Dispersion Measure Distribution of Unlocalized Fast Radio Bursts as a Probe of the Hubble Constant

Abstract

We present constraints on the Hubble constant ($H_0$) derived from the observed dispersion measure (DM) distribution of unlocalized fast radio bursts (FRBs). While localized FRBs with redshift measurements have been used to investigate the Hubble tension, their sample remains limited. Here we demonstrate that unlocalized FRBs -- which are far more numerous -- can independently constrain $H_0$ without requiring redshift information, as cosmic expansion imprints itself on their DM distribution. Analyzing a selected sample of 2124 unlocalized FRBs from the CHIME Catalog II, we obtain $H_0 = 73.8^{+14.0}_{-12.3}~\mathrm{km\,s^{-1}\,Mpc^{-1}}$ at the $1σ$ confidence level, corresponding to an uncertainty of about 18%. Breaking the degeneracy between $H_0$ and the characteristic cutoff energy $E_*$ of the FRB isotropic energy distribution would reduce this uncertainty to 9%. This work constitutes the first $H_0$ measurement derived solely from the DM distribution of unlocalized FRBs, highlighting their potential as a new cosmological probe. Future joint analyses with localized FRBs promise even tighter constraints.

Figures (2)

• Figure 1: Marginalized posterior distributions of $H_0$ from the unlocalized FRB sample: blue solid line for free $\lg E_*$, red solid line for $\lg E_*$ fixed at 40.9. For comparison, the purple and red shaded bands represent the $1\sigma$ constraints from the latest CMB inference ($H_0=67.24\pm0.35~\mathrm{km\,s^{-1}\,Mpc^{-1}}$) and the local distance indicators measurement ($H_0=73.50\pm0.81~\mathrm{km\,s^{-1}\,Mpc^{-1}}$), respectively.
• Figure 2: The 1D posterior distributions and 2D confidence regions (showing the $1\sigma$ and $2\sigma$ contours) for parameters $H_0$, $\mu_{\mathrm{host}}$, $\sigma_{\mathrm{host}}$, $\mathrm{DM_{halo}}$, $n$, $\gamma$, and $\lg E_*$, derived from 2124 unlocalized FRBs.