Project description
Mass measurement of black hole X-ray binaries with polarimetric-spectral-timing techniques
When a black hole forms in a binary star system, an enormous X-ray flux radiates around the black hole. This electromagnetic signal, emitted by a hot corona and a cooler disk, carries key information on the black hole’s mass, spin and strong gravitational field close to its horizon. However, the actual X-ray emitting region remains obscure. Using the X-ray signal alone, the ERC-funded X-MAPS project aims to measure the mass of accreting black holes and gain insight into disk-corona state transitions. To do so, it will integrate indirect mapping methods with its own pioneering forward-modelling spectral-timing methods to create novel polarimetric-spectral-timing techniques. The outcomes are expected to have an impact on current binary evolution theories.
Objective
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. I pioneered forward-modelling spectral-timing techniques that exploit rapid spectral variability, and played a key role in 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 my state-of-the-art models that my group 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: I recently found strong evidence that quasi-periodic oscillations (QPOs) observed in the X-ray flux of XRBs are driven by relativistic precession of the corona around the BH spin axis: variation of X-ray polarization with QPO phase. We will reconstruct the precession cone and thus the BH spin vector, providing new insights into binary evolution theory.
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Keywords
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Project’s keywords as indicated by the project coordinator. Not to be confused with the EuroSciVoc taxonomy (Fields of science)
Programme(s)
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Multi-annual funding programmes that define the EU’s priorities for research and innovation.
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HORIZON.1.1 - European Research Council (ERC)
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Call for proposal
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(opens in new window) ERC-2024-COG
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DH1 3LE DURHAM
United Kingdom
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