Search

The recycling model argues the existence of an evolutionary connection between low mass X-ray binaries and radio millisecond pulsars. The main difficulties which this model finds in predict the parameters of the fully recycled millisecond pulsars, as mass and spin period, can be overcome by the onset of the so-called radio-ejection mechanism. This work is to provide observational support to the radio-ejection mechanism by inspecting the orbital and spin parameters of the known population of fully recycled radio pulsars and compare these with the expectation for the occurrence of this mechanism.

The High Time Resolution Universe survey for pulsars and fast transients has yielded the discovery of a slow radio pulsar, PSR J1622−4950, that despite its high dispersion measure exhibited a highly variable flux density and integrated pulse profile. The pulsar shares many properties with the two previously known magnetars that emit radio pulsations, including a similarly high inferred magnetic field strength. In contrast to other magnetars, PSR J1622−4950 shows no observed variations in X‐ray emission.

We present the evolution of the radio emission from the 2.8‐s pulsar of the double pulsar system PSR J0737−3039A/B. We describe the changes in the pulse profile and flux density over five years of observations, culminating in the B pulsar’s radio disappearance in 2008 March. Over this time, the flux density decreased by 0.177 mJy yr−1 at the brightest orbital phases and the pulse profile evolved from a single to a double peak. Relativistic spin precession, coupled with an elliptical beam, can model the pulse profile evolution well and the reappearance is expected to happen in ∼2035 with the same part of the beam or in ∼2014 if we assume a symmetric beam shape.

The High Time Resolution Universe survey for radio pulsars and transients is the largest such survey yet undertaken with the Parkes radio telescope. We use the 13‐beam multibeam receiver centred at 1352 MHz, connected to BPSR, our new all‐digital backend. This system provides us with 340 MHz of usable band split into 870 channels, each sampled with two bits every 64 μs. The factor of eight improvement in frequency resolution over previous Parkes multibeam surveys allows us to probe further into the galactic plane for short duration signals, such as those from fast transients and millisecond pulsars. The survey is split into low, mid and high Galactic latitude regions, each covered with integration times of 4300, 540 and 270 s respectively. To date we have almost completed the mid latitude survey, discovering 65 previously unknown pulsars, including 15 millisecond pulsars. Upon completion we expect to discover some 400 pulsars, of which 75 will be millisecond pulsars.

The recycling model argues the existence of an evolutionary connection between low mass X‐ray binaries and radio millisecond pulsars. The main difficulties which this model finds in predict the parameters of the fully recycled millisecond pulsars, as mass and spin period, can be overcome by the onset of the so‐called radio‐ejection mechanism. This work is to provide observational support to the radio‐ejection mechanism by inspecting the orbital and spin parameters of the known population of fully recycled radio pulsars and compare these with the expectation for the occurrence of this mechanism.

We have carried out a deep search for radio pulsed emission from the accreting millisecond pulsar XTE J0929‐314 using the Parkes radio telescope. In order to overcome the possible free‐free absorption, caused by matter surrounding the system during the quiescent phase, we performed the observations at high frequencies. No radio pulsations were found down to a limit of 68 μJy at 6.5 GHz and of 26 μJy at 8.5 GHz.We analysed the possible reasons for the non‐detection concluding that beaming factor and intrinsic low luminosity are the most likely explanations.

We have carried out a search for radio pulsed emission from the Accreting Millisecond X‐ray pulsars (AMXPs) XTE J0929‐314, XTE J1751‐305 and XTE J1814‐338 at 6.5 and 8.5 GHz, observed during their X‐Ray quiescent phase. The detection of radio signals, in the quiescent phase of this kind of transient systems, would give a ultimate proof of the recycling model, unambiguously establishing that the AMXPs are the progenitors of the Radio millisecond pulsars. For the first source we can conclude that no radio pulsation is present in the analyzed data down to a limit of 68 μJy at 6.4 GHz and 26 μJy at 8.5 GHz. We discuss several mechanisms that could prevent the detection and suggest that the free‐free absorption cannot be responsible for the lack of a detection, given the relatively high used radio frequencies, while the beaming factor and the intrinsic low luminosity are viable explanations for the non detection of radio pulsation. For the other two sources the work is now in progress.

The double pulsar system PSR J0737-3039A/B is a highly relativistic double neutron star (DNS) binary, with a 2.4-hour orbital period. The low mass of the second-formed NS, as well the low system eccentricity and proper motion, point to a different evolutionary scenario compared to other known DNS systems. We describe analysis of the pulse profile shape over 6 years of observations, and present the resulting constraints on the system geometry. We find the recycled pulsar in this system, PSR J0737-3039A, to have a low misalignment between its spin and orbital angular momentum axes, with a 68.3% upper limit of 6.1 degrees, assuming emission from both magnetic poles. This tight constraint lends credence to the idea that the supernova that formed the second pulsar was relatively symmetric, possibly involving electron-capture onto an O-Ne-Mg core., Comment: 5 page, 2 figures; To appear in the conference proceedings "40 Years of Pulsars: Millisecond Pulsars, Magnetars, and More", August 12-17, 2007, at McGill University, Montreal, Canada. Version with full-resolution figures can be found at http://www.phas.ubc.ca/~ferdman/ferdman.0737_geo.full.ps.gz; typos corrected, some rewording, and references added

Millisecond pulsars in southern globular clusters have been regularly observed for timing pourposes with the Parkes radio telescope. To date, several pulsars have data spanning more than 6 years, and their peculiarities are now recognisable via their timing analysis. In this paper we briefly summarise the state of the art of the timing for the eclipsing binary PSR J1701‐3006B in the clobular cluster NGC6266 and for all the millisecond pulsars in the globualr cluster NGC6752.

Millisecond radio pulsars are magnificent tools for performing a variety of physical and astrophysical investigations, ranging from tests of general relativity to nuclear matter physics, from cosmology to globular cluster dynamics, from plasma physics to binary evolution. The basic properties of these sources, as well as the nature and evolution of their possible progenitors will be first reviewed. Then the focus will be on the main still unanswered issues, with particular emphasis on the link with the accreting millisecond X‐ray pulsars.

Rotating RAdio Transients (RRATs) are a newly discovered astronomical phenomenon, characterised by occasional radio bursts occurring at average intervals ranging from minutes to hours. Analysis of the burst arrival times allowed the identification of periodicities, which fall in the range 0.4 to 7 seconds. For three of them also a secular variation in the periodicity has been measured. In view of these rotational parameters the RRATs seem to be rotating neutron stars, albeit with properties very different from the rest of the population. The characteristics of these sources in the radio band and the X‐ray properties of the first detected counterpart to a RRAT are compared with the multiwavelength properties of other classes of neutron stars trying to explain the nature of RRATs and their connections with known types of objects.

The double pulsar system J0737‐3039A/B is one of the most intriguing pulsar discoveries of the last decade. This binary system, with an orbital period of only 2.4‐hr, provides a truly unique laboratory for relativistic gravity. Its discovery enhances of about an order of magnitude the estimate of the merger rate of double neutron stars systems, opening new possibilities for the current generation of gravitational wave detectors. In this contribution we summarize the present results and look at the prospects of future observations.