The high polarisation of the X-rays from the Black Hole X-ray Binary 4U 1630-47 challenges standard thin accretion disc scenario
Large, energy-dependent X-ray polarisation is observed in 4U 1630-47, a black hole in an X-ray binary, in the high-soft emission state. In this state, X-ray emission is believed to be dominated by a thermal, geometrically thin, optically thick accretion disc. However, the observations with the Imaging X-ray Polarimetry Explorer (IXPE) reveal an unexpectedly high polarisation degree, rising from 6% at 2 keV to 10% at 8 keV, which cannot be reconciled with standard models of thin accretion discs. We argue that an accretion disc with an only partially ionised atmosphere flowing away from the disc at mildly relativistic velocities can explain the observations.
- Pub Date:
- April 2023
- Astrophysics - High Energy Astrophysical Phenomena
- Submitted to Nature Astronomy