Radio Observations of Microquasars with FAST

We report six radio observations of four microquasars—SS 433, GRS 1915+105, Cyg X-3 and MAXI J1820+070—conducted between 2022 and 2025 with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) using its pulsar backend, achieving a time resolution of 98.304 μs across an effective feed range of 1.04–1.45 GHz. A major focus of this work is the development of a standardized calibration pipeline for microquasar observations, including RFI mitigation, flux density, and polarization calibration, as well as multi-beam correlation inspections. Using On–Off mode and cross-beam verification, radio activity was detected in SS 433, GRS 1915+105 and Cyg X-3, while MAXI J1820+070 remained inactive. Both SS 433 and GRS 1915+105 show low linear polarization degrees of only a few percent. No credible quasi-periodic oscillations (QPOs) were detected in the 0.01–100 Hz range, suggesting that radio QPOs within this frequency range are relatively rare compared to those observed in the X-ray band. We therefore highlight the importance of future monitoring with high–time-resolution and high–sensitivity radio telescopes such as FAST, which will be crucial for revealing the correlation between jet and accretion processes and for uncovering the physical origin of QPOs.