Identifying the Origin of FRB-associated X-ray Bursts with X-ray Polarization

TL;DR

This paper investigates the origin of X-ray bursts associated with fast radio bursts by analyzing their polarization signatures, proposing that future X-ray polarization observations can distinguish between competing models.

Contribution

It introduces a method to differentiate models of XRBs associated with FRBs through polarization signatures, based on simulations and spectral fitting.

Findings

Different models predict distinct polarization patterns.

Polarization signatures vary with phase, time, and energy.

Future observations can test and identify the correct model.

Abstract

The origin of extraordinary X-ray burst (XRB) associated with a fast radio burst (FRB) like FRB 20200428D is still unclear, though several models such as the emission of a trapped fireball modified by resonant cyclotron scattering, the outflow from a polar trapped-expanding fireball, and the synchrotron radiation of a far-away relativistic shock, have been proposed. To determine which model is true, we study possible X-ray polarization signature for each model, inspired by the importance of radio polarization in identifying FRB origin. We first numerically simulate or calculate the XRB spectrum for each model and fit it to the observed data, then compute the corresponding polarization signal based on the fit. We find that these three models predict different polarization patterns in terms of phase/time and energy variations. The differences can be used to test the models with future X-ray polarization observations.