A bright burst detected by Swift’s Burst Alert Telescope on 2020 March 12 led to the discovery of the magnetar Swift J1818.0‑1607. The quiescent radio signal from the neutron star was first recorded a week later with the Shanghai Tian Ma Radio Telescope (TMRT). The telescope observed simultaneously at 2.25 and 8.60 GHz from Modified Julian Dates (MJDs) 58936 to 59427. The pulse shapes changed noticeably over time, indicating that the three emission components—the leading, central and trailing peaks—moved in relative strength.

During this monitoring window the magnetar’s spin slowed at an average rate of –1.65 × 10⁻¹¹ s⁻², but the magnitude of that slowdown first rose and then fell. Around MJD 59030–59050 the radio spectrum flattened from a steep index of about –1.8 to nearly zero before oscillating again. The strongest signal came from the 2.25 GHz band, peaking at 7.11 mJy on MJD 59208, while 8.60 GHz reached 3.70 mJy at the same date.

These data show that the torque on the star varied substantially, so a single constant spin‑down rate does not describe the full active period. Even the two‑point spectral index measurements are biased: only epochs with detections in both bands were used, which can hide steep‑spectrum episodes at 8.60 GHz.

The results illustrate how a magnetar’s radio loudness and rotation can evolve on timescales of weeks to months, suggesting that both magnetospheric changes and internal physics drive the observed variability.