Contemporaneous X-ray and Optical Polarization of EHSP Blazar H 1426+428

We present the first contemporaneous X-ray and optical polarimetric measurement of the extremely high synchrotron peaked (EHSP) blazar H 1426+428. The X-ray polarimetric observations were undertaken using the Imaging X-ray Polarimetry Explorer ($\mathit{\text{IXPE}}$) on 2024 May 27, and 2024 July 5. The $\mathit{\text{IXPE}}$ pointings were accompanied by contemporaneous optical observations of the Observatorio de Sierra Nevada, Calar Alto Observatory and the Perkins Telescope Observatory. While we observed the X-ray degree of polarization to be $>20\mathrm{\%}$, the polarization in the optical band was found to be only $1-3\mathrm{\%}$. This trend has been observed in several HSP blazars with available optical and X-ray polarimetric data and is typically explained in terms of energy stratification downstream of a shock. However, we observed a significant difference between the optical and X-ray polarization angles, a feature that has been observed in certain HSP blazars, such as Mrk 421, but remains a relatively rare or underreported phenomenon. We discuss possible scenarios for these findings within the framework of a partially turbulent jet model.