Observational effects of banded repeating FRBs

TL;DR

This paper investigates how band-limited emission in repeating FRBs causes observational biases, affecting energy distribution analysis, and offers methods to correct for this incompleteness to better understand FRB properties.

Contribution

It introduces a simulation-based approach to quantify the bias caused by band-limited FRB emission and provides practical recommendations for more accurate energy distribution studies.

Findings

Band-limited emission causes detection incompleteness.

Energy distribution features like breaks and flattening can result from observational bias.

Using burst bandwidth instead of center frequency removes apparent bimodality.

Abstract

Recent observations have shown that repeating Fast Radio Bursts (FRBs) exhibit band-limited emission, whose frequency-dependent amplitude can be modeled using a Gaussian function. In this analysis, we show that banded emission of FRBs can lead to incompleteness across the observing band. This biases the detected sample of bursts and can explain the various shapes of cumulative energy distributions seen for repeating FRBs. We assume a Gaussian shape of the burst spectra and used simulations to demonstrate the above bias using an FRB 121102-like example. We recovered energy distributions that showed a break in power-law and flattening of power-law at low energies, based on the fluence threshold of the observations. We provide recommendations for single-pulse searches and analysis of repeating FRBs to account for this incompleteness. Primarily, we recommend that burst spectra should be modeled to estimate the intrinsic fluence and bandwidth of the burst robustly. Also, bursts that lie mainly within the observing band should be used for analyses of energy distributions. We show that the bimodality reported in the distribution of energies of FRB 121102 by Li et al. (2021) disappears when burst bandwidth, instead of the center frequency of the observation, is used to estimate energy. Sub-banded searches will also aid in detecting band-limited bursts. All the analysis scripts used in this work are available in a Github repository.