Author Cackett, Edward M.
Supervisor Horne, K. Metadata Show full item record. Abstract In this thesis I study the inner-most regions of Active Galactic Nuclei AGN using the reverberation mapping technique, and neutron star low-mass X-ray binaries in quiescence using X-ray observations. Time-delays between the continuum at different wavelengths in AGN can be used to probe the accretion disc.
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Here, continuum time-delays in a sample of 14 AGN were used to measure the radial temperature profile of the accretion discs, determine the nuclear extinction, and measure distances to the objects. The implications of this on the thermal disc reprocessing model are discussed. I present two Chandra observations of the neutron star transient in the globular cluster NGC in quiescence, where the power-law component to the spectrum is seen to be variable between the observations, suggesting that there is ongoing residual accretion.
From a Chandra observation of the globular cluster Terzan 1, I have identifed the likely quiescent counterpart to a transient previously observed in outburst, and discuss the other sources within the cluster.
Wind accretion onto compact objects
The defining feature of a black hole is the event horizon. Precise measurements of the black hole shadow would confirm one of the most basic predictions of general relativity and allow one to test and constrain numerous alternative theories of gravity.
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Comparing the data with detailed numerical magneto- hydrodynamic simulations of accretion flows and jets, taking general relativistic light bending and radiation transport into account, also allows testing models of black hole astrophysics in unprecedented detail. Accretion disks and jets are two types of gas flows that have a fundamental impact on the evolution of single and binary stars, the growth of supermassive black holes including possible feedback to their host galaxies , the acceleration of high-energy cosmic rays and the observational signatures of extreme events such as X-ray transients and gravitational-wave mergers.
The fundamental physics of accretion is still poorly understood. Concerning accretion, research questions addressed by the Department are:.
Jets are highly collimated outflows emanating from the vicinity of an accreting central source, invariably rooted in the inner region of an accretion disk:. To answer these questions use is made of theory, numerical modelling 3D magneto-hydrodynamic simulation, including radiation , fast timing optical, X-rays , radio emission and submm-VLBI observations with BlackHoleCam, gravitational wave detections, synoptic surveys and near-infrared imaging and spectroscopy.
Bram Achterberg. Heino Falcke. Paul Groot. Peter Jonker.
Lecture 6 : Accretion disks
Marc Klein Wolt. Jan Kuijpers.
- Luminous disks: How black holes light up their surroundings — Einstein Online;
- Background: Accretion and Jet Production?
- Accretion disks and jets.
- Compact objects in active galactic nuclei and X-ray binaries.
Related The Physics of Accretion onto Compact Objects
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