No abstract

We present and analyse a catalogue of 233 pulsars with proper motion measurements. The sample contains a wide variety of pulsars including recycled objects and those associated with globular clusters or supernova remnants. After taking the most precise proper motions for those pulsars for which multiple measurements are available, the majority of the proper motions (58%) are derived from pulsar timing methods, 41% using interferometers and the remaining 1% using optical telescopes. Many of the 1-D and 2-D speeds (referring to speeds measured in one coordinate only and the magnitudes of the transverse velocities respectively) derived from these measurements are somewhat lower than earlier estimates because of the use of the most recent electron density model in determining pulsar distances. The mean 1-D speeds for the normal and recycled pulsars are 152(10) and 54(6) km/s respectively. The corresponding mean 2-D speeds are 246(22) and 87(13) km/s. PSRs B2011+38 and B2224+64 have the highest inferred 2-D speeds of ~1600 km/s. We study the mean speeds for different subsamples and find that, in general, they agree with previous results. Applying a novel deconvolution technique to the sample of 73 pulsars with characteristic ages less than 3 Myr, we find the mean 3-D pulsar birth velocity to be 400(40) km/s. The distribution of velocities is well described by a Maxwellian distribution with 1-D rms sigma=265 km/s. There is no evidence for a bimodal velocity distribution. The proper motions for PSRs B1830-08 and B2334+61 are consistent with their proposed associations with the supernova remnants W41 and G114.3+0.3 respectively.Comment: 20 pages, accepted by MNRA

Despite its importance to our understanding of physics at supranuclear densities, the equation of state (EoS) of matter deep within neutron stars remains poorly understood. Millisecond pulsars (MSPs) are among the most useful astrophysical objects in the Universe for testing fundamental physics, and place some of the most stringent constraints on this high-density EoS. Pulsar timing -the process of accounting for every rotation of a pulsar over long time periods -can precisely measure a wide variety of physical phenomena, including those that allow the measurement of the masses of the components of a pulsar binary system [1]. One of these, called relativistic Shapiro delay [2], can yield precise masses for both an MSP and its companion; however, it is only easily observed in a small subset of high-precision, highly inclined (nearly edge-on) binary pulsar systems. By combining data from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 12.5-year data set with recent orbital-phase-specific observations using the Green Bank Telescope, we have measured the mass of the MSP J0740+6620 to be 2.14 +0.10 −0.09 solar masses (68.3% credibility interval; 95.4% credibility interval is 2.14 +0.20 −0.18 solar masses). It is highly 1 arXiv:1904.06759v2 [astro-ph.HE] 13 Sep 2019 likely to be the most massive neutron star yet observed, and serves as a strong constraint on the neutron star interior EoS. Relativistic Shapiro delay, which is observable when a pulsar passes behind its stellar companion during orbital conjunction, manifests as a small delay in pulse arrival times induced by the curvature of spacetime in the vicinity of the companion star. For a highly inclined MSP-white dwarf binary, the full delay is of order ∼10 µs. The relativistic effect is characterized by two parameters, "shape" and "range." In general relativity, shape (s) is the sine of the angle of inclination of the binary orbit (i), while range (r) is proportional to the mass of the companion, m c . When combined with the Keplerian mass function, measurements of r and s also constrain the pulsar mass (m p ; [3] provides a detailed overview and an alternate parameterization).Precise neutron star mass measurements are an effective way to constrain the EoS of the ultradense matter in neutron star interiors. Although radio pulsar timing cannot directly determine neutron star radii, the existence of pulsars with masses exceeding the maximum mass allowed by a given model can straightforwardly rule out that EoS.In 2010, Demorest et al. reported the discovery of a 2-solar-mass MSP, J1614−2230 [4] (though the originally reported mass was 1.97 ± 0.04 M , continued timing has led to a more precise mass measurement of 1.928±0.017 M ; Fonseca et al. 2016 [5]). This Shapiro-delay-enabled measurement disproved the plausibility of some hyperon, boson, and free quark models in nuclear-density environments. In 2013, Antoniadis et al. used optical techniques in combination with pulsar timing to yield a mass measurement of 2.01±0.04 M for the pulsar J0...

We search for an isotropic stochastic gravitational-wave background (GWB) in the 12.5 yr pulsar-timing data set collected by the North American Nanohertz Observatory for Gravitational Waves. Our analysis finds strong evidence of a stochastic process, modeled as a power law, with common amplitude and spectral slope across pulsars. Under our fiducial model, the Bayesian posterior of the amplitude for an f −2/3 power-law spectrum, expressed as the characteristic GW strain, has median 1.92 × 10−15 and 5%–95% quantiles of 1.37–2.67 × 10−15 at a reference frequency of f yr = 1 yr − 1 ; the Bayes factor in favor of the common-spectrum process versus independent red-noise processes in each pulsar exceeds 10,000. However, we find no statistically significant evidence that this process has quadrupolar spatial correlations, which we would consider necessary to claim a GWB detection consistent with general relativity. We find that the process has neither monopolar nor dipolar correlations, which may arise from, for example, reference clock or solar system ephemeris systematics, respectively. The amplitude posterior has significant support above previously reported upper limits; we explain this in terms of the Bayesian priors assumed for intrinsic pulsar red noise. We examine potential implications for the supermassive black hole binary population under the hypothesis that the signal is indeed astrophysical in nature.

The double pulsar system, PSR J0737-3039A/B, is unique in that both neutron stars are detectable as radio pulsars. This, combined with significantly higher mean orbital velocities and accelerations when compared to other binary pulsars, suggested that the system would become the best available testbed for general relativity and alternative theories of gravity in the strong-field regime. 1Here 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. Use of the theory-independent mass ratio of the two stars makes these tests uniquely different from earlier studies. By measuring relativistic corrections to the Keplerian discription of the orbital motion, we find that the "postKeplerian" parameter s agrees with the value predicted by Einstein's theory of 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 have formed differently to the usually assumed core-collapse of a helium star.

The clock-like properties of pulsars moving in the gravitational fields of their unseen neutron-star companions have allowed unique tests of general relativity and provided evidence for gravitational radiation. We report here the detection of the 2.8-sec pulsar J0737−3039B as the companion to the 23-ms 1

The merger 1 of close binary systems containing two neutron stars should produce a burst of gravitational waves, as predicted by the theory of general relativity 2 . A reliable estimate of the double-neutron-star merger rate in the Galaxy is crucial in order to predict whether current gravity wave detectors will be successful in detecting such bursts. Present estimates of this rate are rather low 3−7 , because we know of only a few doubleneutron-star binaries with merger times less than the age of the Universe. Here we report the discovery of a 22-ms pulsar, PSR J0737−3039, which is a member of a highly relativistic double-neutron-star binary with an orbital period of 2.4 hours. This system will merge in about 85 Myr, a time much shorter than for any other known neutron-star binary. Together with the relatively low radio luminosity of PSR J0737−3039, this timescale implies an order-of-magnitude increase in the predicted merger rate for double-neutron-star systems in our Galaxy (and in the rest of the Universe). PSR J0737−3039 was discovered during a pulsar search carried out using a multibeam receiver 8 on the Parkes 64-m radio telescope in New South Whales, Australia. The original detection showed a large change in apparent pulsar period during the 4-min observation time, suggesting that the pulsar is a member of a tight binary system. Follow-up observations undertaken at Parkes consisting of continuous ∼ 5-hour observations showed that the orbit has a very short period (2.4 hrs) and a significant eccentricity (0.088). The derived orbital parameters implied that the system is relatively massive, probably consisting of two neutron stars, and predicted a huge rate of periastron advanceω due to effects of general relativity. Indeed, after only a few days of pulse-timing observations we were able to detect a significant value ofω.Interferometric observations made using the Australia Telescope Compact Array (ATCA) in the 20-cm band gave an improved position and flux density for the pulsar. Knowledge of the pulsar position with subarcsecond precision allowed determination of the rotational period derivative,Ṗ , and other parameters from the available data span. Table 1 reports results derived from a coherent phase fit to data taken over about five months. The measured value ofω = 16.88 • yr −1 is about four times that of PSR B1913+16 (ref. 9), previously the highestknown. If the observedω is entirely due to general relativity, it indicates a total system mass M = 2.58 ± 0.02 M , where M is the mass of the Sun. Figure 1 shows the constraints on the masses of the pulsar and its companion resulting from the observations so far and the mean pulse profile as an inset. The shaded region indicates values that are ruled out by the mass function M f and the observeḋ ω constrains the system to lie between the two diagonal lines. Together, these constraints imply that the pulsar mass m p is less than 1.35 M and that the companion mass m c is greater than 1.24 M . The derived upper limit on m p is consistent with the

The radio sky is relatively unexplored for transient signals, although the potential of radio-transient searches is high. This was demonstrated recently by the discovery of a previously unknown type of source, varying on timescales of minutes to hours. Here we report a search for radio sources that vary on much shorter timescales. We found eleven objects characterized by single, dispersed bursts having durations between 2 and 30ms. The average time intervals between bursts range from 4min to 3h with radio emission typically detectable for <1s per day. From an analysis of the burst arrival times, we have identified periodicities in the range 0.4-7s for ten of the eleven sources, suggesting origins in rotating neutron stars. Despite the small number of sources detected at present, their ephemeral nature implies a total Galactic population significantly exceeding that of the regularly pulsing radio pulsars. Five of the ten sources have periods >4s, and the rate of change of the pulse period has been measured for three of them; for one source, we have inferred a high magnetic field strength of 5 × 1013G. This suggests that the new population is related to other classes of isolated neutron stars observed at X-ray and γ-ray wavelengths