A new limit on intergalactic magnetic fields on sub-kpc scales from fast radio bursts

TL;DR

This paper uses FRB scattering data to set new upper limits on intergalactic magnetic fields on sub-kiloparsec scales, revealing the presence of weak magnetic fields in the IGM at redshifts 1-2.

Contribution

It introduces a novel method to constrain small-scale magnetic fields in the IGM using FRB scattering measurements, extending beyond traditional Rotation and Dispersion Measure techniques.

Findings

Upper limits of 10-30 nG on magnetic fields at 0.07-0.20 kpc scales.

Nonmagnetized IGM cannot explain observed scattering at all redshifts.

Warm-Hot IGM component marginally consistent with data at z ~ 1.

Abstract

We use the measured scattering timescales of Fast Radio Bursts (FRBs) from the CHIME catalog to derive an upper limit on the magnetic field on sub-kpc scales in the intergalactic medium (IGM). A nonmagnetized, photoionized IGM is insufficient to explain the turbulent scattering at all redshifts, with a Warm-Hot component being marginally consistent with the data at $z \sim 1$. Accounting for the lower envelope of the temporal smearing distribution with a nonzero magnetic field leads to upper limits $B < 10-30$ nG on scales of 0.07-0.20 kpc in the IGM at $z \sim 1-2$. Our work introduces a novel technique to constrain small-scale magnetic fields in the IGM, in a regime unexplored by the Rotation and Dispersion Measures of FRBs.