Renovation of Seoul Radio Astronomy Observatory and Its First Millimeter VLBI Observations

TL;DR

This paper details the transformation of Seoul Radio Astronomy Observatory into a VLBI station, including hardware upgrades and successful initial millimeter-wave observations, advancing Korea's capabilities in high-resolution radio astronomy.

Contribution

The paper reports the first millimeter VLBI observations from SRAO after hardware upgrades, demonstrating its new capability as a VLBI station for high-frequency radio astronomy.

Findings

Successful detection of fringe at 86 GHz between SRAO and KVN Ulsan

Hardware and software upgrades enabled millimeter VLBI operations

Extension to 1 mm band and phase referencing techniques planned

Abstract

The Seoul Radio Astronomy Observatory (SRAO) operates a 6.1-meter radio telescope on the Gwanak campus of Seoul National University. We present the efforts to reform SRAO to a Very Long Baseline Interferometry (VLBI) station, motivated by recent achievements by millimeter interferometer networks such as Event Horizon Telescope, East Asia VLBI Network, and Korean VLBI Network (KVN). For this goal, we installed a receiver that had been used in the Combined Array for Research in Millimeter-wave Astronomy and a digital backend, including an H-maser clock. The existing hardware and software were also revised, which had been dedicated only to single-dish operations. After several years of preparations and test observations in 1 and 3-millimeter bands, a fringe was successfully detected toward 3C 84 in 86 GHz in June 2022 for a baseline between SRAO and KVN Ulsan station separated by 300 km. Thanks to the dual frequency operation of the receiver, the VLBI observations will soon be extended to the 1 mm band and verify the frequency phase referencing technique between 1 and 3-millimeter bands.