Kavli Affiliate: Nicola Omodei
| First 5 Authors: W. Peter Maksym, Ioannis Liodakis, M. Lynne Saade, Dawoon E. Kim, Riccardo Middei
| Summary:
X-ray polarization is a unique new probe of the particle acceleration in
astrophysical jets made possible through the Imaging X-ray Polarimetry
Explorer. Here we report on the first dense X-ray polarization monitoring
campaign on the blazar Mrk 421. Our observations were accompanied by an even
denser radio and optical polarization campaign. We find significant
short-timescale variability in both X-ray polarization degree and angle,
including a $sim90^circ$ angle rotation about the jet axis. We attribute this
to random variations of the magnetic field, consistent with the presence of
turbulence but also unlikely to be explained by turbulence alone. At the same
time, the degree of lower-energy polarization is significantly lower and shows
no more than mild variability. Our campaign provides further evidence for a
scenario in which energy-stratified shock-acceleration of relativistic
electrons, combined with a turbulent magnetic field, is responsible for optical
to X-ray synchrotron emission in blazar jets.
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