2026ApJ...998..183O

Discovering radio pulsars in compact binaries, whose orbital periods P_b satisfy P_b ≲ 1 day, is computationally challenging, because the time-dependent pulse frequency f_p(t) is strongly Doppler modulated by the binary motion. Here we present a new, fast, semi-coherent detection scheme based on a hidden Markov model (HMM) combined with a maximum-likelihood matched filter, the Schuster periodogram. The HMM scheme complements traditional acceleration searches by dividing f_p(t) into piecewise-constant blocks and tracking the block-to-block evolution efficiently using dynamic programming. Monte Carlo simulations show that the new method can detect compact binaries with flux densities S ≥ 0.50 mJy and orbital periods P_b ≥ 0.012 day under observing conditions (e.g., cadence) typical of radio pulsar surveys, with and without impulsive, narrowband radio-frequency interference. The new method is fast; it employs the classic Viterbi algorithm to solve the HMM recursively. The central processing unit runtime scales nominally as ${T}_{{\rm{run}}}\approx 2.8\,{N}_{B}({N}_{T}/1{0}^{2})({N}_{Q}\mathrm{ln}{N}_{Q}/1{0}^{4}\mathrm{ln}1{0}^{4})\,{\rm{s}}$ for N_B subbands, N_T coherent segments, and N_Q frequency bins.