X-ray Polarization of the BL Lac Type Blazar 1ES 0229+200

TL;DR

This paper reports the first X-ray polarization measurements of the blazar 1ES 0229+200, revealing high polarization levels that support shock acceleration models but challenge existing turbulence-based theories.

Contribution

It provides the first X-ray polarization data for an extreme high synchrotron peaked blazar, offering new insights into its emission mechanisms.

Findings

X-ray polarization degree is 17.9% with a stable angle.

No significant variation in polarization with energy or time.

X-ray polarization is much higher than optical, indicating energy-stratified electron populations.

Abstract

We present polarization measurements in the $2-8 \thinspace \mathrm{keV}$ band from blazar 1ES 0229+200, the first extreme high synchrotron peaked source to be observed by the Imaging X-ray Polarimetry Explorer (IXPE). Combining two exposures separated by about two weeks, we find the degree of polarization to be $\Pi_{X} = 17.9 \pm 2.8 \%$ at an electric-vector position angle $\psi_X = 25.0 \pm 4.6^{\circ}$ using a spectropolarimetric fit from joint IXPE and XMM-Newton observations. There is no evidence for the polarization degree or angle varying significantly with energy or time on both short time scales (hours) or longer time scales (days). The contemporaneous polarization degree at optical wavelengths was $>$7$\times$ lower, making 1ES 0229+200 the most strongly chromatic blazar yet observed. This high X-ray polarization compared to the optical provides further support that X-ray emission in high-peaked blazars originates in shock-accelerated, energy-stratified electron populations, but is in tension with many recent modeling efforts attempting to reproduce the spectral energy distribution of 1ES 0229+200 which attribute the extremely high energy synchrotron and Compton peaks to Fermi acceleration in the vicinity of strongly turbulent magnetic fields.