Speaker
Description
Low-mass X-ray binaries are perfect laboratories for studying accretion physics and its coupling with jets and outflows. The advent of X-ray polarimetry with IXPE has opened a new window onto the geometry of the innermost accretion regions, yet a complete physical picture demands a broader, multi-wavelength perspective.
I will show how optical polarimetry provides an important complementary view, tracing emission from the accretion disc, jets, and disc winds on scales inaccessible to X-ray instruments alone. I will present case studies illustrating the diagnostic power of this approach. In GX 339−4, simultaneous IXPE and VLT/FORS2 observations reveal X-ray and optical polarisation angles both aligned with the resolved jet axis, pointing to a corona horizontally extended in the disc plane. In Swift J1727.8−1613, dense optical monitoring uncovers a polarisation change coincident with discrete radio ejections, with an intrinsic angle offset from the jet, interpreted as spin–orbit misalignment and scattering in a disc wind. In IGR J17091−3624, an exceptionally high X-ray and optical polarisation degree with consistent angle favour disc wind scattering. Finally, preliminary results from GS 1354-64 reveal optical polarisation angle variations across the outburst which reflect changes in the dominant emission component or disc geometry.
These results show that combining optical and X-ray polarimetry with broadband spectral modelling allows us to simultaneously constrain accretion geometry, jet and wind launching conditions, and their complex interplay.