We present high-precision timing observations spanning up to nine years for 37 millisecond pulsars monitored with the Green Bank and Arecibo radio telescopes as part of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) proje
ct. We describe the observational and instrumental setups used to collect the data, and methodology applied for calculating pulse times of arrival; these include novel methods for measuring instrumental offsets and characterizing low signal-to-noise ratio timing results. The time of arrival data are fit to a physical timing model for each source, including terms that characterize time-variable dispersion measure and frequency-dependent pulse shape evolution. In conjunction with the timing model fit, we have performed a Bayesian analysis of a parameterized timing noise model for each source, and detect evidence for excess low-frequency, or red, timing noise in 10 of the pulsars. For 5 of these cases this is likely due to interstellar medium propagation effects rather than intrisic spin variations. Subsequent papers in this series will present further analysis of this data set aimed at detecting or limiting the presence of nanohertz-frequency gravitational wave signals.
We report the detection of a dispersed Fast Radio Burst (FRB) in archival intermediate-latitude Parkes Radio Telescope data. The burst appears to be of the same physical origin as the four purported extragalactic FRBs reported by Thornton et al. (201
3). This bursts arrival time precedes the Thornton et al.~bursts by ten years. We consider that this survey, and many other archival low-latitude (|gb|<30deg) pulsar surveys, have been searched for FRBs but produced fewer detections than the comparatively brief Thornton et al.~search. Such a rate dependence on Galactic position could provide critical supporting evidence for an extragalactic origin for FRBs. To test this, we form an analytic expression to account for Galactic position and survey setup in FRB rate predictions. Employing a sky temperature, scattering, and dispersion model of the Milky Way, we compute the expected number of FRBs if they are isotropically distributed on the sky w.r.t. Galactic position (i.e. local), and if they are of extragalactic origin. We demonstrate that the relative detection rates reject a local origin with a confidence of 99.96% (~3.6 sigma). The extragalactic predictions provide a better agreement, however are still strong discrepancies with the low-latitude detection rate at a confidence of 99.69% (~2.9 sigma). However, for the extragalactic population, the differences in predicted vs.~detected population may be accounted for by a number of factors, which we discuss.
The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project currently observes 43 pulsars using the Green Bank and Arecibo radio telescopes. In this work we use a subset of 17 pulsars timed for a span of roughly five years (20
05--2010). We analyze these data using standard pulsar timing models, with the addition of time-variable dispersion measure and frequency-variable pulse shape terms. Within the timing data, we perform a search for continuous gravitational waves from individual supermassive black hole binaries in circular orbits using robust frequentist and Bayesian techniques. We find that there is no evidence for the presence of a detectable continuous gravitational wave; however, we can use these data to place the most constraining upper limits to date on the strength of such gravitational waves. Using the full 17 pulsar dataset we place a 95% upper limit on the sky-averaged strain amplitude of $h_0lesssim 3.8times 10^{-14}$ at a frequency of 10 nHz. Furthermore, we place 95% emph{all sky} lower limits on the luminosity distance to such gravitational wave sources finding that the $d_L gtrsim 425$ Mpc for sources at a frequency of 10 nHz and chirp mass $10^{10}{rm M}_{odot}$. We find that for gravitational wave sources near our best timed pulsars in the sky, the sensitivity of the pulsar timing array is increased by a factor of $sim$4 over the sky-averaged sensitivity. Finally we place limits on the coalescence rate of the most massive supermassive black hole binaries.
Six years ago, the discovery of Rotating Radio Transients (RRATs) marked what appeared to be a new type of sparsely-emitting pulsar. Since 2006, more than 70 of these objects have been discovered in single-pulse searches of archival and new surveys.
With a continual inflow of new information about the RRAT population in the form of new discoveries, multi-frequency follow-ups, coherent timing solutions, and pulse rate statistics, a view is beginning to form of the place in the pulsar population RRATs hold. Here we review the properties of neutron stars discovered through single pulse searches. We first seek to clarify the definition of the term RRAT, emphasising that the RRAT population encompasses several phenomenologies. A large subset of RRATs appear to represent the tail of an extended distribution of pulsar nulling fractions and activity cycles; these objects present several key open questions remaining in this field.
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 se
arch 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. PSRJ1900-2600 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.
