High Energy Astrophysics at Southampton

Lead Research Organisation: University of Southampton
Department Name: School of Physics and Astronomy


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.

Planned Impact

The Astronomy Group has achieved significant impact in both its outreach activities and in knowledge exchange. The School's outreach work reaches a large number of people (typically 9000 per year), in which astronomy plays a central role. While these activities have traditionally focussed on the general public and students, more recently there have been targetted opportunities to give support to teachers, such as the School's partnership with the local Science Learning Centre. Thus we have been able to provide input and support to the teachers which can have much longer-term value for their future teaching of basic scientific principles. Our outreach activities, including teacher support, is enhanced through the new Winchester Science Centre and Planetarium, in which the Astronomy Group plays a significant role. There have also been many opportunities for Astronomy Group members to participate in science open days, fairs and cafes, interest in which has exploded following the highly successful International Year of Astronomy in 2009.

Exploiting astronomy research in completely different environments and communities has always been important in the Astronomy Group whenever
appropriate circumstances arise, and our work has recently provided two examples of such knowledge exchange. Both were related to the
mathematical techniques that had to be developed in order to model the rapid variability observed in X-ray binaries and AGN. The techniques
themselves were of interest to the University's own Complexity Group, whilst the students involved in developing the techniques for their
theses obtained positions in the financial world where these techniques have the potential to be applied to the variability of stocks and shares. Furthermore, the Astronomy Group's years of developing satellite hardware led to the creation of Symetrica, a now highly successful spin-off company in the international security market, who have in turn funded PhD studentships and participate in supporting our undergraduate projects.


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Harwood J (2015) Spectral ageing in the lobes of cluster-centre FR II radio galaxies in Monthly Notices of the Royal Astronomical Society

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Heesen V (2015) The non-thermal superbubble in IC 10: the generation of cosmic ray electrons caught in the act in Monthly Notices of the Royal Astronomical Society: Letters

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Hardcastle M (2015) Deep Chandra observations of Pictor A in Monthly Notices of the Royal Astronomical Society

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Description This grant comprised of allocations to 3 separate research areas: Disc-jet coupling (Fender), AGN feedback in groups and clusters (Croston) and AGN variability (McHardy). In Disc-Jet coupling a major discovery of the ubiquity of winds from the accretion discs in soft state X-ray binary systems was made. Also a new track was found in the relationship between X-ray and radio luminosities of X-ray binaries, casting doubt on the assumption that only one mode of emission (inefficient) occurred in hard state X-ray binary systems. In AGN feedback, questions have been posed regarding the validity of our understanding of radio relics by the observation (in X-rays) of shocks with very different velocities to those expected on the basis of the radio observations. In AGN variability we published the first major General Relativistic modelling survey of Fourier-resolved X-ray lags in AGN. We were able to measure black hole masses, black hole spin and the size of the X-ray source. Also, we made the first detailed study of the size of AGN accretion discs by careful measurement of the lags between the X-ray, UV and optical wavebands. We found the discs to be three times larger than expected based on the standard theoretical model for accretion discs which all astronomers have relied on for over 40 years.
Exploitation Route Others will wish to investigate further the results mentioned above. Eg large observational programmes are now being carried out using the NASA Swift X-ray observatory to measure X-ray/UV/optical lags in more AGN.
Sectors Education,Leisure Activities, including Sports, Recreation and Tourism,Culture, Heritage, Museums and Collections

URL http://adsabs.harvard.edu/abstract_service.html