Shedding new light on the Crab with polarized X-rays

Area of Science:

• Astrophysics and Astronomy
• High-Energy Astrophysics
• Polarimetry

Background:

• Compact celestial X-ray sources exhibit strong magnetic fields, synchrotron emission, and Compton scattering.
• X-ray emissions from these sources are expected to be linearly polarized.
• X-ray polarimetry is crucial for understanding emission mechanisms and locations.

Purpose of the Study:

• To measure the hard X-ray polarization of the Crab nebula for the first time.
• To investigate the emission site and mechanisms in the Crab nebula using polarization data.
• To compare hard X-ray polarization with optical observations.

Main Methods:

• Utilized a purpose-built and calibrated polarimeter, PoGO+.
• Measured polarization in the hard X-ray band (~20-160 keV).
• Analyzed polarization parameters of the Crab nebula and its pulsar.

Main Results:

• The hard X-ray polarization vector is aligned with the pulsar's spin axis.
• A polarization fraction of (20.9 ± 5.0)% was measured, higher than the optical diffuse nebula.
• No significant temporal evolution of phase-integrated polarization parameters was observed.

Conclusions:

• The results suggest a more compact emission site in the hard X-ray band compared to the optical diffuse nebula.
• First-time measurement of X-ray polarization parameters for the pulsar itself are consistent with optical observations.
• Hard X-ray polarimetry offers unique insights into the physics of the Crab nebula.