Detection of X-ray polarization in the high synchrotron peaked blazar 1ES 1959+650

Abstract

We report the measurement of X-ray polarization in the high synchrotron peaked blazar 1ES 1959+650. Of the four epochs of observations from the Imaging X-ray Polarimetry Explorer, we detected polarization in the 2–8 keV band on two epochs. From the model-independent analysis of the observations on 28 October 2022, in the 2–8 keV band, we found the degree of polarization of ΠX=9.0±1.6% and an electric vector position angle of ΨX=53±5 deg. Similarly, from the observations on 14 August 2023, we found ΠX and ψX values as 12.5±0.7% and 20±2 deg, respectively. These values are also in agreement with the values obtained from spectro-polarimetric analysis of the I, Q, and U spectra. The measured X-ray polarization is larger than the reported optical values, ranging between 2.5% and 9% when observed from 2008 to 2018. Broadband spectral energy distribution constructed for the two epochs is well described by the one-zone leptonic emission model with the bulk Lorentz factor (Γ) of the jet larger on 14 August 2023 compared to 28 October 2022. Our results favor the shock acceleration of the particles in the jet, with the difference in ΠX between the two epochs being influenced by a change in the Γ of the jet.