Low-frequency VLBI observation with Iitate, Zao, and Toyokawa observatory

The study demonstrates the first low-frequency VLBI using a compact, disk-based K5/VSSP system with offline FX-type correlation for high-resolution radio astronomy. Using three stations in Japan (Iitate, Zao, and Toyokawa) equipped with K5/VSSP recorders, the team observed the bright calibrator source 3C147 at 327 MHz to test system stability and fringe detection. Successful detection of strong fringes across all baselines confirmed coherent signal synchronization and robust frequency stability, despite ionospheric and radio interference challenges. The use of an offline FX-type software correlator on a general-purpose workstation proved effective for low-frequency data analysis. These results validate the technical readiness of compact, affordable VLBI systems for sub-GHz observations. The experiment lays essential groundwork for future global low-frequency VLBI networks, including collaboration with facilities such as GMRT, to spatially separate stellar and planetary radio emissions and to search for auroral radio bursts from exoplanets.