Radio Emission from a Supernova Observed with Japanese and Korean Telescopes
Through radio observations using VLBI networks, a supernova discovered in a nearby galaxy has revealed that its progenitor star’s mass ejection activity had increased several decades before the explosion. This discovery, which was obtained by comparing the observational results with theoretical models, contributes to our understanding of massive star evolution and demonstrates the utility of small-scale VLBI networks in the research of transient astronomical events.
Supernovae are luminous astronomical phenomena caused by explosions of evolved massive stars. While they are typically observed in visible light, some supernovae emit radio waves as well. It is suggested that the interaction between the debris of the explosion and the circumstellar medium, which was ejected by a progenitor star before the explosion, generates radio emissions. By monitoring variability in radio brightness over time, we can infer variations in the density of circumstellar material and trace the mass-loss history of the progenitor star leading up to the explosion, shedding light on the evolutionary process of massive stars.
On May 19, 2023 (UTC), a Japanese amateur astronomer Koichi Itagaki discovered the supernova SN 2023ixf in the galaxy M101. This event, classified as a Type II supernova, is extraordinarily close, at a distance of approximately 22 million light-years from Earth. Since such close supernovae are rare, with only about one being discovered every decade, a number of worldwide research groups have conducted follow-up observations.
An international research team led by Yuhei Iwata, Project Assistant Professor from the Mizusawa VLBI Observatory (former Project Research Fellow, Division of Science), National Astronomical Observatory of Japan, observed SN 2023ixf using VERA, the Japanese VLBI Network (JVN), and the Korean VLBI Network (KVN). Utilizing the Hitachi 32-meter radio telescope operated by Ibaraki University and the Yamaguchi 34-meter radio telescope operated by Yamaguchi University, the JVN detected and measured radio emissions from the supernova at 152, 206, and 270 days after the explosion. Although VERA and KVN did not detect the emissions, they provided upper limits on radio intensity. By comparing these observations with theoretical models, the researchers inferred that the progenitor star gradually intensified its gas ejection activity over the 30 years leading up to the explosion.
Future VLBI observations aim to capture the gradual expansion of the radio emission region, enabling measurements of the explosion’s expansion dynamics. Additionally, conducting similar radio observations of other supernovae will help reveal the diversity of mass ejection in progenitor stars.
While the VLBI networks used in this study are smaller in scale compared to internationally collaborated VLBIs like the East Asian VLBI Network (EAVN) or the Event Horizon Telescope (EHT), their ability to perform rapid and frequent observations and utilize unique observation modes contributed to these findings. The next-generation radio telescope of the Square Kilometre Array (SKA) is expected to discover numerous transient events like supernovae through wide-field, high-sensitivity observations. This study demonstrates that small-scale VLBI networks will be valuable tools for studying the time evolution of transient phenomena in the SKA era.
This research was published in The Astrophysical Journal on 2025 January 8th, as “Radio Follow-up Observations of SN 2023ixf by Japanese and Korean Very Long Baseline Interferometers”.
Article Information
Yuhei Iwata, Masanori Akimoto, Tomoki Matsuoka, Keiichi Maeda, Yoshinori Yonekura, Nozomu Tominaga, Takashi J. Moriya, Kenta Fujisawa, Kotaro Niinuma, Sung-Chul Yoon, Jae-Joon Lee, Taehyun Jung, Do-Young Byun, “Radio Follow-up Observations of SN 2023ixf by Japanese and Korean Very Long Baseline Interferometers”, The Astrophysical Journal, 2025
DOI: https://doi.org/10.3847/1538-4357/ad9a62
Grant
This work was supported by JSPS KAKENHI grant (JP23K13151, JP20H01904, JP20H00174, JP24H01810, JP15H00784), the National Science and Technology Council, Taiwan (MOST 110-2112-M-001-068-MY3), the Academia Sinica, Taiwan (AS-CDA-111-M04), the National Research Foundation of Korea (NRF-2019R1A2C2010885).
