X-MAPS

X-MAPS (X-ray Measurements of Accreting black holes with Polarimetric-Spectral-timing techniques) is my ERC Consolidator Grant project. The project aims to unify spectral, polarimetry and fast timing techniques to uncover the accretion geometry of X-ray binaries during state transitions and measure black hole mass and spin. This page will contain information about the project, including job opportunities, the X-MAPS team, and research outputs.

X-MAPS Summary

Black hole (BH) X-ray binaries (XRBs) radiate a huge X-ray flux from the BH vicinity. The X-ray signal, radiated by a hot corona and a cooler disk, contains information on the BH mass and spin, and the strong gravitational field close to its horizon. However, the X-ray emitting region is unresolvable, necessitating indirect mapping techniques. My group has recently made strong progress using forward-modelling spectral-timing techniques that exploit rapid spectral variability, and the recent launch of the Imaging X-ray Polarimetry Explorer (IXPE) has enabled the first studies of X-ray polarization. X-MAPS will take the novel and transformational step of combining these two powerful diagnostics into polarimetric-spectral-timing. This requires a huge increase in the computational intensity of our state-of-the-art models, that we will enable with machine learning to achieve the following science goals:
1) Understand state transitions: We will constrain how the structure of the disk-corona system evolves as the spectral shape changes and large-scale transient jets are launched, informing on the jet launching mechanism and thus how supermassive BHs influence their host galaxies.
2) Measure BH mass: The current observational picture that BHs in gravitational wave (GW) sources are heavier than those in Galactic XRBs has deep implications for binary evolution theory. We will make BH mass measurements using the X-ray signal alone, enabling measurements for XRBs inaccessible to traditional optical techniques (~70% of the population), which are thought to harbour heavier BHs. This will enable us to test the importance of observational bias in the comparison of XRBs with GW sources.
3) Measure 3D BH spin orientation: The advent of X-ray polarimetry enables a novel test to determine whether or not the quasi-periodic oscillations (QPOs) we observe in the X-ray flux of XRBs are driven by relativistic precession of the corona around the BH spin axis: searching for variation of X-ray polarization with QPO phase. We will test this model prediction and, if confirmed, will reconstruct the precession cone and thus the BH spin vector, providing new insights into binary evolution theory.