The Parkes Pulsar Timing Array project

My main research is for the Parkes Pulsar Timing Array (PPTA) project. Our web site provides full information about this project. In brief, we are using the Parkes radio telescope to observe 20 millisecond pulsars. A careful analysis of these observations should allow us to 1) study the existence of low-frequency gravitational waves, 2) look for irregularities in the terrestrial time standard and 3) improve the solar system ephemeris. The PPTA project is a collaboration between the ATNF, UTB, Swinburne and the NAOC. To date, I have been involved in:

• Developing the ATNF digital filterbank system
• Creating the pulsar timing software TEMPO2 (Hobbs, Edwards & Manchester 2006; Edwards, Hobbs & Manchester 2006)
• Creating an improved solar wind electron-density model for pulsar timing (You, Hobbs, Coles, Manchester & Han, in press)
• Studying the effect of dispersion measure variations on pulsar timing (You, Hobbs et al. 2007)
• Calculating an upper bound on the low-frequency stochastic gravitational wave background using pulsar observations (Jenet, Hobbs et al., 2006)
• Describing a technique for detecting a gravitational wave background using pulsar observations (Jenet, Hobbs et al., 2005)
• Removing RFI using adaptive filters (Kesteven, Hobbs et al., 2005)

I am currently working on simulating gravitational wave signals using tempo2, producing a statistically rigorous limit on the gravitational wave background in the presence of red noise and developing methods that will be used to search for correlations in our data sets.

Pulsar timing

I am extremely interested in the timing of large samples of pulsars. The Jodrell Bank Observatory data archive contains observations of many hundreds of pulsars with data spanning up to 35 years. These observations are ideal for studying the long-term stability of pulsars, the interior superfluid, precession and can be used to search for extra-solar planets, obtain accurate proper motions and to study the interstellar medium. The Parkes, Arecibo and GreenBank telescopes provide extremely precise timing observations of a smaller sample of pulsars. These observations can be used for tests of general relativity and looking for pulse shape variations. I have also been involved in long-term timing programs using the Chinese Nanshan radio telescope. So far I have

• Obtained updated timing ephemerides for 374 pulsars (Hobbs, Lyne, Kramer, Martin & Jordan 2004)
• Undertaken a statistical study of 233 pulsar proper motions (Hobbs, Lorimer, Lyne & Kramer, 2005)
• Studied the proper motion, age and initial spin period of PSR J0538+2817 in S147 (Kramer, Lyne, Hobbs, Lohmer, Carr, Jordan & Wolszczan)
• Produced the most stringent tests of general relativity in the strong field regime (Kramer et al. 2006)
• Timing of the relativistic double neutron star system PSR J1756-2251 (Faulkner et al. 2005)
• Timing the young, highly relativistic binary pulsar J1906+0746 (Lorimer et al. 2006)
• Studying a very large glitch event in PSR J1806-2125 (Hobbs et al. 2002)
• Timing measurements of 74 pulsars using the Nanshan telescope (Zou, Hobbs et al. 2005)

Currently I am preparing a paper on the long-term timing stability of 350 pulsars observed at Jodrell Bank.

General pulsar properties

Publications on general pulsar properties have included

• The Australia Telescope National Facility pulsar catalogue (Manchester, Hobbs, Teoh & Hobbs, 2005)
• Evidence for alignment of the rotation and velocity vectors in pulsars (Johnston, Hobbs et al. 2005)
• Evidence for alignment of the rotation and velocity vectors in pulsars II. Further data and emission heights (Johnston et al. 2007)
• PSR J1016-5857: A Young radio pulsar with possible supernova remnant, X-ray and gamma-ray associations (Camilo et al. 2001)
• Pulsar birthrates (Vranesevic et al. 2004)
• The mean pulse profile of PSR J0737-3039A (Manchester et al. 2005)
• Long-term variations in the pulse emission from PSR J0737-3039B (Burgay et al. 2005)
• Implications for binary evolution and equivalence principles with the discovery of three wide-orbit binary pulsars (Stairs et al. 2005)

Pulsar surveys

I was involved in the successful Parkes multibeam pulsar survey and have been part of various other smaller Parkes surveys.

• The Parkes Multibeam Pulsar Survey - VI Galactic population analysis (Lorimer et al. 2006)
• The Parkes Multibeam Pulsar Survey - V Finding binary and millisecond pulsars (Faulkner et al. 2004)
• The Parkes Multibeam Pulsar Survey - IV Discovery of 180 pulsars and parameters for 281 previously known pulsars (Hobbs et al. 2004)
• The Parkes Multibeam Pulsar Survey - III Young pulsars (Kramer et al. 2003)
• The Parkes Multibeam Pulsar Survey -II Discovery and timing of 120 pulsars (Morris, Hobbs et al. 2002)
• Transient radio bursts from rotating neutron stars (McLaughlin et al. 2006)
• Supernova remnants in the Magellanic Clouds (Williams et al. 2005)

Stellar pulsars

Recently various stars (brown dwarfs, MCP stars ...) have been observed to produce periodic pulses of radiation. These objects are not well studied, but have some similar properties to pulsars. We are attempting to develop our understanding of these unusual sources by carrying out long-term monitoring of these stars.

Discovery of pulsars in continuum surveys

Pulsars are typically discovered using FFT-based searches. A few pulsars have been discovered as point sources in continuum surveys. We are developing new techniques to find more pulsars in such data sets.