Overview

• IXPE measured a 9.1% X-ray polarization degree in IGR J17091-3624, far exceeding predictions from standard corona geometries.
• The observation undermines the notion that such strong polarization requires a strictly edge-on view of a static corona.
• Simulations indicate the signal can be reproduced by Compton scattering in a rare accretion-disk wind or by a relativistic coronal outflow moving at about 20% of light speed.
• This finding highlights X-ray polarimetry as a powerful diagnostic of plasma dynamics and geometry in the immediate vicinity of black holes.
• Researchers led by Melissa Ewing are refining models and planning additional IXPE observations to discriminate between the wind and outflow explanations.