Swarnim Sashank: X-ray reflection spectroscopy with non-standard accretion geometries

Thursday 27 Aug 2026, 15:00 → 16:00 Europe/Stockholm

A5:1003 (AlbaNova Main Building)

X-ray reflection models are widely used to analyze accreting systems and have achieved considerable success in measuring black hole spins. However, they tend to infer very high spins in X-ray binary systems, raising the question of whether these measurements are affected by systematic biases. A key limitation is that current reflection models rely on simplified analytical assumptions about the accretion geometry. General relativistic magnetohydrodynamic (GRMHD) simulations provide a more realistic description of accretion flows from first principles. I use GRMHD simulations to model X-ray reflection from accreting black hole systems and generate synthetic spectra to test the ability of current reflection models to recover the input parameters after folding the spectra through an instrumental response. I also present a new model, REFLUX, specifically designed to analyze reflection features in super-Eddington systems, where reflection may originate from slim disks or optically thick winds. These simulations reveal systematic uncertainties in current reflection models and highlight the need to incorporate more realistic accretion geometries and richer physics. Such advances will be particularly important for the next generation of X-ray observatories, including eXTP and NewAthena.