Detection of X-ray Polarization from the Blazar 1ES 1959+650 with the Imaging X-ray Polarimetry Explorer

Kavli Affiliate: Grzegorz Madejski

| First 5 Authors: Manel Errando, Ioannis Liodakis, Alan P. Marscher, Herman L. Marshall, Riccardo Middei

| Summary:

Observations of linear polarization in the 2-8 keV energy range with the
Imaging X-ray Polarimetry Explorer (IXPE) explore the magnetic field geometry
and dynamics of the regions generating non-thermal radiation in relativistic
jets of blazars. These jets, particularly in blazars whose spectral energy
distribution peaks at X-ray energies, emit X-rays via synchrotron radiation
from high-energy particles within the jet. IXPE observations of the X-ray
selected BL Lac-type blazar 1ES 1959+650 in 2022 May 3-4 showed a significant
linear polarization degree of $Pi_mathrm{x} = 8.0% pm 2.3%$ at an
electric-vector position angle $psi_mathrm{x} = 123^circ pm 8^circ$.
However, in 2022 June 9-12, only an upper limit of $Pi_mathrm{x} leq 5.1%$
could be derived (at the 99% confidence level). The degree of optical
polarization at that time $Pi_mathrm{O} sim 5%$ is comparable to the X-ray
measurement. We investigate possible scenarios for these findings, including
temporal and geometrical depolarization effects. Unlike some other X-ray
selected BL Lac objects, there is no significant chromatic dependence of the
measured polarization in 1ES 1959+650, and its low X-ray polarization may be
attributed to turbulence in the jet flow with dynamical timescales shorter than
1 day.

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