fBLS — a fast folding algorithm to produce BLS periodograms in search for transiting planets

We present fBLS – a novel technique for detecting transiting planets. fBLS is based on the fast-folding algorithm (FFA; Staelin 1969), extensively used in pulsar astronomy (e.g., Morello et al. 2020). fBLS simultaneously produces all the binned phase-folded lightcurves for an array of Np ‘sufficiently different’ trial periods, with O(Np*log(N)) arithmetic operations (while regular BLS requires O(Np*N) operations). We compute the standard BLS statistic for each folded lightcurve produced by fBLS, creating a standard BLS periodogram. We present fBLS capabilities by applying it to Kepler data, finding known and new planets. When applied to PLATO lightcurves, it will detect small rocky transiting planets, with periods shorter than one day, a period range for which the computation is extensive. fBLS will also be used to detect transiting planets with varying duration and transit timing.