M. Bailes

Probing the eclipse region of a binary millisecond pulsar

We report the discovery of a new eclipsing millisecond binary pulsar system, PSR J2051-0827. The pulsar has a period of 4.5 ms and is in a very compact circular orbit with a companion of mass ~0.03 M☉. Observations at low frequencies show that the eclipse duration is approximately 10% of the orbital period. However, at high radio frequencies, pulses are often detected throughout the eclipse region, revealing interesting time-variable density structure in the eclipsing plasma.

Mean Pulse Shape and Polarization of PSR J0437–4715

Mean pulse shape and polarization parameters have been obtained for PSR J0437-4715 at 438, 660, and 1512 MHz using the Australia Telescope National Facility Parkes 64 m radio telescope and the Caltech correlator. The pulse profile is complex with many identifiable features, including an unusual double notch, and evolves strongly with frequency. Strong linear and circular polarization are observed at all frequencies, with the fractional linear polarization highest near the wings of the pulse. Circular polarization is strongest near the pulse center, with a sense reversal at the center. Position-angle variations are complex and include what appear to be orthogonal-mode transitions. However, at other frequencies, some of these transitions are not orthogonal. Even when these transitions are allowed for, the position angle does not follow the simple rotating-vector model, suggesting departures from a dipole field configuration in the emission region. A frequency-dependent lag of the total-intensity profile with respect to the polarization profile is observed. This effect has not previously been seen in any pulsar. An improved value of the rotation measure along the path to the pulsar is derived.

Discovery of Four Isolated Millisecond Pulsars

We report the discovery of four isolated millisecond pulsars found as part of the Parkes 436 MHz survey of the southern sky. Three of the pulsars, PSRs J1024-0719, J1744-1134, and J2124-3358, are close to the Sun (d < 360 pc) and have very low luminosities, 0.5 mJy kpc2. The other, PSR J0711-6830, is of intermediate luminosity. The four least luminous millisecond pulsars presently known are all isolated objects, even though more than 75% of the known disk millisecond pulsars are binary. A Kolmogorov-Smirnov analysis confirms that the luminosity distributions of the binary and isolated millisecond pulsars are different at the 99.5% confidence level. We can find no simple explanation for this fact. The low-luminosity millisecond pulsars reported here exacerbate the birthrate discrepancy with their assumed progenitors, the low-mass X-ray binaries. None of the pulsars exhibits any evidence of a planetary system such as that observed around PSR B1257+12, indicating that planetary formation around millisecond pulsars is rare.

The Proper Motion and Parallax of PSR J0437?4715

We report timing results for PSR J0437-4715 obtained using the Australia Telescope National Facilitys Parkes radio telescope and the Caltech correlator. After model fitting, the timing residuals are only ~500 ns, allowing significant measurements of the annual parallax and the secular change in the orientation of the orbit arising from the systems proper motion. These results allow several independent and self-consistent estimates of the pulsars distance, placing it ~30% farther away than the dispersion measure-derived distance. They also place constraints on the mass of the binary companion and the orbital inclination of the system.

Timing models for the long orbital period binary pulsar PSR B1259–63

The pulsar PSR B1259−63 is in a highly eccentric 3.4-yr orbit with the Be star SS 2883. Timing observations of this pulsar, made over a 7-yr period using the Parkes 64-m radio telescope, cover two periastron passages, in 1990 August and 1994 January. The timing data cannot be fitted by the normal pulsar and Keplerian binary parameters. A timing solution including a (non-precessing) Keplerian orbit and timing noise (represented as a polynomial of fifth order in time) provide a satisfactory fit to the data. However, because the Be star probably has a significant quadrupole moment, we prefer to interpret the data by a combination of timing noise, dominated by a cubic phase term, and ω̇ and ẋ terms. We show that the ω̇ and ẋ are likely to be a result of a precessing orbit caused by the quadrupole moment of the tilted companion star. We further rule out a number of possible physical effects which could contribute to the timing data of PSR B1259−63 on a measurable level.

Implications of a VLBI Distance to the Double Pulsar J0737-3039A/B

The double pulsar J0737-3039A/B is a unique system with which to test gravitational theories in the strong-field regime. However, the accuracy of such tests will be limited by knowledge of the distance and relative motion of the system. Here we present very long baseline interferometry (VLBI) observations which reveal that the distance to PSR J0737-3039A/B is batchmode documentclass[fleqn,10pt,legalpaper]{article} usepackage{amssymb} usepackage{amsfonts} usepackage{amsmath} pagestyle{empty} begin{document} (1150_{-160}^{+220}) end{document} parsecs, more than double previous estimates, and confirm its low transverse velocity (∼9 kilometers per second). Combined with a decade of pulsar timing, these results will allow tests of gravitational radiation emission theories at the 0.01% uncertainty level, putting stringent constraints on theories that predict dipolar gravitational radiation. They also allow insight into the systems formation and the source of its high-energy emission.

Discovery of the Young, Energetic Radio Pulsar PSR J1105–6107

We report the discovery and follow-up timing observations of the 63 ms radio pulsar, PSR J1105-6107. The pulsar is young, having a characteristic age of only 63 kyr and, from its dispersion measure, is estimated to be at a distance of ~7 kpc from the Sun. We consider its possible association with the nearby supernova remnant G290.1-0.8 (MSH 11-61A); an association requires that the proper motion of the pulsar be ~22 mas yr-1 (corresponding to ~650 km s-1 for a distance of 7 kpc) directed away from the remnant center, assuming that the characteristic age is the true age. The spin-down luminosity of the pulsar, 2.5 × 1036 ergs s-1, is in the top 1% of all known pulsar spin-down luminosities. Given its estimated distance, PSR J1105-6107 is therefore likely to be observable at high energies. Indeed, it is coincident with the known CGRO/EGRET source 2EG J1103-6106; we consider the possible association and conclude that it is likely.

Timing measurements and their implications for four binary millisecond pulsars

We present timing observations of four millisecond pulsars, using data obtained over three years at the Australia Telescope National Facility (ATNF) Parkes and Nuffield Radio Astronomy Laboratory (NRAL) Jodrell Bank radio telescopes. Astrometric, spin and binary parameters are updated, and substantially improved for three pulsars, PSRs 10613-0200, 11045-4509 and 11643-1224. We have measured the time variation of the projected semimajor axis of the PSR 10437 -4715 orbit due to its proper motion, and use it to constrain the inclination of the orbit and the mass of the companion. Some evidence is found for changes in the dispersion measures of PSRs 11045-4509 and 11643-1224. Limits are placed on the existence of planetary mass companions, ruling out companions with masses and orbits similar to the terrestrial planets of the Solar system for eight pulsars.

Detection of an irradiated pulsar companion

We have detected the optical companion of the eclipsing millisecond pulsar J2051-0827. The amplitude of the companions light curve is at least 1.2 mag, and the variation is consistent with the companions rotating synchronously about the pulsar and one side being heated by the impinging pulsar flux. PSR J2051-0827 is only the second pulsar binary for which direct heating of the companion has been observed. The R magnitude at maximum brightness is 22.3, but we failed to detect any flux from the companion at the phase corresponding to radio eclipse. The absolute magnitude and color temperature suggest that the companion fills its Roche lobe.

The SUrvey for Pulsars and Extragalactic Radio Bursts – I. Survey description and overview

We describe the Survey for Pulsars and Extragalactic Radio Bursts (SUPERB), an ongoing pulsar and fast transient survey using the Parkes radio telescope. SUPERB involves real-time acceleration searches for pulsars and single-pulse searches for pulsars and fast radio bursts. We report on the observational set-up, data analysis, multiwavelength/messenger connections, survey sensitivities to pulsars and fast radio bursts and the impact of radio frequency interference. We further report on the first 10 pulsars discovered in the project. Among these is PSR J1306-40, a millisecond pulsar in a binary system where it appears to be eclipsed for a large fraction of the orbit. PSR J1421-4407 is another binary millisecond pulsar; its orbital period is 30.7 d. This orbital period is in a range where only highly eccentric binaries are known, and expected by theory; despite this its orbit has an eccentricity of 10-5.