Evidence for a Damped Millisecond Quasi-Periodic Structure in a Fast Radio Burst
Fast radio bursts (FRBs) are millisecond-duration transients of unknown origin, likely associated with compact astrophysical objects. We report evidence for a damped millisecond quasi-periodic structure in a non-repeat FRB~20190122C. The burst consists of eight closely spaced radio pulses separated by $\sim$1 ms, with pulse amplitudes exhibiting an exponential decay starting from the brightest component. Combined Gaussian fitting and time-series analysis reveal a quasi-periodic oscillation (QPO) at $\sim$1 kHz. The observed QPO is consistent with damped magnetospheric oscillations. Assuming an Alfvén wave origin, we estimate a surface magnetic field of $\sim 10^{12}$ G and a characteristic spin period of $\sim$1 s, favoring a low-field magnetar or young neutron star scenario. The absence of frequency drift and the presence of exponential damping disfavor a merger-driven origin. These results suggest the first detection of an exponentially decaying QPO in any FRB, marking a rare detection of coherent oscillatory behavior in FRBs.