Angular momentum alignment of dark matter haloes

In the three years following the discovery of PSR J2051−0827, we have observed a large number of eclipse traverses over a wide frequency range. These data show that the pulsar usually undergoes complete eclipse at frequencies below 1 GHz. At higher frequencies the pulsar is often detected throughout this low-frequency eclipse region with pulse times of arrival being significantly delayed relative to the best-fitting timing model. Variability in the magnitude of the delay is clearly seen and occurs on time-scales shorter than the orbital period. Simultaneous dual frequency observations highlight the difference in the eclipse behaviour for two widely separated frequencies. The low-frequency eclipses are accompanied by a significant decrease in pulsed flux density, while the flux density variations during higher frequency eclipses are not well defined. We consider a number of eclipse mechanisms and find that scattering and cyclotron absorption in the magnetosphere of the companion are consistent with the phenomena presented here.     

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.     

Observations of three slow glitches in the spin rate of the pulsar B1822−09

Three slow glitches in the rotation rate of the pulsar B1822−09 were revealed over the 1995–2004 interval. The slow glitches observed are characterized by a gradual increase in the rotation frequency with a long time-scale of several months, accompanied by a rapid decrease in the magnitude of the frequency first derivative by ∼1–2 per cent of the initial value and subsequent exponential increase back to its initial value on the same time-scale. The cumulative fractional increase in the pulsar rotation rate for the three glitches amounts to  Δν/ν₀∼ 7 × 10⁻⁸  .     

A possible association of a young pulsar (PSR J0855−4644) with the young Vela supernova remnant RX J0852.0−4622

The recently discovered young supernova remnant (SNR) RX J0852.0−4622 has attracted much interest since its discovery because of the possibility that it may have been generated by the nearest supernova in recent history. We note the presence of two Parkes Multibeam Survey pulsars within the boundary of the remnant. We discuss the properties of the two pulsars and the likelihood of either of them being physically linked to the SNR. We tentatively suggest that, given the current uncertainties in the distance to RX J0852.0−4622, one of these pulsars, the 65-ms period PSR J0855−4644 could indeed be the compact remnant of this supernova explosion. If the pulsar birth site is at the geometrical centre of the nebula, then, for the transverse pulsar velocity to be reasonable, the SNR must be nearby (around 250 pc) and no younger than about 3000 yr old.     

High-precision timing of PSR J1600−3053

We present the results of a high-precision timing campaign directed at the binary millisecond pulsar J1600−3053. Submicrosecond pulsar timing has long been the domain of bright, low dispersion measure millisecond pulsars or large diameter telescopes. This experiment, conducted using the Parkes radio telescope in New South Wales, Australia, and utilizing the latest baseband recording hardware, has allowed this pulsar, although distant and faint, to present residuals to a model of its spin behaviour of 650 ns over a period of more than 2 yr. We have also constrained the orbital inclination via Shapiro delay to be between 59° and 70° to 95 per cent confidence and obtained a scintillation velocity measurement indicating a transverse velocity less than 84 km s⁻¹. This pulsar is demonstrating remarkable stability comparable to, and in most cases improving upon, the very best long-term pulsar timing experiments. If this stability is maintained, the current limits on the energy density of the stochastic gravitational wave background will be reached in four more years.     

PSR J1453+1902 and the radio luminosities of solitary versus binary millisecond pulsars

We present 3 yr of timing observations for PSR J1453+1902, a 5.79-ms pulsar discovered during a 430-MHz drift-scan survey with the Arecibo telescope. Our observations show that PSR J1453+1902 is solitary and has a proper motion of  8 ±  2  mas yr⁻¹. At the nominal distance of 1.2 kpc estimated from the pulsar's dispersion measure, this corresponds to a transverse speed of  46 ± 11   km s⁻¹  , typical of the millisecond pulsar population. We analyse the current sample of 55 millisecond pulsars in the Galactic disc and revisit the question of whether the luminosities of isolated millisecond pulsars are different from their binary counterparts. We demonstrate that the apparent differences in the luminosity distributions seen in samples selected from 430-MHz surveys can be explained by small-number statistics and observational selection biases. An examination of the sample from 1400-MHz surveys shows no differences in the distributions. The simplest conclusion from the current data is that the spin, kinematic, spatial and luminosity distributions of isolated and binary millisecond pulsars are consistent with a single homogeneous population.     

Unveiling the thermal and magnetic map of neutron star surfaces though their X-ray emission: method and light-curve analysis

Recent Chandra and XMM–Newton observations of a number of X-ray 'dim' pulsating neutron stars have revealed quite unexpected features in the emission from these sources. Their soft thermal spectrum, believed to originate directly from the star surface, shows evidence for a phase-varying absorption line at some hundred eVs. The pulse modulation is relatively large (pulsed fractions in the range ∼12–35 per cent), the pulse shape is often non-sinusoidal, and the hard X-ray colour appears to be anticorrelated in phase with the total emission. Moreover, the prototype of this class, RX J0720.4−3125, has been found to undergo rather sensible changes in both its spectral and timing properties over a time-scale of a few years. All these new findings seem difficult to reconcile with the standard picture of a cooling neutron star endowed with a purely dipolar magnetic field, at least if surface emission is produced in an atmosphere on top of the crust. In this paper we explore how a dipolar+quadrupolar star-centred field influences the properties of the observed light curves. The phase-resolved spectrum has been evaluated accounting for both radiative transfer in a magnetized atmosphere and general relativistic ray-bending. We computed over 78 000 light curves, varying the quadrupolar components and the viewing geometry. A comparison of the data with our model indicates that higher-order multipoles are required to reproduce the observations.     

Timing of the accreting millisecond pulsar XTE J1814−338

We present a precise timing analysis of the accreting millisecond pulsar XTE J1814−338 during its 2003 outburst, observed by RXTE . A full orbital solution is given for the first time; Doppler effects induced by the motion of the source in the binary system were corrected, leading to a refined estimate of the orbital period,   P _orb= 15 388.7229(2)  s, and of the projected semimajor axis,   a sin  i / c = 0.390633(9)  light-second. We could then investigate the spin behaviour of the accreting compact object during the outburst. We report here a refined value of the spin frequency  (ν= 314.356 108 79(1) Hz)  and the first estimate of the spin frequency derivative of this source while accreting     . This spin-down behaviour arises when both the fundamental frequency and the second harmonic are taken into consideration. We discuss this in the context of the interaction between the disc and the quickly rotating magnetosphere, at accretion rates sufficiently low to allow a threading of the accretion disc in regions where the Keplerian velocity is slower than the magnetosphere velocity. We also present indications of a jitter of the pulse phases around the mean trend, which we argue results from movements of the accreting hotspots in response to variations of the accretion rate.     

A search for the optical and near-infrared counterpart of the accreting millisecond X-ray pulsar XTE J1751−305

We have obtained optical and near-infrared images of the field of the accreting millisecond X-ray pulsar XTE J1751−305. There are no stars in the 0.7-arcsec error circle (0.7 arcsec is the overall uncertainty arising from tying the optical and X-ray images and from the intrinsic uncertainty in the Chandra X-ray astrometric solution). We derive limiting magnitudes for the counterpart of   R > 23.1, I > 21.6, Z > 20.6, J > 19.6  and   K > 19.2  . We compare these upper limits with the magnitudes one would expect for simple models for the possible donor stars and the accretion disc subject to the reddening observed in X-rays for XTE J1751−305 and when put at the distance of the Galactic Centre (8.5 kpc). We conclude that our non-detection does not constrain any of the models for the accretion disc or possible donor stars. Deep, near-infrared images obtained during quiescence will, however, constrain possible models for the donor stars in this ultracompact system.     

Characteristics of the supernova remnant G351.7+0.8 and a distance argument against its association with PSR J1721−3532

New images of the supernova remnant (SNR) G351.7+0.8 are presented based on 21-cm H  i -line emission and continuum emission data from the Southern Galactic Plane Survey. SNR G351.7+0.8 has a flux density of 8.4 ± 0.7 Jy at 1420 MHz. Its spectral index is 0.52 ± 0.25 ( S = v ^−α) between 1420 and 843 MHz, typical of adiabatically expanding shell-like remnants. H  i observations show structures possibly associated with the SNR in the radial velocity range of −10 to −18 km s⁻¹, and suggest a distance of 13.2 kpc and a radius of 30.7 pc. The estimated Sedov age for G351.7+0.8 is less than  6.8×10⁴ yr  . A young radio pulsar PSR J1721−3532 lies close to SNR G351.7+0.8 on the sky. The new distance and age of G351.7+0.8 and recent proper motion measurements of the pulsar strongly argue against an association between SNR G351.7+0.8 and PSR J1721−3532. There is an unidentified, faint X-ray point source 1RXS J172055.3−353937 which is close to G351.7+0.8. This may be a neutron star potentially associated with G351.7+0.8.     

The light curve of the companion to PSR B1957+20

We present a new analysis of the light curve for the secondary star in the eclipsing binary millisecond pulsar system PSR B1957+20. Combining previous data and new data points at minimum from the Hubble Space Telescope , we have 100 per cent coverage in the R -band. We also have a number of new K _s-band data points, which we use to constrain the infrared magnitude of the system. We model this with the eclipsing light-curve (ELC) code. From the modelling with the ELC code we obtain colour information about the secondary at minimum light in BVRI and K . For our best-fitting model we are able to constrain the system inclination to 65°± 2° for pulsar masses ranging from 1.3 to  1.9  M_⊙  . The pulsar mass is unconstrained. We also find that the secondary star is not filling its Roche lobe. The temperature of the unirradiated side of the companion is in agreement with previous estimates and we find that the observed temperature gradient across the secondary star is physically sustainable.     

Chandra and XMM–Newton observations of the low-luminosity X-ray pulsators SAX J1324.4−6200 and SAX J1452.8−5949

We present results from our Chandra and XMM–Newton observations of two low-luminosity X-ray pulsators  SAX J1324.4−6200  and  SAX J1452.8−5949  which have spin periods of 172 and 437 s, respectively. The XMM–Newton spectra for both sources can be fitted well with a simple power-law model of photon index,  Γ∼ 1.0  . A blackbody model can equally well fit the spectra with a temperature,   kT ∼  2 keV, for both sources. During our XMM–Newton observations,  SAX J1324.4−6200  is detected with coherent X-ray pulsations at a period of 172.86 ± 0.02 s while no pulsations with a pulse fraction greater than 18 per cent (at 95 per cent confidence level) in 0.2–12 keV energy band are detected in  SAX J1452.8−5949  . The spin period of  SAX J1324.4−6200  is found to be increasing on a time-scale of     which would suggest that the accretor is a neutron star and not a white dwarf. Using subarcsec spatial resolution of the Chandra telescope, possible counterparts are seen for both sources in the near-infrared images obtained with the son of infrared spectrometer and array camera (SOFI) instrument on the New Technology Telescope. The X-ray and near-infrared properties of  SAX J1324.4−6200  suggest it to be a persistent high-mass accreting X-ray pulsar at a distance  ≤8 kpc  . We identify the near-infrared counterpart of  SAX J1452.8−5949  to be a late-type main-sequence star at a distance ≤10 kpc, thus ruling out  SAX J1452.8−5949  to be a high-mass X-ray binary. However, with the present X-ray and near-infrared observations, we cannot make any further conclusive conclusion about the nature of  SAX J1452.8−5949  .