Are There Multiple Populations of Fast Radio Bursts?

Abstract

The repeating FRB 121102 (the "repeater") shows repetitive bursting activities and was localized in a host galaxy at z = 0.193. On the other hand, despite dozens of hours of telescope time spent on follow-up observations, no other fast radio bursts (FRBs) have been observed to repeat. Yet, it has been speculated that the repeater is the prototype of FRBs, and that other FRBs should show similar repeating patterns. Using the published data, we compare the repeater with other FRBs in the observed time interval (Δt)-flux ratio (S <inf>i</inf>/S <inf>i+1</inf>) plane. We find that whereas other FRBs occupy the upper (large S <inf>i</inf>/S <inf>i+1</inf>) and right (large Δt) regions of the plane due to the non-detections of other bursts, some of the repeater bursts fall into the lower left region of the plot (short interval and small flux ratio) excluded by the non-detection data of other FRBs. The trend also exists even if one only selects those bursts detectable by the Parkes radio telescope. If other FRBs were similar to the repeater, our simulations suggest that the probability that none of them have been detected to repeat with the current searches would be ∼(10^-4-10^-3). We suggest that the repeater is not representative of the entire FRB population, and that there is strong evidence of more than one population of FRBs.