Energy and waiting time distributions of FRB 121102 observed by FAST

TL;DR

This study analyzes the energy and waiting time distributions of FRB 121102 using FAST data, revealing power-law behaviors, epoch-dependent energy distributions, and a Weibull distribution for waiting times, shedding light on the burst mechanisms.

Contribution

It provides the first detailed analysis of energy and waiting time distributions of FRB 121102 with a large FAST sample, highlighting epoch-dependent energy behaviors and burst timing patterns.

Findings

High-energy distribution follows a power-law with index -1.86.

Energy distributions differ before and after MJD 58740.

Waiting times are well modeled by a Weibull distribution with specific parameters.

Abstract

The energy and waiting time distributions are important properties for understanding the physical mechanism of repeating fast radio bursts (FRBs). Recently, the Five-hundred-meter Aperture Spherical radio Telescope (FAST) detected the largest burst sample of FRB 121102, containing 1652 bursts. We use this sample to investigate the energy and waiting time distributions. The energy count distribution $dN/dE$ at the high-energy range ($>10^{38}$ erg) can be fitted with a single power-law function with an index of $-1.86 ^{+0.02}_{-0.02}$, while the distribution at the low-energy range deviates from the power-law function. An interesting result of Li et al. (2021) is that there is an apparent temporal gap between early bursts (occurring before MJD 58740) and late bursts (occurring after MJD 58740). We find the energy distributions of high-energy bursts at different epochs are inconsistent. The power-law index is $-1.70^{+0.03}_{-0.03}$ for early bursts and $-2.60^{+0.15}_{-0.14}$ for late bursts. For bursts observed in a single day, a linear repetition pattern is found. We use the Weibull function to fit the distribution of waiting time of consecutive bursts. The shape parameter $k = 0.72^{+0.01}_{-0.01}$ and the event rate $r = 736.43^{+26.55}_{-28.90}$ day$ ^{-1} $ are derived. If the waiting times with $\delta_t < 28$ s are excluded, the burst behavior can be described by a Poisson process. The best-fitting values of $k$ are slightly different for low-energy ($E < 1.58\times10^{38}$ erg) and high-energy ($E > 1.58\times10^{38}$ erg) bursts.