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Register a new userSolar System Ephemerides, Pulsar Timing, Gravitational Waves, and Navigation
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T. Joseph W. Lazio
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In-spiraling supermassive black holes should emit gravitational waves, which would produce characteristic distortions in the time of arrival residuals from millisecond pulsars. Multiple national and regional consortia have constructed pulsar timing arrays by precise timing of different sets of millisecond pulsars. An essential aspect of precision timing is the transfer of the times of arrival to a (quasi-)inertial frame, conventionally the solar system barycenter. The barycenter is determined from the knowledge of the planetary masses and orbits, which has been refined over the past 50 years by multiple spacecraft. Within the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), uncertainties on the solar system barycenter are emerging as an important element of the NANOGrav noise budget. We describe what is known about the solar system barycenter, touch upon how uncertainties in it affect gravitational wave studies with pulsar timing arrays, and consider future trends in spacecraft navigation.
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The regularity of pulsar emissions becomes apparent once we reference the pulses times of arrivals to the inertial rest frame of the solar system. It follows that errors in the determination of Earths position with respect to the solar-system barycenter can appear as a time-correlated bias in pulsar-timing residual time series, affecting the searches for low-frequency gravitational waves performed with pulsar timing arrays. Indeed, recent array datasets yield different gravitational-wave background upper limits and detection statistics when analyzed with different solar-system ephemerides. Crucially, the ephemerides do not generally provide usable error representations. In this article we describe the motivation, construction, and application of a physical model of solar-system ephemeris uncertainties, which focuses on the degrees of freedom (Jupiters orbital elements) most relevant to gravitational-wave searches with pulsar timing arrays. This model, BayesEphem, was used to derive ephemeris-robust results in NANOGravs 11-yr stochastic-background search, and it provides a foundation for future searches by NANOGrav and other consortia. The analysis and simulations reported here suggest that ephemeris modeling reduces the gravitational-wave sensitivity of the 11-yr dataset; and that this degeneracy will vanish with improved ephemerides and with the longer pulsar timing datasets that will become available in the near future.
We discuss the theory of pulsar-timing and astrometry probes of a stochastic gravitational-wave background with a recently developed total-angular-momentum (TAM) formalism for cosmological perturbations. We review the formalism, emphasizing in particular the features relevant for this work and describe the observables we consider (i.e. the pulsar redshift and stellar angular displacement). Using the TAM approach, we calculate the angular power spectra for the observables and from them derive angular auto- and cross-correlation functions. We provide the full set of power spectra and correlation functions not only for the standard transverse-traceless propagating degrees of freedom in general relativity, but also for the four additional non-Einsteinian polarizations that may arise in alternative-gravity theories. We discuss how pulsar-timing and astrometry surveys can complement and serve as cross checks to one another and comment on the importance of testing the chirality of the gravitational-wave background as a tool to understand the nature of its sources. A simple rederivation of the power spectra from the plane-wave formalism is provided in an Appendix.
The maximum frequency of gravitational waves (GWs) detectable with traditional pulsar timing methods is set by the Nyquist frequency ($f_{rm{Ny}}$) of the observation. Beyond this frequency, GWs leave no temporal-correlated signals; instead, they appear as white noise in the timing residuals. The variance of the GW-induced white noise is a function of the position of the pulsars relative to the GW source. By observing this unique functional form in the timing data, we propose that we can detect GWs of frequency $>$ $f_{rm{Ny}}$ (super-Nyquist frequency GWs; SNFGWs). We demonstrate the feasibility of the proposed method with simulated timing data. Using a selected dataset from the Parkes Pulsar Timing Array data release 1 and the North American Nanohertz Observatory for Gravitational Waves publicly available datasets, we try to detect the signals from single SNFGW sources. The result is consistent with no GW detection with 65.5% probability. An all-sky map of the sensitivity of the selected pulsar timing array to single SNFGW sources is generated, and the position of the GW source where the selected pulsar timing array is most sensitive to is $lambda_{rm{s}}=-0.82$, $beta_{rm{s}}=-1.03$ (rad); the corresponding minimum GW strain is $h=6.31times10^{-11}$ at $f=1times10^{-5}$ Hz.
We present the sensitivity of the Parkes Pulsar Timing Array to gravitational waves emitted by individual super-massive black-hole binary systems in the early phases of coalescing at the cores of merged galaxies. Our analysis includes a detailed study of the effects of fitting a pulsar timing model to non-white timing residuals. Pulsar timing is sensitive at nanoHertz frequencies and hence complementary to LIGO and LISA. We place a sky-averaged constraint on the merger rate of nearby ($z < 0.6$) black-hole binaries in the early phases of coalescence with a chirp mass of $10^{10},rmn{M}_odot$ of less than one merger every seven years. The prospects for future gravitational-wave astronomy of this type with the proposed Square Kilometre Array telescope are discussed.
The X-ray Navigation and Autonomous position Verification (XNAV) is tested which use the Crab pulsar under the Space Test Program that use starlight refraction. It provide the way that the spacecraft could autonomously determine its position with respect to an inertial origin. Now we analysis the sensitivity of the exist instrument and the signal process that use radio pulsar navigation and discuss the integrated navigation which use radio pulsar, then give the different navigation mission analysis and design process basically which include the space, the airborne, the ship and the land of the planet or the lunar. Our analysis show that we will have the stability profile (signal-to-noise is 5) that use a 2 meters antenna observe some strong sources of radio pulsar in 36 minutes which based on the todays technology. So the pulsar navigation can give the continuous position in deep space, hat means we can freedom fly successfully in the solar system use celestial navigation that include pulsar and traditional star sensor. It also can less or abolish the dependence to Global Navigation Satellite System (GNSS) which include GPS, GRONSS, Galileo and BeiDou et al.
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