Fast radio bursts (FRBs) are intense, short-duration radio transients of mysterious origin. They have been detected across a wide range of frequencies from 110 MHz to 8 GHz. Their spectral properties, remaining poorly understood, are essential for understanding the intrinsic radiation mechanism and propagation effects. Here, we report the discovery of a periodic modulation in the central emission frequency of FRB 20240114A, based on more than one thousand bursts collected by an ultra-wideband receiving system. The burst central frequencies reveals a significant modulation with a period of ∼112 days. The statistical significance of this detected periodicity exceeds 6σ for both the Lomb-Scargle and phase-folding methods. Within a single period, the central emission frequency exhibits a systematic drift from lower to higher values. We evaluate several physical mechanisms for this unique spectral evolution. The free-free absorption together with cyclotron resonant absorption in a binary system or free precession models could potentially explain such behavior. The discovery of this periodic frequency modulation unveils a new layer of complexity in the underlying radiation mechanism and propagation effect of FRBs.
@article{arxiv.2605.12098,
title = {Periodic Emission Frequency Modulation in a Hyperactive Fast Radio Burst},
author = {Rui-Nan Li and Hao-Tian Lan and Zhen-Yin Zhao and Qin Wu and Fa-Yin Wang and Zi-Gao Dai},
journal= {arXiv preprint arXiv:2605.12098},
year = {2026}
}