The Parkes Multibeam Pulsar Survey is a sensitive survey of a strip of the Galactic plane with |b| < 5° and 260° < l < 50° at 1374 MHz. Here we report the discovery of 120 new pulsars and subsequent ...timing observations, primarily using the 76-m Lovell radio telescope at Jodrell Bank. The main features of the sample of 370 published pulsars discovered during the multibeam survey are described. Furthermore, we highlight two pulsars: PSR J1734−3333, a young pulsar with the second highest surface magnetic field strength among the known radio pulsars, Bs= 5.4 × 1013 G, and PSR J1830−1135, the second slowest radio pulsar known, with a 6-s period.
Searches for transient astrophysical sources often reveal unexpected classes of objects that are useful physical laboratories. In a recent survey for pulsars and fast transients, we have uncovered ...four millisecond-duration radio transients all more than 40° from the Galactic plane. The bursts' properties indicate that they are of celestial rather than terrestrial origin. Host galaxy and intergalactic medium models suggest that they have cosmological redshifts of 0.5 to 1 and distances of up to 3 gigaparsecs. No temporally coincident x-or gamma-ray signature was identified in association with the bursts. Characterization of the source population and identification of host galaxies offers an opportunity to determine the baryonic content of the universe.
We report the discovery of X-ray pulsations at 105.2 Hz (9.5 ms) from the transient X-ray binary IGR J16597–3704 using NuSTAR and Swift. The source was discovered by INTEGRAL in the globular cluster ...NGC 6256 at a distance of 9.1 kpc. The X-ray pulsations show a clear Doppler modulation that implies an orbital period of ~46 min and a projected semi-major axis of ~5 lt-ms, which makes IGR J16597–3704 an ultracompact X-ray binary system. We estimated a minimum companion mass of 6.5 × 10−10 M⊙, assuming a neutron star mass of 1.4 M⊙, and an inclination angle of <75° (suggested by the absence of eclipses or dips in its light curve). The broad-band energy spectrum of the source is well described by a disk blackbody component (kT ~ 1.4 keV) plus a comptonised power-law with photon index ~2.3 and an electron temperature of ~30 keV. Radio pulsations from the source were unsuccessfully searched for with the Parkes Observatory.
We report on the pulse-to-pulse energy distributions and phase-resolved modulation properties for catalogued pulsars in the southern High Time Resolution Universe intermediate-latitude survey. We ...selected the 315 pulsars detected in a single-pulse search of this survey, allowing a large sample unbiased regarding any rotational parameters of neutron stars. We found that the energy distribution of many pulsars is well described by a log-normal distribution, with few deviating from a small range in log-normal scale and location parameters. Some pulsars exhibited multiple energy states corresponding to mode changes, and implying that some observed 'nulling' may actually be a mode-change effect. PSR J1900−2600 was found to emit weakly in its previously identified 'null' state. We found evidence for another state-change effect in two pulsars, which show bimodality in their nulling time-scales; that is, they switch between a continuous-emission state and a single-pulse-emitting state. Large modulation occurs in many pulsars across the full integrated profile, with increased sporadic bursts at leading and trailing sub-beam edges. Some of these high-energy outbursts may indicate the presence of 'giant pulse' phenomena. We found no correlation with modulation and pulsar period, age or other parameters. Finally, the deviation of integrated pulse energy from its average value was generally quite small, despite the significant phase-resolved modulation in some pulsars; we interpret this as tenuous evidence of energy regulation between distinct pulsar sub-beams.
Direct detection of low-frequency gravitational waves (GWs,
Hz) is the main goal of pulsar timing array (PTA) projects. One of the main targets for the PTAs is to measure the stochastic background of ...gravitational waves (GWB) whose characteristic strain is expected to approximately follow a power-law of the form
, where f is the GW frequency. In this paper we use the current data from the European PTA to determine an upper limit on the GWB amplitude A as a function of the unknown spectral slope α with a Bayesian algorithm, by modelling the GWB as a random Gaussian process. For the case α=−2/3, which is expected if the GWB is produced by supermassive black hole binaries, we obtain a 95 per cent confidence upper limit on A of 6 × 10−15, which is 1.8 times lower than the 95 per cent confidence GWB limit obtained by the Parkes PTA in 2006. Our approach to the data analysis incorporates the multitelescope nature of the European PTA and thus can serve as a useful template for future intercontinental PTA collaborations.
We have embarked on a survey for pulsars and fast transients using the 13-beam multibeam receiver on the Parkes Radio Telescope. Installation of a digital backend allows us to record 400 MHz of ...bandwidth for each beam, split into 1024 channels and sampled every 64 μs. Limits of the receiver package restrict us to a 340 MHz observing band centred at 1352 MHz. The factor of 8 improvement in frequency resolution over previous multibeam surveys allows us to probe deeper into the Galactic plane for short-duration signals such as the pulses from millisecond pulsars. We plan to survey the entire southern sky in 42 641 pointings, split into low, mid and high Galactic latitude regions, with integration times of 4200, 540 and 270 s, respectively. Simulations suggest that we will discover 400 pulsars, of which 75 will be millisecond pulsars. With ∼30 per cent of the mid-latitude survey complete, we have redetected 223 previously known pulsars and discovered 27 pulsars, five of which are millisecond pulsars. The newly discovered millisecond pulsars tend to have larger dispersion measures than those discovered in previous surveys, as expected from the improved time and frequency resolution of our instrument.
We have used millisecond pulsars (MSPs) from the southern High Time Resolution Universe (HTRU) intermediate latitude survey area to simulate the distribution and total population of MSPs in the ...Galaxy. Our model makes use of the scalefactor method, which estimates the ratio of the total number of MSPs in the Galaxy to the known sample. Using our best-fitting value for the z-height, z = 500 pc, we find an underlying population of MSPs of 8.3(±4.2) × 104 sources down to a limiting luminosity of L
min = 0.1 mJy kpc2 and a luminosity distribution with a steep slope of d log N/d log L = −1.45 ± 0.14. However, at the low end of the luminosity distribution, the uncertainties introduced by small number statistics are large. By omitting very low luminosity pulsars, we find a Galactic population above L
min = 0.2 mJy kpc2 of only 3.0(±0.7) × 104 MSPs. We have also simulated pulsars with periods shorter than any known MSP, and estimate the maximum number of sub-MSPs in the Galaxy to be 7.8(±5.0) × 104 pulsars at L = 0.1 mJy kpc2. In addition, we estimate that the high and low latitude parts of the southern HTRU survey will detect 68 and 42 MSPs, respectively, including 78 new discoveries. Pulsar luminosity, and hence flux density, is an important input parameter in the model. Some of the published flux densities for the pulsars in our sample do not agree with the observed flux densities from our data set, and we have instead calculated average luminosities from archival data from the Parkes Telescope. We found many luminosities to be very different than their catalogue values, leading to very different population estimates. Large variations in flux density highlight the importance of including scintillation effects in MSP population studies.
We present the search methods and initial results for transient radio signals in the High Time Resolution Universe (HTRU) survey. The HTRU survey's single-pulse search, the software designed to ...perform the search and a determination of the HTRU survey's sensitivity to single pulses are described. Initial processing of a small fraction of the survey has produced 11 discoveries, all of which are sparsely emitting neutron stars, as well as provided confirmation of two previously unconfirmed neutron stars. Most of the newly discovered objects lie in regions surveyed previously, indicating both the improved sensitivity of the HTRU survey observing system and the dynamic nature of the radio sky. The cycles of active and null states in nulling pulsars, rotating radio transients (RRATs) and long-term intermittent pulsars are explored in the context of determining the relationship between these populations and of the sensitivity of a search to the various radio-intermittent neutron star populations. This analysis supports the case that many RRATs are in fact high-null-fraction pulsars (i.e. with a null fraction of ≳0.95) and indicates that intermittent pulsars appear distinct from nulling pulsars in their activity cycle time-scales. We find that in the measured population, there is a deficit of pulsars with typical emission time-scales greater than ∼300 s that is not readily explained by selection effects. The HTRU low-latitude survey will be capable of addressing whether this deficit is physical. We predict that the HTRU survey will explore pulsars with a broad range of nulling fractions (up to and beyond 0.999), and at its completion is likely to increase the currently known RRATs by a factor of more than 2.
The double pulsar system PSR J0737-3039A/B is unique in that both neutron stars are detectable as radio pulsars. They are also known to have much higher mean orbital velocities and accelerations than ...those of other binary pulsars. The system is therefore a good candidate for testing Einstein's theory of general relativity and alternative theories of gravity in the strong-field regime. We report on precision timing observations taken over the 2.5 years since its discovery and present four independent strong-field tests of general relativity. These tests use the theory-independent mass ratio of the two stars. By measuring relativistic corrections to the Keplerian description of the orbital motion, we find that the "post-Keplerian" parameter s agrees with the value predicted by general relativity within an uncertainty of 0.05%, the most precise test yet obtained. We also show that the transverse velocity of the system's center of mass is extremely small. Combined with the system's location near the Sun, this result suggests that future tests of gravitational theories with the double pulsar will supersede the best current solar system tests. It also implies that the second-born pulsar may not have formed through the core collapse of a helium star, as is usually assumed.
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