Age constraints in the double pulsar system J0737–3039

We investigate the age constraints that can be placed on the double pulsar system using models for the spin-down of the first-born 22.7-ms Pulsar A and the 2.77-s Pulsar B with characteristic ages of 210 and 50 Myr, respectively. Standard models assuming dipolar spin-down of both pulsars suggest that the time since the formation of Pulsar B is ∼50 Myr, that is, close to Pulsar B's characteristic age. However, adopting models which account for the impact of Pulsar A's relativistic wind on Pulsar B's spin-down, we find that the formation of Pulsar B took place either 80 or 180 Myr ago, depending on the interaction mechanism. Formation 80 Myr ago, closer to Pulsar B's characteristic age, would result in the contribution from J0737−3039 to the inferred coalescence rates for double neutron star binaries increasing by 40 per cent. The 180 Myr age is closer to Pulsar A's characteristic age and would be consistent with the most recent estimates of the coalescence rate. The new age constraints do not significantly impact recent estimates of the kick velocity, tilt angle between pre- and post-supernova orbital planes or pre-supernova mass of Pulsar B's progenitor.     

Discovery of a highly dispersed pulsar at l=304°

We report the discovery of a pulsar with a Galactic longitude of 304° and a dispersion measure (DM) of 875 cm⁻³ pc. PSR J1302−63 has the second largest DM of any known pulsar. It is also relatively weak, with a flux density of only 0.2 mJy at 1500 MHz. This is the 13th pulsar with a DM greater than 400 cm⁻³ pc located more than 50° from the Galactic Centre. It provides further evidence for a significant pulsar population and enhanced electron densities within the major spiral arms.     

A new technique for timing the double pulsar system

In 2004, McLaughlin et al. discovered a phenomenon in the radio emission of PSR J0737−3039B (B) that resembles drifting subpulses. The repeat rate of the subpulses is equal to the spin frequency of PSR J0737−3039A (A); this led to the suggestion that they are caused by incidence upon B's magnetosphere of electromagnetic radiation from A. Here, we describe a geometrical model which predicts the delay of B's subpulses relative to A's radio pulses. We show that measuring these delays is equivalent to tracking A's rotation from the point of view of a hypothetical observer located near B. This has three main astrophysical applications: (i) to determine the sense of rotation of A relative to its orbital plane, (ii) to estimate where in B's magnetosphere the radio subpulses are modulated and (iii) to provide an independent estimate of the mass ratio of A and B. The latter might improve existing tests of gravitational theories using this system.     

A timing formula for main-sequence star binary pulsars

In binary radio pulsars with a main-sequence star companion, the spin-induced quadrupole moment of the companion gives rise to a precession of the binary orbit. As a first approximation one can model the secular evolution caused by this classical spin-orbit coupling by linear-in-time changes of the longitude of periastron and the projected semi-major axis of the pulsar orbit. This simple representation of the precession of the orbit neglects two important aspects of the orbital dynamics of a binary pulsar with an oblate companion. First, the quasiperiodic effects along the orbit, owing to the anisotropic 1/ r ³ nature of the quadrupole potential. Secondly, the long-term secular evolution of the binary orbit, which leads to an evolution of the longitude of periastron and the projected semi-major axis, which is non-linear in time.   In this paper a simple timing formula for binary radio pulsars with a main-sequence star companion is presented which models the short-term secular and most of the short-term periodic effects caused by the classical spin-orbit coupling. I also give extensions of the timing formula that account for long-term secular changes in the binary pulsar motion. It is shown that the short-term periodic effects are important for the timing observations of the binary pulsar PSR B1259–63. The long-term secular effects are likely to become important in the next few years of timing observations of the binary pulsar PSR J0045–7319. They could help to restrict or even determine the moments of inertia of the companion star and thus probe its internal structure.   Finally, I reinvestigate the spin-orbit precession of the binary pulsar PSR J0045–7319 since the analysis given in the literature is based on an incorrect expression for the precession of the longitude of periastron. A lower limit of 20° for the inclination of the B star with respect to the orbital plane is derived.     

Can a slowly rotating neutron star be a radio pulsar?

It is shown that the radius of curvature of magnetic field lines in the polar region of a rotating magnetized neutron star can be significantly less than the usual radius of curvature of the dipole magnetic field. The magnetic field in the polar cap is distorted by toroidal electric currents flowing in the neutron star crust. These currents close up the magnetospheric currents driven by the electron–positron plasma generation process in the pulsar magnetosphere. Owing to the decrease in the radius of curvature, electron–positron plasma generation becomes possible even for slowly rotating neutron stars, with   PB ^−2/3₁₂ < 10 s  , where P is the period of star rotation and   B ₁₂= B /10¹² G  is the magnitude of the magnetic field on the star surface.     

Hard X-ray observations of PSR J1833−1034 and its associated pulsar wind nebula

PSR J1833−1034 and its associated pulsar wind nebula (PWN) have been investigated in depth through X-ray observations ranging from 0.1 to 200 keV. The low-energy X-ray data from Chandra reveal a complex morphology that is characterized by a bright central plerion, no thermal shell and an extended diffuse halo. The spectral emission from the central plerion softens with radial distance from the pulsar, with the spectral index ranging from  Γ= 1.61  in the central region to  Γ= 2.36  at the edge of the PWN. At higher energy, INTEGRAL detected the source in the 17–200 keV range. The data analysis clearly shows that the main contribution to the spectral emission in the hard X-ray energy range is originated from the PWN, while the pulsar is dominant above 200 keV. Recent High Energy Stereoscopic System (HESS) observations in the high-energy gamma-ray domain show that PSR J1833−1034 is a bright TeV emitter, with a flux corresponding to ∼2 per cent of the Crab in 1–10 TeV range. In addition, the spectral shape in the TeV energy region matches well with that in the hard X-rays observed by INTEGRAL . Based on these findings, we conclude that the emission from the pulsar and its associated PWN can be described in a scenario where hard X-rays are produced through synchrotron light of electrons with Lorentz factor  γ∼ 10⁹  in a magnetic field of ∼10 μG. In this hypothesis, the TeV emission is due to inverse-Compton interaction of the cooled electrons off the cosmic microwave background photons. Search for PSR J1833−1034 X-ray pulsed emission, via RXTE and Swift X-ray observations, resulted in an upper limit that is about 50 per cent.     

A deep search for pulsar wind nebulae using pulsar gating

Using the Australia Telescope Compact Array (ATCA) we have imaged the fields around five promising pulsar candidates to search for radio pulsar wind nebulae (PWNe). We have used the ATCA in its pulsar-gating mode; this enables an image to be formed containing only off-pulse visibilities, thereby dramatically improving the sensitivity to any underlying PWN. Data from the Molonglo Observatory Synthesis Telescope were also used to provide sensitivity on larger spatial scales. This survey found a faint new PWN around PSR B0906−49; here we report on non-detections of PWNe towards PSRs B1046−58, B1055−52, B1610−50 and J1105−6107. Our radio observations of the field around PSR B1055−52 argue against previous claims of an extended X-ray and radio PWN associated with the pulsar. If these pulsars power unseen, compact radio PWNe, upper limits on the radio flux indicate that a fraction of less than 10⁻⁶ of their spin-down energy is used to power this emission. Alternatively, PSRs B1046−58 and B1610−50 may have relativistic winds similar to other young pulsars and the unseen PWN may be resolved and fainter than our surface brightness sensitivity threshold. We can then determine upper limits on the local interstellar medium (ISM) density of 2.2×10⁻³ and 1×10⁻² cm⁻³, respectively. Furthermore, we derive the spatial velocities of these pulsars to be ∼450 km s⁻¹ and thus rule out the association of PSR B1610−50 with supernova remnant (SNR) G332.4+00.1 (Kes 32). Strong limits on the ratio of unpulsed to pulsed emission are also determined for three pulsars.     

Determination of the orbital parameters of binary pulsars

We present a simple method for determination of the orbital parameters of binary pulsars, using data on the pulsar period at multiple observing epochs. This method uses the circular nature of the velocity space orbit of Keplerian motion and produces preliminary values based on two one-dimensional searches. Preliminary orbital parameter values are then refined using a computationally efficient linear least-squares fit. This method works for random and sparse sampling of the binary orbit. We demonstrate the technique on (i) the highly eccentric binary pulsar PSR J0514−4002 (the first known pulsar in the globular cluster NGC 1851) and (ii) 47 Tuc T, a binary pulsar with a nearly circular orbit.     

Spatially resolved STIS spectra of the gravitationally lensed broad absorption line quasar APM08279+5255: the nature of component C and evidence for microlensing

PSR J1806−2125 is a pulsar discovered in the Parkes multibeam pulsar survey with a rotational period of 0.4 s and a characteristic age of 65 kyr. Between MJDs 51462 and 51894 this pulsar underwent an increase in rotational frequency of  Δ ν / ν ≈16×10^-6  . The magnitude of this glitch is ∼2.5 times greater than any previously observed in any pulsar and 16 times greater than the mean glitch size. This Letter gives the parameters of the glitch and compares its properties with those of previously observed events. The existence of such large and rare glitches offers new hope for attempts to observe thermal X-ray emission from the internal heat released following a glitch, and suggests that pulsars which previously have not been observed to glitch may do so on long time-scales .     

Stellar forensics — II. Millisecond pulsar binaries

We use the grid of models described in Paper I to analyse those millisecond pulsar binaries whose secondaries have been studied optically. In particular, we find cooling ages for these binary systems that range from < 1 to ∼ 15 Gyr. Comparison of cooling ages and characteristic spin-down ages allows us to constrain the initial spin periods and spin-up histories for individual systems, showing that at least some millisecond pulsars had sub-Eddington accretion rates and long magnetic field decay times.     

One-dimensional electric field structure of an outer gap accelerator – III. Location of the gap and the gamma-ray spectrum

We investigate a stationary particle acceleration zone in the outer magnetosphere of an obliquely rotating neutron star. The charge depletion as a result of global current causes a large electric field along the magnetic field lines. Migratory electrons and/or positrons are accelerated by this field to radiate curvature gamma-rays, some of which collide with the X-rays to materialize as pairs in the gap. As a result of this pair-production cascade, the replenished charges partially screen the electric field, which is self-consistently solved together with the distribution of particles and gamma-rays. If no current is injected at either of the boundaries of the accelerator, the gap is located around the so-called null surface, where the local Goldreich–Julian charge density vanishes. However, we find that the gap position shifts outwards (or inwards) when particles are injected at the inner (or outer) boundary. We apply the theory to the seven pulsars whose X-ray fields are known from observations. We show that the gap should be located near to or outside of the null surface for the Vela pulsar and PSR B1951+32, so that their expected GeV spectrum may be consistent with observations. We then demonstrate that the intrinsically large TeV flux from the outer gap of PSR B0540–69 is absorbed by the magnetospheric infrared photons, causing it to be undetectable. We also point out that the electrodynamic structure and the resultant GeV emission properties of millisecond pulsars are similar to young pulsars.