Observations of Low and Intermediate Spectral Peak Blazars with the Imaging X-ray Polarimetry Explorer

TL;DR

This study used IXPE to observe four blazars, setting upper limits on their X-ray polarization, which supports models where unpolarized photons dominate the X-ray emission in these objects.

Contribution

First X-ray polarization upper limits for low and intermediate spectral peak blazars, constraining emission models and informing jet physics.

Findings

No significant X-ray polarization detected at 3σ level.

Upper limits on polarization degree are approximately 10-30%.

Results favor unpolarized photon dominance in X-ray emission.

Abstract

We present X-ray polarimetry observations from the Imaging X-ray Polarimetry Explorer (IXPE) of three low spectral peak and one intermediate spectral peak blazars, namely 3C 273, 3C 279, 3C 454.3, and S5 0716+714. For none of these objects was IXPE able to detect X-ray polarization at the 3$\sigma$ level. However, we placed upper limits on the polarization degree at $\sim$10-30\%. The undetected polarizations favor models where the X-ray band is dominated by unpolarized photons upscattered by relativistic electrons in the jets of blazars, although hadronic models are not completely eliminated. We discuss the X-ray polarization upper limits in the context of our contemporaneous multiwavelength polarization campaigns.