Long trains of quasi-periodic microstructures in PSR J0034−0721

Abstract Pulsar microstructure probes the shortest coherent timescales of radio emission. Using extremely sensitive, high-time-resolution FAST observations of PSR J0034−0721 with a sampling rate of 8.192μs, we identified 33 trains of quasi-periodically oscillating micropulses. Strikingly, such micropulse trains consist of tens of micropulses, and the longest train has at least 143 micropulses. The characteristic quasi-period of quasi-periodic micropulses from these 33 trains is $89^{+88}_{-44}$ μs, one magnitude smaller than the expected value from the famous empirical Pμ–P0 relation given by Kramer et al. (2024).