing