Magnetic halos of galaxies are crucial for understanding galaxy evolution,galactic-scale outflows, and feedback from star formation activity. Identifyingthe magnetised halo of the Milky Way is challenging because of the potentialcontamination from foreground emission arising in local spiral arms.Additionally, it is unclear how our magnetic halo is influenced by recentlyrevealed large-scale structures such as the X-ray emitting eROSITA Bubbles.Here we report the identification of several kpc-scale magnetised structuresbased on their polarized radio emission and their gamma-ray counterparts, whichcan be interpreted as the radiation of relativistic electrons in the Galacticmagnetic halo. These non-thermal structures extend far above and below theGalactic plane and are spatially coincident with the thermal X-ray emissionfrom the eROSITA Bubbles. The morphological consistency of these structuressuggests a common origin, which can be sustained by Galactic outflows driven byactive star-forming regions located in the Galactic Disc at 3-5 kpc from theGalactic Centre. These results reveal how X-ray-emitting and magnetised halosof spiral galaxies can be related to intense star formation activities andsuggest that the X-shaped coherent magnetic structures observed in their haloscan stem from galaxy outflows.
The X-ray polarization observations made possible with the Imaging X-rayPolarimetry Explorer (IXPE) offer new ways of probing high-energy emissionprocesses in astrophysical jets from blazars. Here we report on the first X-raypolarization observation of the blazar S4 0954+65 in a high optical and X-raystate. During our multi-wavelength campaign on the source, we detected anoptical flare whose peak coincided with the peak of an X-ray flare. Thisoptical-X-ray flare most likely took place in a feature moving along theparsec-scale jet, imaged at 43 GHz by the Very Long Baseline Array. The 43 GHzpolarization angle of the moving component underwent a rotation near the timeof the flare. In the optical band, prior to the IXPE observation, we measuredthe polarization angle to be aligned with the jet axis. In contrast, during theoptical flare the optical polarization angle was perpendicular to the jet axis;after the flare, it reverted to being parallel to the jet axis. Due to thesmooth behavior of the optical polarization angle during the flare, we favorshocks as the main acceleration mechanism. We also infer that the ambientmagnetic field lines in the jet were parallel to the jet position angle. Theaverage degree of optical polarization during the IXPE observation was(14.3$\pm$4.1)%. Despite the flare, we only detected an upper limit of 14% (at3$\sigma$ level) on the X-ray polarization degree; although a reasonableassumption on the X-ray polarization angle results in an upper limit of 8.8%($3\sigma$). We model the spectral energy distribution (SED) and spectralpolarization distribution (SPD) of S4 0954+65 with leptonic (synchrotronself-Compton) and hadronic (proton and pair synchrotron) models. Theconstraints we obtain with our combined multi-wavelength polarizationobservations and SED modeling tentatively disfavor hadronic models for theX-ray emission in S4 0954+65.