Polarization of the Crab Pulsar and Nebula as Observed by the INTEGRAL/IBIS Telescope

Neutron stars generate powerful winds of relativistic particles that form bright synchrotron nebulae around them. Polarimetry provides a unique insight into the geometry and magnetic configuration of the wind, but high-energy measurements have failed until recently. The INTEGRAL/IBIS telescope has been used in its Compton mode to search for linearly polarized emission for energies above 200 keV from the Crab Nebula. The asymmetries in the instrument response are small and we obtain evidence for a strongly polarized signal at an angle parallel to the pulsar rotation axis. This result confirms the detection recently reported by Dean and coworkers, and extends the polarization measure for all the pulsar’s phases. The hard X-ray/soft γ-ray observations therefore probe the inner jets or equatorial flow of the wind. The achieved sensitivity opens a new window for polarimetric studies at energies above 200 keV.