High-mass X-ray binaries (HMXBs) represent a critical phase in the evolutionary history of massive binary systems. Recent detections of mergers between compact objects, such as the 2017 observation of two neutron stars merging, have renewed interest in HMXBs, as these systems are believed to be potential progenitors of such events. In HMXBs, a compact stellar remnant, typically a highly magnetised neutron star (NS), orbits a massive star, accreting material from the stellar wind of a blue supergiant or the decretion disk of a quickly spinning Be star. This accretion process influences the neutron star's spin, causing it to either speed up or slow down, depending on the interaction between the accreted plasma and the extended NS magnetosphere.
Despite decades of observations, the behaviour of accretion-powered pulsars in HMXBs remains puzzling. Many NSs in these systems exhibit slow rotation and erratic spin changes, including sudden torque reversals whose origins remain unclear. Surprisingly, the expected correlation between the NS spin evolution and X-ray luminosity is absent, indicating a gap in our understanding of how the accreted material couples to the NS magnetic field and magnetosphere.
The motivation for this workshop arises from recent advancements in both observations and simulations of mass transfer in HMXBs. New insights from simulations show that the captured material in HMXBs can form a disk-like structure around the NS, challenging previous assumptions about the accretion process. Additionally, recent X-ray timing analyses have revealed significant, previously unnoticed variations in the NS spin on short timescales, further complicating our understanding of the accretion process.
This workshop brings together experts in observational and theoretical studies of accreting pulsars to develop a more comprehensive model of accretion-induced torques in NS-hosting HMXBs. Key objectives include analysing archival and new data to understand the torques at play, developing new models to predict their behaviour, and designing numerical simulations to study the coupling between the accreted material and the NS magnetosphere. By integrating expertise in pulsar timing, X-ray spectroscopy, and magnetospheric physics, the workshop aims to bridge the gap between observations and theory in this complex field.
SOC
- Ileyk El Mellah (Universidad de Santiago de Chile, CIRAS).
- Alicia Rouco Escorial (ESAC/ESA)
- Christian Malacaria (INAF/Osservatorio Astronomico di Roma)
- Silvia Martínez-Núñez (IFCA (CSIC-UC))
- Raphaël Mignon-Risse (Norwegian University of Science and Technology)
- Georgios Mountrichas (IFCA (CSIC-UC))
Sponsors
Esta actividad es posible gracias a la financiación de la Consejería de Educación, Formación profesional y Universidades del Gobierno de Cantabria (Protocolo General del Contrato-Programa Gobierno de Cantabria-UC), a través del Proyecto: “Actividad estructural para el desarrollo de la investigación del Instituto de Física de Cantabria''.