A CHIME/FRB Study of Burst Rate and Morphological Evolution of the Periodically Repeating FRB 20180916B

FRB 20180916B is a repeating fast radio burst (FRB) with a 16.3 day periodicity in its activity. In this study, we present morphological properties of 60 FRB 20180916B bursts detected by CHIME/FRB between 2018 August and 2021 December. We recorded raw voltage data for 45 of these bursts, enabling microseconds time resolution in some cases. We studied variation of spectro-temporal properties with time and activity phase. We find that the variation in dispersion measure (DM) is less than or similar to 1 pc cm-3 and that there is burst-to-burst variation in scattering time estimates ranging from similar to 0.16 to over 2 ms, with no discernible trend with activity phase for either property. Furthermore, we find no DM and scattering variability corresponding to the recent change in rotation measure from the source, which has implications for the immediate environment of the source. We find that FRB 20180916B has thus far shown no epochs of heightened activity as have been seen in other active repeaters by CHIME/FRB, with its burst count consistent with originating from a Poissonian process. We also observe no change in the value of the activity period over the duration of our observations and set a 1 sigma upper limit of 1.5 x 10-4 day day-1 on the absolute period derivative. Finally, we discuss constraints on progenitor models yielded by our results, noting that our upper limits on changes in scattering and DM as a function of phase do not support models invoking a massive binary companion star as the origin of the 16.3 day periodicity.

Automated summary

This study presents the morphological properties of the repeating fast radio burst (FRB) FRB 20180916B, which exhibits a periodicity of 16.3 days. The variation in dispersion measure (DM) is found to be small, and there is no discernible trend in scattering time estimates with activity phase. The study also shows that FRB 20180916B has not displayed heightened activity periods and its burst count follows a Poissonian process. The results do not support the idea of a massive binary companion star as the origin of the 16.3 day periodicity.