A Sample of Low-energy Bursts from FRB 121102

Abstract

We present 41 bursts from the first repeating fast radio burst discovered (FRB 121102). A deep search has allowed us to probe unprecedentedly low burst energies during two consecutive observations (separated by one day) using the Arecibo telescope at 1.4 GHz. The bursts are generally detected in less than a third of the 580-MHz observing bandwidth, demonstrating that narrowband FRB signals may be more common than previously thought. We show that the bursts are likely faint versions of previously reported multi-component bursts. There is a striking lack of bursts detected below 1.35 GHz and simultaneous VLA observations at 3 GHz did not detect any of the 41 bursts, but did detect one that was not seen with Arecibo, suggesting preferred radio emission frequencies that vary with epoch. A power law approximation of the cumulative distribution of burst energies yields an index −1.8 ± 0.3 that is much steeper than the previously reported value of ∼ −0.7. The discrepancy may be evidence for a more complex energy distribution. We place constraints on the possibility that the associated persistent radio source is generated by the emission of many faint bursts (∼ 700 ms −1 ). We do not see a connection between burst fluence and wait time. The distribution of wait times follows a log-normal distribution centered around ∼ 200 s; however, some bursts have wait times below 1 s and as short as 26 ms, which is consistent with previous reports of a bimodal distribution. We caution against exclusively integrating over the full observing band during FRB searches, because this can lower signal-to-noise.

Repeating fast radio bursts with WSRT/Apertif

“…Moving some bursts to a higher energy would flatten the distribution. Additionally, the energies probed by the data presented in Gourdji et al (2019) are lower than the others, where perhaps the slope is actually different or cannot be described by a power law at all. The slope is also strongly dependent on the chosen completeness threshold.…”

“…Law et al (2017) find a typical slope of −0.7 for VLA, GBT, and early Arecibo data. However, Gourdji et al (2019) find a significantly steeper slope of −1.8(3) using Arecibo data only, and suggest several reasons why the slope may be different. In some cases, the calculated burst energy is a lower limit.…”

“…there is only one burst rate during an active state, the wait time distribution is an exponential distribution. Samples of R1 wait times have indeed been shown to be consistent with exponential (Lin & Sang 2019), but also with log-normal (Gourdji et al 2019) and power-law (Lin & Sang 2019) distributions during the active state, where in some cases it is not possible to distinguish between these distributions.…”

A single fast radio burst localized to a massive galaxy at cosmological distance

“…It is difficult to assess the statistical significance of the non repetitions from a single burst source. While the repetition rate of FRB 121102 is poorly characterized, the activity appears to be clustered into week-month time scales (31,32) followed by long periods of inactivity. Sensitive searches with the Parkes radio telescope shortly after FRB 180924 was discovered did not detect any further bursts on week-month timescales.…”

A repeating fast radio burst source localized to a nearby spiral galaxy

“…Assuming similar beaming fractions, this makes them close to an order of magnitude less energetic compared to the weakest bursts seen from FRB 121102 to date 28 , and between four to six orders-ofmagnitude less energetic compared to FRB 180924 11 and FRB 190523 10 . Unless multiple models are invoked, a viable model for FRBs must address this large range of (apparent) energy outputs.…”