Sean Farrell - School of Physical, Environmental and Mathematical Sciences (PEMS)

Every year the Research and Research Training Office awards a limited number of travel grants to postgraduate students. These competitive grants have been established to assist full-time postgraduate research students to travel overseas to conduct activities that are relevant to the completion of their research. Activities may include presenting papers at international conferences, undertaking a research field trip or undertaking collaborative research with other Universities and Research Institutions. Sean Farrell was awarded a UNSW@ADFA Postgraduate
Student Overseas Travel Grant as well as an Astronomical Society of Australia Overseas Travel Grant.

From the 11^th 25^th June 2006 I attended an international astronomy conference in Cefalù, Sicily. The conference theme was The Multicoloured Landscape of Compact Objects and their Explosive Origins which integrated very well with my research into the multi-wavelength behaviour of X-ray binaries. The topics covered were Gamma Ray Bursts, Magnetars, and Supernovae in the first week followed by Neutron Star and White Dwarf Systems (observation vs theory plus correlated temporal and spectral variability), X-ray & Radio Millisecond Pulsars, Secular Evolution of X-ray Binaries, Compact Binaries as Sources of Gravitational Radiation, Accretion onto Black Hole Microquasars & Ultra-luminous X-ray Sources, Interacting Binaries, and Active Galactic Nuclei in the second week. Throughout the conference I presented a poster summarising the major results of my doctoral research, entitled "A Multicoloured View of 2S 0114+650 – an unusual X-ray binary"” (Farrell, O'Neill, Sood, Dieters and Manchanda) which we will submit for publication in the refereed conference proceedings with a possible follow up paper to be submitted later to MNRAS.

I gained a great deal from attending this conference, not least of which was a wonderful cultural experience. I met a number of researchers from around Europe (including from SRON, Oxford University and Open University) who are interested in forming collaborations with our group. One of these potential collaborators has offered to provide 4.5 Million seconds of timing and spectral data on 2S 0114+650 from the INTEGRAL space telescope, which will allow us to constrain the properties of this source to an even higher level. I learnt a lot about the numerous research areas that are closely linked to my own field, giving me a much improved understanding of the field of High Energy Astrophysics. I also raised the profile of my research and in doing so also raised the profile of my institution and that of Australian Astronomy & Astrophysics in general. Finally, the feedback from discussions of my work with the leading researchers in my field was incredibly beneficial and will be incorporated into the final steps of my project and will heavily influence the writing of my thesis.

X-ray binary (XRB) star systems, consisting of a "normal" donor star and a compact object (either a neutron star or black hole), allow us to study the behaviour of matter under extreme gravity such as cannot be studied in any laboratory on Earth. Variations in the X-ray emission from such systems are a signature of high-energy processes and allow an insight into the underlying system dynamics.

While the short-term variability of X-ray binaries has been well studied, the long-term variability (in the range of days to years) is not yet well understood. Many recent X-ray satellite missions such as NASA's Rossi X-ray Timing Explorer (RXTE) have been equipped with All Sky Monitor (ASM) instruments, allowing X-ray sources to be monitored on long time-scales previously unachievable.

Using ~8 years of RXTE ASM data, we have identified long-term variations in the light curves of a number of X-ray binaries, particularly the High Mass X-ray Binary 2S0114+650 and the Black Hole candidate GX339-4. These periodicities or super-orbital periods (so named as they are longer than the known orbital periods) have a number of possible causes, including:

This project aims to further our understanding of the behaviour of X-ray binaries and the mechanisms of accretion through a multi-wavelength study of selected XRB sources.

Dieters, S., O'Neill, P., Farrell, S., Sood, R. (2004). Long -term periodicities in the flux from low mass X-ray binaries, Advances in Space Research

Farrell, S., & Sood, R. (2004). Recurrent ~24 hr periods in RXTE data - an artifact of the satellite's orbit?, PASA

Farrell, S., Sood, R., O'Neill, P. (2004). The super-orbital period of the High Mass X-ray Binary pulsar 2S0114+650, MNRAS (ATEL # 283)