High Energy Astrophysics at Southampton (Cons Grant)

Our research concerns compact objects, ie white dwarfs, neutron stars and black holes (BHs), both stellar sized and supermassive (SMBHs). We aim to understand how they evolve and how they produce radiation. X-ray binaries (XRBs), which contain bright accretion discs around BHs and neutron stars, allow detailed examination of how these discs vary. As they vary quickly, many measurements of variability can be made, allowing us to see how variability at different frequencies is tied together. Using these measurements, we can test fundamental ideas about how and why matter falls in through discs. Using variations in the infrared emission, we can look at variations in the jet, and learn how the discs feed the relativistic jets we see in XRBs. Strong radio emission from the jet often accompanies accretion, particularly in the `hard' state of XRBs. We will investigate how radio emission, as seen in new observatories such as LOFAR and eMERLIN, is related to X-ray emission, as a means of studying the accretion/outflow connection. We will study why, in hard state sources, the potential accretion energy is sometimes converted efficiently into radiation, and sometimes not. We will measure black hole spin, which is important in determining how much of the accretion energy can be liberated as radiation. Studying massive stars in binary systems and their evolution gives important insight into recent star formation in the Milky Way and nearby galaxies. The evolved stellar population of the SMC points to recent turbulent interactions with its companion galaxy, producing a very active period of star formation. Many of these massive stars have evolved through a supernova phase, producing a large population of neutron stars. Studies of this population are revealing crucial insight into the nature of stellar evolution. Accreting white dwarfs (AWD) are astrophysically important. They include Type Ia Supernova progenitors, and the processes that drive their evolution are relevant in many other settings. Here we will extend our leading work on the evolution of AWDs and related systems. We will implement a new evolution track for AWDs, directly detect the first sub-stellar secondary, determine the space density of AWD, carry out a search for dead AWDs and confirm the first double-degenerate SN Ia progenitor. We will study the relationship between stellar-mass BHs and SMBHs (ie AGN), asking whether properties such as variability timescales, or time lags between energy bands, scale only with mass, or also with accretion rate. We will see whether AGN which have jets vary differently to those which don't, and if X-rays and Gamma-rays vary differently. We will observe how optical and radio variations are related to X-ray variations in AGN with and without jets. Thus, in different AGN types, we will determine how and where the emissions in different wavebands are produced and why they vary. The large-scale jets from SMBHs can extend for distances of millions of light years, transporting energy not only to their host galaxy but also to the surrounding group or cluster of galaxies. This energy input plays an important role in how galaxies and clusters form and evolve. We will use new radio facilities, e.g. LOFAR and e-MERLIN, to measure the energetic impact of, and investigate the life cycles of, different populations of radio-loud AGN, to understand their role in galaxy evolution. SMBHs exist in the nuclei of possibly all galaxies but are often undetectable due to very low accretion rates. To study these low luminosity AGN, which dominate the local universe, we are making a sensitive radio and X-ray survey of the best-selected sample of nearby galaxies, the Palomar sample, to find faint AGN and determine which host galaxy properties (eg mass, starformation rate) most strongly control AGN luminosity. We will also perform the cleanest measurement yet of how radio emission, X-ray emission and BH mass are related.