Oral Presentation

Simultaneous observations of an active repeater FRB 20240114A with Lulin One-meter Telescope and FAST

Author(s): Tetsuya Hashimoto (NCHU), Tomotsugu Goto (NTHU), Chow-Choong Ngeow (NCU), Chen-hui Niu (Central China Normal University), Yuhao Zhu (Chinese Academy of Sciences), Tsung-Ching Yang (NCHU), Bjorn Jasper R. Raquel (University of Philippines), Howard Chuang (NCHU), William Chang (NCHU), Simon C.-C. Ho (ANU), Shotaro Yamasaki (NCHU), Tzu-Yin Hsu (NTHU), Mohanraj Madheshwaran (NCHU), Yuu Niino (University of Tokyo), Ece Kilerci (Sabanci University), Yu-An Chen (NTHU)

Presenter: Tetsuya Hashimoto (NCHU)

The radiation mechanism of fast radio bursts (FRBs) remains unknown. Because currently-survived theoretical models can basically explain the common features of FRBs in radio, including their short timescales and extremely high brightness temperatures, solely using radio data is not effective in distinguishing FRB models. Simultaneously detected optical counterparts of FRBs are the final piece of the puzzle to uncover their mysterious radiation mechanism because major theoretical FRB models, i.e., magnetosphere and external shocks, predict significantly different optical-to-radio fluence ratios. However, the hypothetical optical counterpart is yet to be detected because FRBs disappear in ~1 ms, making the simultaneous counterpart search challenging. To overcome this problem, we take advantage of monitoring observations by the Five-hundred-meter Aperture Spherical Telescope (FAST). FAST is the most sensitive single-dish radio telescope, regularly monitoring known repeating FRB sources. Once its monitoring is scheduled, we trigger simultaneous Target-of-Opportunity (ToO) observations with the Lulin One-meter Telescope (LOT; optical) in Taiwan, using a CMOS camera with a time resolution of ~17 ms. This is one of the shortest timescales conducted by CMOS cameras for FRBs so far, enhancing the sensitivity to the optical counterpart. In 2024, we triggered two ToO observations of LOT to conduct simultaneous observations of FRB 20240114A during part of the FAST's monitoring campaign. FRB 20240114A was first discovered by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and is known as an active repeater. More than 17 (61) FRBs were detected with FAST on 7 (14) July during the LOT ToO observations. Based on the non-detection of optical counterparts to these bursts, the brightest case of the magnetospheric scenario of the optical counterpart is excluded.