Radio pulsars are rapidly rotating neutron stars that emit beams of radio waves, producing a highly regular train of pulses as the beam sweeps past Earth. When a pulsar is in a binary system orbiting a companion star, its apparent pulse frequency shifts due to the Doppler effect, making it much harder to detect in standard Fourier-based searches.

This simulator lets you explore those two key ideas. The time series shows intensity versus time: a periodic spike train representing the pulses as a radio telescope would record them, embedded in noise. The Fourier spectrum shows where the signal's power concentrates in frequency space — a sharp peak at the pulse frequency and its harmonics when the signal is coherent, which smears out when Doppler drift is applied.

This tool accompanies the study of a new semi-coherent detection method based on a hidden Markov model (HMM) designed to recover pulsars in compact binaries despite strong Doppler modulation. See the paper for full details:

O'Leary et al. (2026) — Discovering Radio Pulsars in Compact Binaries with a Hidden Markov Model, The Astrophysical Journal