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.

We present a new model for the distribution of free electrons in the Galaxy, the Magellanic Clouds, and the intergalactic medium (IGM) that can be used to estimate distances to real or simulated pulsars and fast radio bursts (FRBs) based on their dispersion measure (DM). The Galactic model has an extended thick disk representing the so-called warm interstellar medium, a thin disk representing the Galactic molecular ring, spiral arms based on a recent fit to Galactic H II regions, a Galactic Center disk, and seven local features including the Gum Nebula, Galactic Loop I, and the Local Bubble. An offset of the Sun from the Galactic plane and a warp of the outer Galactic disk are included in the model. Parameters of the Galactic model are determined by fitting to 189 pulsars with independently determined distances and DMs. Simple models are used for the Magellanic Clouds and the IGM. Galactic model distances are within the uncertainty range for 86 of the 189 independently determined distances and within 20% of the nearest limit for a further 38 pulsars. We estimate that 95% of predicted Galactic pulsar distances will have a relative error of less than a factor of 0.9. The predictions of YMW16 are compared to those of the TC93 and NE2001 models showing that YMW16 performs significantly better on all measures. Timescales for pulse broadening due to interstellar scattering are estimated for (real or simulated) Galactic and Magellanic Cloud pulsars and FRBs.

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.

A nanohertz-frequency stochastic gravitational-wave background can potentially be detected through the precise timing of an array of millisecond pulsars. This background produces low-frequency noise in the pulse arrival times that would have a characteristic spectrum common to all pulsars and a well-defined spatial correlation. Recently the North American Nanohertz Observatory for Gravitational Waves collaboration (NANOGrav) found evidence for the common-spectrum component in their 12.5 yr data set. Here we report on a search for the background using the second data release of the Parkes Pulsar Timing Array. If we are forced to choose between the two NANOGrav models—one with a common-spectrum process and one without—we find strong support for the common-spectrum process. However, in this paper, we consider the possibility that the analysis suffers from model misspecification. In particular, we present simulated data sets that contain noise with distinctive spectra but show strong evidence for a common-spectrum process under the standard assumptions. The Parkes data show no significant evidence for, or against, the spatially correlated Hellings–Downs signature of the gravitational-wave background. Assuming we did observe the process underlying the spatially uncorrelated component of the background, we infer its amplitude to be A = 2.2 − 0.3 + 0.4 × 10 − 15 in units of gravitational-wave strain at a frequency of 1 yr−1. Extensions and combinations of existing and new data sets will improve the prospects of identifying spatial correlations that are necessary to claim a detection of the gravitational-wave background.

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.

Signals from radio pulsars show a wavelength-dependent delay due to dispersion in the interstellar plasma. At a typical observing wavelength, this delay can vary by tens of microseconds on five-year time scales, far in excess of signals of interest to pulsar timing arrays, such as that induced by a gravitational-wave background. Measurement of these delay variations is not only crucial for the detection of such signals, but also provides an unparallelled measurement of the turbulent interstellar plasma at au scales.In this paper we demonstrate that without consideration of wavelengthindependent red-noise, 'simple' algorithms to correct for interstellar dispersion can attenuate signals of interest to pulsar timing arrays. We present a robust method for this correction, which we validate through simulations, and apply it to observations from the Parkes Pulsar Timing Array. Correction for dispersion variations comes at a cost of increased band-limited white noise. We discuss scheduling to minimise this additional noise, and factors, such as scintillation, that can exacerbate the problem.Comparison with scintillation measurements confirms previous results that the spectral exponent of electron density variations in the interstellar medium often appears steeper than expected. We also find a discrete change in dispersion measure of PSR J1603−7202 of ∼ 2×10 −3 cm −3 pc for about 250 days. We speculate that this has a similar origin to the 'extreme scattering events' seen in other sources. In addition, we find that four pulsars show a wavelength-dependent annual variation, indicating a persistent gradient of electron density on an au spatial scale, which has not been reported previously.