Accreting neutron stars and black holes in low-mass X-ray binaries are prime laboratories for probing gravity, dense matter, and plasma physics through fast variability. This Special Session will showcase recent breakthroughs in fast X-ray timing, from millisecond pulsations, burst oscillations and high/low-frequency QPOs to phase-resolved spectroscopy, while explicitly linking these diagnostics to multi-wavelength tracers of the accretion-ejection cycle (optical/IR, radio) and, where relevant, multi-messenger constraints. We aim to: (1) assess the state of the field in the NICER, AstroSAT, NuSTAR, XMM-Newton, Insight-HXMT and Einstein Probe era; (2) map timing observables to physical models of the inner flow, boundary layers and coronae; (3) quantify the coupling between variability and jets/winds; (4) highlight synergies with IXPE spectro-polarimetry; and (5) identify analysis standards and high-priority targets for upcoming facilities and coordinated campaigns. The session is designed to bring together observers and theorists across bands, with a strong emphasis on early-career participation and diversity of perspectives, and to produce a concrete list of open problems and community actions for 2026-2028.

Programme

• Fast X-ray timing phenomenology and mission-era highlights
• Fast pulsators and thermonuclear burst physics
• QPOs and inner-flow physics: boundary layers, coronae, and modelling/inference
• Accretion?ejection coupling and synergies: optical/IR and radio timing, winds, IXPE, coordinated campaigns

Invited speakers

Scientific organisers

Andrea Sanna (Chair) (Università degli Studi di Cagliari, Italy), Sudip Bhattacharyya (TIFR- Mumbai, India), Mariano Mèndez (Kapteyn Institute - University of Groningen, Netherlands), Tiziana Di Salvo (Università degli Studi di Palermo, Italy), Sara Motta (INAF - Italy), Alessio Marino (ICE-CSIC, Spain), Matthew Kerr (USN NRL Washington, USA), Alexandra Tetarenko (University of Lethbridge - Alberta - Canada), Poshak Gandhi (University of Southampton, United Kingdom), Duncan Galloway (Monash University, Australia)

Contact

Andrea Sanna: andrea.sanna @ dsf.unica.it