📋 Tender Overview
Physics and Mechanics Astronomy published an article introducing the research work carried out by a joint team composed of Wu Ziwei, a postdoctoral fellow of the Pulsar and Gravitational Physics Group of the National Astronomical Observatories, and researchers from the Max Planck Institute for Radio Astronomy in Germany, the Institute of Frontiers in Astronomy and Astrophysics of Beijing Normal University, and the University of Nevada. In this work, the scintillation arc phenomenon of fast radio bursts was discovered for the first time by analyzing the correlation of fast radio burst FRB 20220912A signals in time and frequency. This work shows that the changes in MHz bandwidth and minute order of magnitude in the frequency domain of fast radio bursts are caused by interstellar propagation effects, and the discovery of the scintillation arc phenomenon provides a new means to study the propagation medium and possible orbital motion of fast radio bursts.
Fast radio bursts are generally millisecond-sized radio bursts originating in other galaxies deep in the universe. Thousands of such outbreaks have been detected by radio telescopes around the world, and dozens of them will repeat them. The source of these repeated bursts is known as repeating fast radio bursts. The mechanism and origin of FRB production and celestial bodies is one of the most popular research directions in astrophysics. At present, the research focus of fast radio bursts is on their energy characteristics, polarization characteristics, multi-band observations, and host galaxy positioning. The study of FRB scintillation has always been a difficult point in this field, as James M. Cordes, a radio astronomer at Cornell University, pointed out in a review of the paper published in Science China at the same time: "So far, the FRB scintillation phenomenon has only been observed in a few sources, and the study of flickering is limited to the evolution of frequency, and the event rate of repeated FRB signals is too low to study the temporal correlation of scintillation structures." ”
As the largest single-antenna telescope at present, the high sensitivity of FAST is very suitable for interstellar scintillation studies of repeated FRBs. The team conducted multiple 1-hour observations of FRB 20220912A, and the event rate of bright bursts in individual observations was greater than 100 per hour. The extremely high event rate provided sufficient samples to study the temporal correlation of replicate FRBs, resulting in a complete dynamic spectrum of FRBs (left side of Figure 1). For the first time in the quadratic spectrum (the Fourier form of the dynamic spectrum), the team found that the geometric time delay and Doppler redshift of the FRB signal exhibit a simple quadratic relationship (scintillation arc phenomenon, right side of Figure 1). This phenomenon indicates that a thin layer of ionized interstellar medium dominates the scintillation phenomenon of FRB 20220912A. The team also predicted the corresponding scintillation arc curvature based on the current popular FRB origin model. Further compared with the observed scintillation arc curvature, we finally prefer that the scintillation arc of FRB 20220912A is generated by a medium within the Milky Way.
James M. Cordes further stated that "this method will be used as a very important means to understand FRB and its adjacent media, by finding and characterizing the interstellar medium within the FRB host galaxy and the Milky Way." The curvature of the scintillation arc depends on the effective velocity of the entire scintillation system and the relative position of the medium that dominates the scintillation phenomenon. If there is orbital motion in the FRB and the interstellar scintillation is dominated by the frb proximity medium, then the curvature of the scintillation arc will also show a corresponding periodic change. At present, the team is searching for non-annual changes in the scintillation arc curvature of FRBs based on FAST data, looking forward to finding direct observational evidence of the existence of orbital motion of FRBs, and continuing to explore the origin of FRBs.
