Constraining the Epoch of Reionization With Highly Dispersed Fast Radio Bursts

Abstract

The period in which hydrogen in the intergalactic medium (IGM) is ionized, known as the Epoch of Reionization (EoR) is still poorly understood. The timing and duration of the EoR is expected to be governed by the underlying astrophysics. Furthermore, most models of reionization predict a correlation between the density and ionization field. Here we consider using the mean dispersion measure (DM) of high redshift Fast Radio Bursts (FRBs) as a probe of the underlying astrophysics and morphology of the EoR. To do this, we forecast observational scenarios by building mock data sets of non-repeating FRBs between redshifts 8 ≤ 𝑧 ≤ 10. It is assumed that all FRBs have accompanying spectroscopic redshift measurements. We find that samples of 100 high redshift FRBs, in the above mentioned narrow redshift range, can rule out uncorrelated reionization at 68% credibility, while larger samples, ≥ 10 4 FRBs, can rule out uncorrelated reionization at 95% credibility. We also find 100 high redshift FRBs can rule out scenarios where the Universe is entirely neutral at 𝑧 = 10 with 68% credibility. Further with ≥ 10 5 FRBs, we can constrain the duration Δ𝑧 of reionization (duration between mean ionized fraction 0.25 to 0.75) to Δ𝑧 = 2.0 +0.5 −0.4 , and the midpoint of reionization to 𝑧 = 7.8 +0.4 −0.2 at 95% credibility.

A new measurement of the Hubble constant using Fast Radio Bursts

“…Since the DM is a noisy distance estimate, FRBs with known host can be used to compile a DM -redshift relation. This turns FRBs into standardisable radio transmitters, which can be used to probe the baryon content of the Universe at late times (Walters et al 2019;Macquart et al 2020), the ionisation history of the IGM (Jaroszynski 2019;Bhattacharya et al 2020;Pagano & Fronenberg 2021) or the current expansion rate (Wu et al 2020).…”

Search for the correlations between host properties and ${\rm DM_{host}}$ of fast radio bursts: constraints on the baryon mass fraction in IGM

“…Qiang et al [44] showed that FRBs can be used to test the possible cosmic anisotropy. Pagano & Fronenberg [45] pointed out that the highly dispersed FRBs can be used to constrain the epoch of cosmic reionization. Pearson et al [46] showed that strongly lensed repeating FRBs can be used as the probes to search for gravitational waves.…”

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.…”

“…Furthermore, in the absence of a functional form for the reionization history, this approach does not permit imposing global relationships (such as the monotonicity of the reionization history) across large redshift ranges. Another approach was taken by Zhang et al [63] and Pagano & Fronenberg [65] who postulate a specific shape of the reionization history, either the popular tanh function or a simulationbased form. Because the actual EoR history is unknown, such assumptions lead to biased results.…”