X-ray Binaries
Master
Site: Merate (LC)
Duration:
1 year (master)
Tutor
Maria Cristina Baglio
Contact
maria.baglio AT inaf.it
Description
CONTEXT – X-ray binaries (systems in which a black hole or neutron star accretes matter from a companion star) undergo outbursts, dramatic increases in luminosity caused by instabilities in the accretion disc. As the outburst evolves, the accretion flow changes structure: in some phases, the inner disc recedes and is replaced by a hot, optically thin, radiatively inefficient flow; in others, the system launches relativistic jets. Both the hot flow and jets produce synchrotron emission, which may contribute to the system’s optical polarization. At the same time, thermal components such as the outer disc can also introduce polarization through scattering. Studying how polarization evolves across different phases provides a unique window into the geometry and physical conditions of these emission regions.
PROPOSED WORK – This thesis will analyze multi-epoch optical polarimetric data acquired with the Very Large Telescope (VLT) for one black hole or neutron star X-ray binaries. Optical and near-infrared photometry from the LCO network and REM telescopes will complement the polarization data, tracing changes in spectral energy distribution and total flux across outburst phases.
The project aims to disentangle the origins of optical polarization, whether from synchrotron emission in jets or hot flows, or from Thomson scattering in the outer accretion disc, and to study how these contributions evolve. Where available, simultaneous radio observations will provide direct insight into jet activity, enabling a full multiwavelength view of inflow–outflow coupling.
This work will help constrain the geometry and physical evolution of accreting systems during outburst, with implications for jet formation and accretion physics.
[Credit image: WEB]
