Astronomers from Wales and the Netherlands, in collaboration with five schools, have used eight telescopes simultaneously to study the strange behaviour of an X-ray binary star system. Results will be presented by postgraduate student Fraser Lewis at the RAS National Astronomy Meeting in Llandudno, Wales, on Monday 18th April.
IGR J00291+5934 (‘00291’) is a rare X-ray binary system containing a pulsar – a neutron star spinning several hundred times per second – and a normal star. Only 12 such systems are known. In September 2008, 00291 increased in brightness at X-ray wavelengths by a factor of at least a thousand times and in visible wavelengths by a factor of around a hundred times. While this type of outburst is not uncommon for this type of system, the timescale is usually months to years. However 00291, having been in outburst for 20 days, faded away to its normal faint state but then re-brightened within 30 days.
"We had never seen this rapid a turnaround in a system of this type before" said Lewis, of the Faulkes Telescope Project at the University of Glamorgan. "To try to understand what was driving this unique behaviour, we gathered data from several telescopes, at different wavelengths, to create a dataset of unprecedented detail."
The group, led by Lewis and Dr David Russell, of the University of Amsterdam, used data from Faulkes Telescope North, the Isaac Newton Telescope and the Keck Telescope (optical wavelengths), PAIRITEL (infrared), the Westerbork Synthesis Radio Telescope (radio), the Swift GRB mission (UV and X-ray), and the XMM-Newton and RXTE satellites (X-ray). Five schools, including St. Brigid's School, Denbigh and St Davids College, Cardiff, were involved in collecting the data using Faulkes Telescope North.
In X-ray binary systems, material from the star spirals in towards the pulsar, forming an accretion disc. Friction and gravity heat this material up until it reaches temperature of millions of degrees and emits X-rays.
"The behaviour of 00291 is baffling. Outbursts are thought to be driven by the 'emptying' of the accretion disc, which means that the time between outbursts indicates the time that it takes to fill the disc, and the size of the disc itself. However, for a system as compact as 00291, it’s unlikely that it could replenish its supply within 30 days," said Lewis.
To find a solution to this mystery, Lewis and Russell have turned to a group at the Naval Research Laboratory in Washington led by Dr Jacob Hartman. Hartman's group suggests that the outburst is all one event that was interrupted halfway through by a propeller effect.
"The idea is that when the 'propeller' switches on, the material that was spiralling inwards becomes ejected from the system, stopping the outburst. Then the propeller switches off again, the outburst restores itself. However, there are still many things that we don’t understand," said Lewis.
"My pupils always love using the FT, in particular they are inspired by the real-time nature of the experience and awed by the idea that they see exactly what the telescope sees, so many miles away, staring deep into space at impossibly distant and mysterious objects. What was especially exciting about our session with IGR J00291+5934 was that a few months later we saw our name in a paper proving that we had contributed to some proper science. This thrilled the children no end and who knows what sparks were kindled by this experience?" said Stuart Ayres, a teacher from St. Brigid's School, Denbigh.
These results are presented within the wider context of an extensive optical monitoring program of 32 low-mass X-ray binaries using the 2-metre Faulkes Telescopes in Hawaii and Australia.
Faulkes Telescope Project
University of Glamorgan
Fraser Lewis is contactable through the NAM2011 Press Office on Monday 18th April.
NAM 2011 Press Office (0900 – 1730 BST, 18-21 April only)
Venue Cymru conference centre
Tel: +44 (0)1492 873 637, +44 (0)1492 873 638
Dr Robert Massey
Royal Astronomical Society
Mob: +44 (0)794 124 8035
Royal Astronomical Society
Mob: +44 (0)7756 034 243
'The double-peaked 2008 outburst of the accreting milli-second X-ray pulsar, IGR J00291+5934*' (Fraser Lewis et al, 2010, Astronomy & Astrophysics, Volume 517, A72)
'A Double Outburst from IGR J00291+5934: Implications for Accretion Disk Instability Theory' (Jacob M Hartman et al, 2011, ApJ, 726, p.26).
For artist’s impression of IGR J00291+5934, see: http://www.esa.int/esaCP/SEMWSAA5QCE_index_1.html
NOTES FOR EDITORS
Bringing together around 500 astronomers and space scientists, the RAS National Astronomy Meeting 2011 (NAM 2011: http://www.ras.org.uk/nam-2011) will take place from 17-21 April in Venue Cymru (http://www.venuecymru.co.uk), Llandudno, Wales. The conference is held in conjunction with the UK Solar Physics (UKSP: http://www.uksolphys.org) and Magnetosphere Ionosphere and Solar-Terrestrial Physics (MIST: http://www.mist.ac.uk) meetings. NAM 2011 is principally sponsored by the RAS and the Science and Technology Facilities Council (STFC: http://www.stfc.ac.uk).
The Royal Astronomical Society
The Royal Astronomical Society (RAS: http://www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3500 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.
The Science and Technology Facilities Council
The Science and Technology Facilities Council (STFC: http://www.stfc.ac.uk) ensures the UK retains its leading place on the world stage by delivering world-class science; accessing and hosting international facilities; developing innovative technologies; and increasing the socio-economic impact of its research through effective knowledge exchange. The Council has a broad science portfolio including Astronomy, Particle Astrophysics and Space Science. In the area of astronomy it funds the UK membership of international bodies such as the European Southern Observatory.
Venue Cymru (http://www.venuecymru.co.uk) is a purpose built conference centre and theatre with modern facilities for up to 2000 delegates. Located on the Llandudno promenade with stunning sea and mountain views; Venue Cymru comprises a stunning location, outstanding quality and exceptional value: the perfect conference package.
The Faulkes Telescope Project
The Faulkes Telescope Project is an educational and research project, based at the University of Glamorgan and funded by the Dill Faulkes Educational Trust. The telescopes are maintained by Las Cumbres Observatory Global Telescope (LCOGT), based in Goleta, California. The schools involved were St. Brigid's School (Denbigh), St. David’s College (Cardiff), Paulet High School (Burton-on-Trent), The Kingsley School (Leamington Spa) and Czacki High School (Warsaw, Poland).