The IXPE and multifrequency polarimetric view of the extreme blazars 1ES 1101-232 and RGB J0710+591

TL;DR

This study uses multiwavelength polarimetry from radio to X-rays to investigate the magnetic field structures in the jets of two extreme BL Lac objects, revealing frequency-dependent polarization behaviors and proposing an improved shock model.

Contribution

It provides new multiwavelength polarization measurements of two EHBL blazars and introduces an enhanced stratified shock model to explain the observed polarization properties.

Findings

Strong frequency dependence of polarization in 1ES 1101-232

Upper limit of X-ray polarization in RGB J0710+591

Model successfully reproduces observed polarization data

Abstract

Multiwavelength polarimetry is a powerful tool to probe magnetic field and flow geometries in the relativistic jets of blazars. In this respect, particularly interesting are the sources whose synchrotron emission covers a broad range of frequencies, from radio to X-rays, such as the BL Lac objects of the HSP type. Previous measurements including radio, optical and X-ray data show a clear trend, with the degree of polarization increasing with frequency. Here we report radio, optical and X-ray observations ($Swift$, $Nustar$ and $IXPE$) of 1ES 1101-232 and RGB J0710+591, two blazars belonging to the puzzling subclass of extreme BL Lacs (EHBL). For 1ES 1101-232 we found a strong frequency-dependency of the degree of polarization (with a ratio $\Pi_X/\Pi_O\simeq 5.2$). For RGB J0710+591, IXPE derived a 1$\sigma$ upper limit $\Pi_X<11.6\%$, comparable with the measured optical degree of polarization (average $\Pi_O\sim 12\%$). We discuss the results in the framework of current interpretations and, in particular, we report an improved version of the stratified shock model that is able to reproduce the observed data of both sources.