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.

This catalog summarizes 117 high-confidence 0.1 GeV gamma-ray pulsar detections using three years of data acquired by the Large Area Telescope (LAT) on the Fermi satellite. Half are neutron stars discovered using LAT data through periodicity searches in gamma-ray and radio data around LAT unassociated source positions. The 117 pulsars are evenly divided into three groups: millisecond pulsars, young radio-loud pulsars, and young radio-quiet pulsars. We characterize the pulse profiles and energy spectra and derive luminosities when distance information exists. Spectral analysis of the off-peak phase intervals indicates probable pulsar wind nebula emission for four pulsars, and off-peak magnetospheric emission for several young and millisecond pulsars. We compare the gammaray properties with those in the radio, optical, and X-ray bands. We provide flux limits for pulsars with no observed gamma-ray emission, highlighting a small number of gamma-faint, radio-loud pulsars. The large, varied gamma-ray pulsar sample constrains emission models. Fermi's selection biases complement those of radio surveys, enhancing comparisons with predicted population distributions.

Gravitational waves are expected to be radiated by supermassive black hole binaries formed during galaxy mergers. A stochastic superposition of gravitational waves from all such binary systems will modulate the arrival times of pulses from radio pulsars. Using observations of millisecond pulsars obtained with the Parkes radio telescope, we constrain the characteristic amplitude of this background, A c,yr , to be < 1.0×10-15 with 95% confidence. This limit excludes predicted ranges for A c,yr from current models with 91-99.7% probability. We conclude that binary evolution is either stalled or dramatically accelerated by galactic-center environments, and that higher-cadence and shorter-wavelength observations would result in an increased sensitivity to gravitational waves.Studies of the dynamics of stars and gas in nearby galaxies provide strong evidence for the ubiquity of supermassive (> 10 6 solar mass) black holes (SMBHs) (1). Observations of luminous quasars indicate that SMBHs are hosted by galaxies throughout the history of the universe (2) and affect global properties of the host galaxies (3). The prevailing dark energycold dark matter cosmological paradigm predicts that large galaxies are assembled through the hierarchical merging of smaller galaxies. The remnants of mergers can host gravitationally bound binary SMBHs with orbits decaying through the emission of gravitational waves (GWs) (4).Gravitational waves from binary SMBHs, with periods between ~ 0.1 and 30 yr (5), can be detected or constrained by monitoring, for years to decades, a set of rapidly rotating millisecond pulsars (MSPs) distributed throughout our galaxy. Radio emission beams from MSPs are observed as pulses that can be time-tagged with as small as 20 ns precision (6). When traveling across the pulsar-Earth line of sight, GWs induce variations in the arrival times of the pulses (7).The superposition of GWs from the binary SMBH population is a stochastic background (GWB), which is typically characterized by the strain-amplitude spectrum h c (f)=A c,yr [f/(1 yr -1 )] -2/3 , where f is the GW frequency, A c,yr is the characteristic amplitude of the GWB measured at f = 1 yr -1 , predicted to be A c,yr > 10 -15 (5,(8)(9)(10)(11)(12), and -2/3 is the predicted spectral index (5,(8)(9)(10)(11)(12). The GWB will add low-frequency perturbations to pulse arrival times. While the detection of the GWB would confirm the presence of a cosmological population of binary SMBHs, limits on its amplitude constrain models of galaxy and SMBH evolution (8).As part of the Parkes Pulsar Timing Array project to detect GWs (6), we have been monitoring 24 pulsars with the 64-m Parkes radio telescope. We have produced a new data set, using observations taken at a central wavelength of 10 cm and previously reported methods (6,8), that spans 11 yr, which is 3 yr longer than previous data sets analyzed at this wavelength. In addition to having greater sensitivity to the GWB because of the longer duration, the data set was improved by identifying and correc...

The highly stable spin of neutron stars can be exploited for a variety of (astro-)physical investigations. In particular arrays of pulsars with rotational periods of the order of milliseconds can be used to detect correlated signals such as those caused by gravitational waves. Three such "Pulsar Timing Arrays" (PTAs) have been set up around the world over the past decades and collectively form the "International" PTA (IPTA). In this paper, we describe the first joint analysis of the data from the three regional PTAs, i.e. of the first IPTA data set. We describe the available PTA data, the approach presently followed for its combination and suggest improvements for future PTA research. Particular attention is paid to subtle details (such as underestimation of measurement uncertainty and long-period noise) that have often been ignored but which become important in this unprecedentedly large and inhomogeneous data set. We identify and describe in detail several factors that complicate IPTA research and provide recommendations for future pulsar timing efforts. The first IPTA data release presented here (and available online) is used to demonstrate the IPTA's potential of improving upon gravitational-wave limits placed by individual PTAs by a factor of ∼ 2 and provides a 2 − σ limit on the dimensionless amplitude of a stochastic GWB of 1.7 × 10 −15 at a frequency of 1 yr −1 . This is 1.7 times less constraining than the limit placed by , due mostly to the more recent, high-quality data they used. c 2015 RAS c 2015 RAS, MNRAS 000, 1-25 First IPTA Data Release 3 σJitter ∝ fJW eff 1 + m 2 I Np ,with fJ the jitter parameter, which needs to be determined experimentally (Liu et al. 2012;Shannon et al. 2014); W eff the pulse width; mI = σE/µE the modulation index, defined by the mean (µE) and standard deviation (σE) of the pulseenergy distribution; and Np = tint/P the number of pulses in the observation, which equals the total observing time divided by the pulse period. Consequently, the highest-precision timing efforts ideally require rapidly rotating pulsars (P 0.03 s) with high relatively flux densities (S1.4 GHz 0.5 mJy) and narrow pulses (δ 20%) are observed at sensitive (A eff /Tsys) telescopes with wide-bandwidth receivers (∆f ) and for long integration times (tint 30 min).

We present timing models for 20 millisecond pulsars in the Parkes Pulsar Timing Array. The precision of the parameter measurements in these models has been improved over earlier results by using longer data sets and modelling the non-stationary noise. We describe a new noise modelling procedure and demonstrate its effectiveness using simulated data. Our methodology includes the addition of annual dispersion measure (DM) variations to the timing models of some pulsars. We present the first significant parallax measurements for PSRs J1024−0719, J1045−4509, J1600−3053, J1603−7202, and J1730−2304, as well as the first significant measurements of some post-Keplerian orbital parameters in six binary pulsars, caused by kinematic effects. Improved Shapiro delay measurements have resulted in much improved pulsar mass measurements, particularly for PSRs J0437−4715 and J1909−3744 with M p = 1.44 ± 0.07 M and M p = 1.47 ± 0.03 M respectively. The improved orbital period-derivative measurement for PSR J0437−4715 results in a derived distance measurement at the 0.16% level of precision, D = 156.79 ± 0.25 pc, one of the most fractionally precise distance measurements of any star to date.

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 mu s. 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 similar to 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

A 'pulsar timing array' (PTA), in which observations of a large sample of pulsars spread across the celestial sphere are combined, allows investigation of 'global' phenomena such as a background of gravitational waves or instabilities in atomic timescales that produce correlated timing residuals in the pulsars of the array. The Parkes Pulsar Timing Array (PPTA) is an implementation of the PTA concept based on observations with the Parkes 64-m radio telescope. A sample of 20 ms pulsars is being observed at three radio-frequency bands, 50 cm (ß700 MHz), 20 cm (ß1400 MHz), and 10 cm (ß3100 MHz), with observations at intervals of two to three weeks. Regular observations commenced in early 2005. This paper describes the systems used for the PPTA observations and data processing, including calibration and timing analysis. The strategy behind the choice of pulsars, observing parameters, and analysis methods is discussed. Results are presented for PPTA data in the three bands taken between 2005 March and 2011 March. For 10 of the 20 pulsars, rms timing residuals are less than 1 μs for the best band after fitting for pulse frequency and its first time derivative. Significant 'red' timing noise is detected in about half of the sample. We discuss the implications of these results on future projects including the International Pulsar Timing Array and a PTA based on the Square Kilometre Array. We also present an 'extended PPTA' data set that combines PPTA data with earlier Parkes timing data for these pulsars.

As part of a survey for radio pulsars with the Parkes 64-m telescope we have discovered PSR J1622-4950, a pulsar with a 4.3-s rotation period. Follow-up observations show that the pulsar has the highest inferred surface magnetic field of the known radio pulsars (B∼3×10 14 G), exhibits significant timing noise and appears to have an inverted spectrum. Unlike the vast majority of the known pulsar population, PSR J1622-4950 appears to switch off for many hundreds of days and even in its on-state exhibits extreme variability in its flux density. Furthermore, the integrated pulse profile changes shape with epoch. All of these properties are remarkably similar to the only two magnetars previously known to emit radio pulsations. The position of PSR J1622-4950 is coincident with an X-ray source that, unlike the other radio pulsating magnetars, was found to be in quiescence. We conclude that our newly discovered pulsar is a magnetar -the first to be discovered via its radio emission.