Polarized blazar X-rays imply particle acceleration in shocks

Area of Science:

• Astrophysics
• High-energy astrophysics
• Plasma physics

Background:

• Blazars are active galactic nuclei with jets emitting light produced by high-energy particles (up to 1 TeV).
• The mechanism of particle acceleration in blazar jets, powered by supermassive black holes, remains largely unknown.
• Previous polarization measurements (radio to optical) probed distant regions, not the particle acceleration site.

Purpose of the Study:

• To investigate the particle acceleration mechanism in blazar jets by measuring X-ray polarization.
• To explore the role of magnetic fields in high-energy particle acceleration.
• To probe the conditions closer to the particle acceleration site within the jet.

Main Methods:

• Detection of X-ray polarization from the blazar Markarian 501 (Mrk 501).
• Measurement of the X-ray linear polarization degree (Π_X) and polarization angle.
• Comparison of X-ray polarization measurements with existing optical and radio polarization data.

Main Results:

• Detection of significant X-ray linear polarization (Π_X ≈ 10%) from Mrk 501.
• Measured X-ray polarization degree is approximately double the value observed at optical wavelengths.
• X-ray polarization angle is found to be parallel to the radio jet direction.

Conclusions:

• The results strongly suggest that shock fronts within the blazar jet are the primary sites of particle acceleration.
• The increasing polarization with wavelength implies increasing plasma turbulence with distance from the shock.
• X-ray polarization measurements provide a direct probe of the particle acceleration process in blazar jets.