Revealing the cosmic reionisation history with fast radio bursts in the era of Square Kilometre Array

Abstract

Revealing the cosmic reionisation history is at the frontier of extragalactic astronomy. The power spectrum of the cosmic microwave background (CMB) polarisation can be used to constrain the reionisation history. Here we propose a CMB-independent method using fast radio bursts (FRBs) to directly measure the ionisation fraction of the intergalactic medium (IGM) as a function of redshift. FRBs are new astronomical transients with millisecond timescales. Their dispersion measure (DM IGM ) is an indicator of the amount of ionised material in the IGM. Since the differential of DM IGM against redshift is proportional to the ionisation fraction, our method allows us to directly measure the reionisation history without any assumption on its functional shape. As a proof of concept, we constructed mock non-repeating FRB sources to be detected with the Square Kilometre Array, assuming three different reionisation histories with the same optical depth of Thomson scattering. We considered three cases of redshift measurements: (A) spectroscopic redshift for all mock data, (B) spectroscopic redshift for 10% of mock data, and (C) redshift estimated from an empirical relation of FRBs between their time-integrated luminosity and rest-frame intrinsic duration. In all cases, the reionisation histories are consistently reconstructed from the mock FRB data using our method. Our results demonstrate the capability of future FRBs in constraining the reionisation history.

Constraining the Epoch of Reionization With Highly Dispersed Fast Radio Bursts

“…While high-DM (DM > 4000) events have not yet been observed, Connor (2019) notes that one can design an experiment that has a higher detection rate of highly dispersed events by trading time resolution for higher frequency resolution. Zhang et al (2021) note that FAST and SKA will have the capability of making such detections and most recently Hashimoto et al (2021) show that observations from SKA phase 2 will indeed reveal our reionization history. It must be noted, however, that the FRB progenitor will ultimately dictate whether there exists an FRB population during the EoR.…”

“…The way in which the mean DM depends on the broad timeline of the reionization history has been previously studied (Hashimoto et al 2021;Zhang et al 2021;Beniamini et al 2021;Macquart 2018). Most recently, Hashimoto et al (2021) show that one year's worth of observing with SKA phase 2 can reveal our cosmic reionization history, and Beniamini et al (2021) show that both DM and the differential FRB source count distribution prove useful probes of reionization even with limited redshift information. In this paper we build on the techniques outlined by these authors by performing a study of how the morphology, astrophysics and evolution of the EoR affect the mean DM of high redshift FRBs.…”

What it Takes to Measure Reionization with Fast Radio Bursts

“…Second, high-redshift FRBs are expected to be sensitive cosmological probes. Theoretical predictions show that a population of FRBs at 𝑧 ∼ 3 − 4 could be used to probe second helium reionization happening around redshift 𝑧 ≈ 3.5 [56][57][58][59][60], while signals from 𝑧 > 5 would primarily trace variation in the ionization state of hydrogen atoms, and, consequently, could be used to probe the Epoch of Reionization [EoR,12,[61][62][63][64][65]. Such measurements would help to constrain the total optical depth of the Cosmic Microwave Background (CMB), 𝜏, to a higher accuracy than what is presently achievable [12,[61][62][63].…”

“…Although the importance of high-redshift FRBs as the EoR probes has been praised in literature [12,[62][63][64][65], existing works make assumptions that either lead to biases in the results or limit the constraining power of the data. Fialkov & Loeb [12] were the first to point out that FRBs could be used as precision probes of the EoR and performed a simplified error analysis to estimate the expected accuracy on 𝜏 (a similar analysis was performed by Beniamini et al [62]), which stimulated further studies.…”

“…Fialkov & Loeb [12] were the first to point out that FRBs could be used as precision probes of the EoR and performed a simplified error analysis to estimate the expected accuracy on 𝜏 (a similar analysis was performed by Beniamini et al [62]), which stimulated further studies. Beniamini et al [62] and Hashimoto et al [64] constrain the ionized fraction by grouping FRBs into redshift bins and considering the difference between neighboring DM bin-averages. As a result of binning, redshifts and DMs of the individual FRBs are lost and with them the capabilities to smoothly trace the EoR.…”