Modeling the uncertainties of solar-system ephemerides for robust gravitational-wave searches with pulsar timing arrays
M. Vallisneri, S. R. Taylor, J. Simon, W. M. Folkner, R. S. Park, C. Cutler, J. A. Ellis, T. J. W. Lazio, S. J. Vigeland, K. Aggarwal, Z. Arzoumanian, P. T. Bak… 展开作者
M. Vallisneri, S. R. Taylor, J. Simon, W. M. Folkner, R. S. Park, C. Cutler, J. A. Ellis, T. J. W. Lazio, S. J. Vigeland, K. Aggarwal, Z. Arzoumanian, P. T. Baker, A. Brazier, P. R. Brook, S. Burke-Spolaor, S. Chatterjee, J. M. Cordes, N. J. Cornish, F. Crawford, H. T. Cromartie, K. Crowter, M. DeCesar, P. B. Demorest, T. Dolch, R. D. Ferdman, E. C. Ferrara, E. Fonseca, N. Garver-Daniels, P. Gentile, D. Good, J. S. Hazboun, A. M. Holgado, E. A. Huerta, K. Islo, R. Jennings, G. Jones, M. L. Jones, D. L. Kaplan, L. Z. Kelley, J. S. Key, M. T. Lam, L. Levin, D. R. Lorimer, J. Luo, R. S. Lynch, D. R. Madison, M. A. McLaughlin, S. T. McWilliams, C. M. F. Mingarelli, C. Ng, D. J. Nice, T. T. Pennucci, N. S. Pol, S. M. Ransom, P. S. Ray, X. Siemens, R. Spiewak, I. H. Stairs, D. R. Stinebring, K. Stovall, J. K. Swiggum, R. van Haasteren, C. A. Witt, W. W. Zhu
备注：
Fixed typo in author list. Code that supports all calculations and figures is available at github.com/nanograv/11yr_stochastic_analysis/tree/master/bayesephem
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 Earth's 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 (Jupiter's orbital elements) most relevant to gravitational-wave searches with pulsar timing arrays. This model, BayesEphem, was used to derive ephemeris-robust results in NANOGrav's 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.
Pulsar positions can be measured with high precision using both pulsar timing methods and very-long-baseline interferometry (VLBI). Pulsar timing positions are referenced to a solar-system ephemeris, whereas VLBI positions are referenced to distant quasars. Here we compare pulsar positions from published VLBI measurements with those obtained from pulsar timing data from the Nanshan and Parkes radio telescopes in order to relate the two reference frames. We find that the timing positions differ significantly from the VLBI positions (and also differ between different ephemerides). A statisticall…
Rapidly-rotating neutron stars are the only candidates for persistent high-frequency gravitational wave emission, for which a targeted search can be performed based on the spin period measured from electromagnetic (e.g. radio and X-ray) observations. The principal factor determining the sensitivity of such searches is the measurement precision of the physical parameters of the system. Neutron stars in X-ray binaries present additional computational demands for searches due to the uncertainty in the binary parameters. We present the results of a pilot study with the goal of improving the measur…
Neutron stars in low-mass X-ray binaries are considered promising candidate sources of continuous gravitational-waves. These neutron stars are typically rotating many hundreds of times a second. The process of accretion can potentially generate and support non-axisymmetric distortions to the compact object, resulting in persistent emission of gravitational-waves. We present a study of existing optical spectroscopic data for Sco X-1, a prime target for continuous gravitational-wave searches, with the aim of providing revised constraints on key orbital parameters required for a directed search w…
Accreting neutron stars in low-mass X-ray binaries (LMXBs) are candidate high-frequency persistent gravitational wave sources. These may be detectable with next generation interferometers such as Advanced LIGO/VIRGO within this decade. However, the search sensitivity is expected to be limited principally by the uncertainty in the binary system parameters. We combine new optical spectroscopy of Cyg X-2 obtained with the Liverpool Telescope (LT) with available historical radial velocity data, which gives us improved orbital parameter uncertainties based on a 44-year baseline. We obtained an impr…
The Five-hundred-meter Aperture Spherical Telescope (FAST) will become one of the world-leading telescopes for pulsar timing array (PTA) research. The primary goals for PTAs are to detect (and subsequently study) ultra-low-frequency gravitational waves, to develop a pulsar-based time standard and to improve solar system planetary ephemerides. FAST will have the sensitivity to observe known pulsars with significantly improved signal-to-noise ratios and will discover a large number of currently unknown pulsars. We describe how FAST will contribute to PTA research and show that jitter- and timing…
We describe several new techniques which accelerate Bayesian searches for continuous gravitational-wave emission from supermassive black-hole binaries using pulsar timing arrays. These techniques mitigate the problematic increase of search-dimensionality with the size of the pulsar array which arises from having to include an extra parameter per pulsar as the array is expanded. This extra parameter corresponds to searching over the phase of the gravitational-wave as it propagates past each pulsar so that we can coherently include the pulsar-term in our search strategies. Our techniques make th…
Precision astrometry is an integral component of successful pulsar timing campaigns. Astrometric parameters are commonly derived by fitting them as parameters of a timing model to a series of pulse times of arrival (TOAs). TOAs measured to microsecond precision over several-year spans can yield position measurements with sub-milliarcsecond precision. However, timing-based astrometry can become biased if a pulsar displays any red spin noise, which can be compared to the red noise signal produced by the stochastic gravitational wave background. We investigate how noise of different spectral type…
Pulsar timing arrays (PTAs) are being used to search for very low frequency gravitational waves. A gravitational wave signal appears in pulsar timing residuals through two components: one independent of and one dependent on the pulsar's distance, called the 'Earth term' (ET) and 'pulsar term' (PT), respectively. The signal of a burst (or transient) gravitational wave source in pulsars' residuals will in general have the Earth and pulsar terms separated by times of the order of the time of flight from the pulsar to the Earth. Therefore, both terms are not observable over a realistic observation…
We present new timing and spectral analyses of PSR J1412+7922 (Calvera) and PSR J1849-0001, which are only seen as pulsars in X-rays, based on observations conducted with the Neutron Star Interior Composition Explorer (NICER). We obtain updated and substantially improved pulse ephemerides compared to previous X-ray studies, as well as spectra that can be well-fit by simple blackbodies and/or a power law. Our refined timing measurements enable deeper searches for pulsations at other wavelengths and sensitive targeted searches by LIGO/Virgo for continuous gravitational waves from these neutron s…
The Targeted Standard Siren Cosmology with Pulsar Timing Arrays
Indian Institute of Science Education and Research Bhopal（印度科学教育研究所博帕尔分校）；Max Planck Institute for Gravitational Physics (Albert Einstein Institute)（马克斯·普朗克引力物理研究所（爱因斯坦研究所））；Leibniz Universität Hannover（汉诺威莱布尼茨大学）
We present the first 2.5 years of data from the MeerKAT Pulsar Timing Array (MPTA), part of MeerTime, a MeerKAT Large Survey Project. The MPTA aims to precisely measure pulse arrival times from an ensemble of 88 pulsars visible from the Southern Hemisphere, with the goal of contributing to the search, detection and study of nanohertz-frequency gravitational waves as part of the International Pulsar Timing Array. This project makes use of the MeerKAT telescope, and operates with a typical observing cadence of two weeks using the L-band receiver that records data from 856-1712 MHz. We provide a …
A pulsar timing array (PTA) refers to a program of regular, high-precision timing observations of a widely distributed array of millisecond pulsars. Here we review the status of the three primary PTA projects and the joint International Pulsar Timing Array project. We discuss current results related to ultra-low-frequency gravitational wave searches and highlight opportunities for the near future.
Red noise and evolving signals: a complete frequentist approach to supermassive black hole binary searches with pulsar timing arrays
Huazhong University of Science and Technology（华中科技大学）；Max Planck Institute for Gravitational Physics (Albert Einstein Institute)（马克斯·普朗克引力物理研究所（爱因斯坦研究所））；Leibniz Universität Hannover（汉诺威莱布尼茨大学）；University of Texas Rio Grande Valley（德克萨斯里奥格兰德河谷大学）；IIT Hyderabad（印度理工学院海德拉巴分校）
We investigate the impact of noise processes on high-precision pulsar timing. Our analysis focuses on the measurability of the second spin frequency derivative $\ddotν$. This $\ddotν$ can be induced by several factors including the radial velocity of a pulsar. We use Bayesian methods to model the pulsar times-of-arrival in the presence of red timing noise and dispersion measure variations, modelling the noise processes as power laws. Using simulated times-of-arrival that both include red noise, dispersion measure variations and non-zero $\ddotν$ values, we find that we are able to recover the …
The Crab nebula pulsar was observed in 2009 January and December with a novel very fast optical photon counter, Iqueye, mounted at the ESO 3.5 m New Technology Telescope. Thanks to the exquisite quality of the Iqueye data, we computed accurate phase coherent timing solutions for the two observing runs and over the entire year 2009. Our statistical uncertainty on the determination of the phase of the main pulse and the rotational period of the pulsar for short (a few days) time intervals are $\approx 1 \, μ$s and ~0.5 ps, respectively. Comparison with the Jodrell Bank radio ephemerides shows th…
One of the primary objectives for Pulsar Timing Arrays (PTAs) is to detect a stochastic background generated by the incoherent superposition of gravitational waves (GWs), in particular from the cosmic population of supermassive black hole binaries. Current stochastic background searches assume that pulsars in a PTA are separated from each other and the Earth by many GW wavelengths. As more millisecond pulsars are discovered and added to PTAs, some may be separated by only a few radiation wavelengths or less, resulting in correlated GW phase changes between close pulsars in the array. Here we i…
The SUrvey for Pulsars and Extragalactic Radio Bursts ran from 2014 April to 2019 August, covering a large fraction of the southern hemisphere at mid- to high-galactic latitudes, and consisting of 9-minute pointings taken with the 20-cm multibeam receiver on the Parkes Radio Telescope. Data up to 2017 September 21 have been searched using standard Fourier techniques, single-pulse searches, and Fast Folding Algorithm searches. We present 19 new discoveries, bringing the total to 27 discoveries in the programme, and we report the results of follow-up timing observations at Parkes for 26 of these…
Any unambiguous detection of a stochastic gravitational wave background by a pulsar timing array will rest on the measurement of a characteristic angular correlation between pulsars. The ability to measure this correlation will depend on the geometry of the array. However, spatially correlated sources of noise, such as errors in the planetary ephemeris or clock errors, can produce false-positive correlations. The severity of this contamination will also depend on the geometry of the array. This paper quantifies these geometric effects with a spherical harmonic analysis of the pulsar timing res…
Pulsar's position, proper motion and parallax are important parameters in timing equations. It is a really challenging work to fit astrometric parameters accurately through pulsar timing, especially for pulsars that show irregular timing properties. As the fast development of related techniques, it is possible to measure astrometric parameters of more and more pulsars in a model$\textrm{-}$independent manner with the Very Long Baseline Interferometry (VLBI). In this work, we select 16 normal pulsars, whose parallax and proper motion have not been successfully fitted with timing observations or…
Pulsars are very stable clocks in space which have many applications to problems in physics and astrophysics. Observations of double-neutron-star binary systems have given the first observational evidence for the existence of gravitational waves (GWs) and shown that Einstein's general theory of relativity is an accurate description of gravitational interactions in the regime of strong gravity. Observations of a large sample of pulsars spread across the celestial sphere forming a "Pulsar Timing Array" (PTA), can in principle enable a positive detection of the GW background in the Galaxy. The Pa…
Pulsar timing array (PTA) experiments are becoming increasingly sensitive to gravitational waves (GWs) in the nanohertz frequency range, where the main astrophysical sources are supermassive black hole binaries (SMBHBs), which are expected to form following galaxy mergers. Some of these individual SMBHBs may power active galactic nuclei, and thus their binary parameters could be obtained electromagnetically, which makes it possible to apply electromagnetic (EM) information to aid the search for a GW signal in PTA data. In this work, we investigate the effects of such an EM-informed search on b…
4U 1323-619 is a low mass X-ray binary system that shows type I X-ray bursts and dips. The most accurate estimation of the orbital period is 2.941923(36) hrs and a distance from the source that is lower than 11 kpc has been proposed. We aim to obtain the orbital ephemeris, the orbital period of the system, as well as its derivative to compare the observed luminosity with that predicted by the theory of secular evolution. We took the advantage of about 26 years of X-ray data and grouped the selected observations when close in time. We folded the light curves and used the timing technique, obtai…
Pulsar timing arrays: the emerging gravitational-wave landscape
Yale University（耶鲁大学）；Flatiron Institute（平顿研究所）；University of Connecticut（康涅狄格大学）；Stony Brook University（石溪大学）；Columbia University（哥伦比亚大学）；Università degli Studi di Padova（帕多瓦大学）
In this paper, we describe the International Pulsar Timing Array second data release, which includes recent pulsar timing data obtained by three regional consortia: the European Pulsar Timing Array, the North American Nanohertz Observatory for Gravitational Waves, and the Parkes Pulsar Timing Array. We analyse and where possible combine high-precision timing data for 65 millisecond pulsars which are regularly observed by these groups. A basic noise analysis, including the processes which are both correlated and uncorrelated in time, provides noise models and timing ephemerides for the pulsars.…
Radio timing observations of millisecond pulsars (MSPs) in support of Fermi LAT observations of the gamma-ray sky enhance the sensitivity of high-energy pulsation searches. With contemporaneous ephemerides we have detected gamma-ray pulsations from PSR B1937+21, the first MSP ever discovered, and B1957+20, the first known black-widow system. The two MSPs share a number of properties: they are energetic and distant compared to other gamma-ray MSPs, and both of them exhibit aligned radio and gamma-ray emission peaks, indicating co-located emission regions in the outer magnetosphere of the pulsar…
The Parkes Pulsar Timing Array (PPTA) project monitors two dozen millisecond pulsars (MSPs) in order to undertake a variety of fundamental physics experiments using the Parkes 64m radio telescope. Since June 2017 we have been undertaking commensal searches for fast radio bursts (FRBs) during the MSP observations. Here, we report the discovery of four FRBs (171209, 180309, 180311 and 180714). The detected events include an FRB with the highest signal-to-noise ratio ever detected at the Parkes observatory, which exhibits unusual spectral properties. All four FRBs are highly polarized. We discuss…
The Argentine Institute of Radio astronomy (IAR) is equipped with two single-dish 30-m radio antennas capable of performing daily observations of pulsars and radio transients in the southern hemisphere at 1.4 GHz. We aim to contribute to pulsar timing studies related to short time-scale interstellar scintillation and searches for sources of continuous gravitational waves. We performed high-cadence (almost daily) and long-duration observations of the bright millisecond pulsar J0437$-$4715 for over a year, gathering more than 700 hours of good-quality data with timing precision better than 1~$μ$…
Highly energetic astrophysical phenomena like supermassive black hole binary (SMBHB) mergers are predicted to emit prodigious amounts of gravitational waves (GWs). An anticipated component of the gravitational waveform known as "memory" is permanent and non-oscillatory. For SMBHB mergers, the memory is created primarily during the most violent moments of the inspiral immediately preceding the final plunge and ring-down when the strongest gravitational fields are at work and the non-linearities of general relativity are most pronounced. The essentially time-domain nature of memory makes it forb…
The rotating radio transients are sporadic pulsars which are difficult to detect through periodicity searches. By using a single-pulse search method, we can discover these sources, measure their periods, and determine timing solutions. Here we introduce our results on six RRATs based on Parkes and Green Bank Telescope(GBT) observations, along with a comparison of the spin-down properties of RRATs and normal pulsars.
Pulsar timing array (PTA) searches for a gravitational-wave background (GWB) typically include time-correlated "red" noise models intrinsic to each pulsar. Using a simple simulated PTA dataset with an injected GWB signal we show that the details of the red noise models used, including the choice of amplitude priors and even which pulsars have red noise, have a striking impact on the GWB statistics, including both upper limits and estimates of the GWB amplitude. We find that the standard use of uniform priors on the red noise amplitude leads to 95% upper limits, as calculated from one-sided Bay…
A Multimessenger Search for the Supermassive Black Hole Binary in 3C 66B with the Parkes Pulsar Timing Array
Max Planck Institute for Gravitational Physics (Albert Einstein Institute)（马克斯·普朗克引力物理研究所（爱因斯坦研究所））；Leibniz Universität Hannover（汉诺威莱布尼茨大学）；International Centre for Radio Astronomy Research, Curtin University（科廷大学国际射电天文研究中心）；Hunan Normal University（湖南师范大学）；Monash University（蒙纳士大学）；Australia Telescope National Facility, CSIRO, Space and Astronomy（澳大利亚望远镜国家设施，CSIRO空间与天文部门）
PSR J0205+6449 is a young rotation-powered pulsar in SNR 3C 58. It is one of only three young (<10,000 year old) pulsars which are so far detected in the radio and the classical X-ray bands, as well as at hard X-rays above 20 keV and at high-energy (>100 MeV) $γ$-rays. The other two young pulsars are the Crab and PSR B1509-58. Our aim is to derive the timing and spectral characteristics of PSR J0205+6449 over the broad X-ray band from ~0.5 to ~270 keV. We used all publicly available RXTE observations of PSR J0205+6449 to first generate accurate ephemerides over the period September 30, 2000 - …
CubeSats Reach the Millisecond X-Ray Domain: Crab Pulsar Timing with SpIRIT/HERMES
University of Trento（特伦托大学）；University of Palermo（巴勒莫大学）；INAF/Osservatorio Astronomico di Trieste（意大利国家天体物理研究所的里雅斯特天文台）；School of Physics, The University of Melbourne（墨尔本大学物理学院）；Dipartimento di Fisica, Università degli Studi di Cagliari（卡利亚里大学物理系）；INAF/IASF Palermo（意大利国家天体物理研究所巴勒莫空间物理学研究所）；INAF/OAS（意大利国家天体物理研究所博洛尼亚天文台）；INFN Sezione di Bologna（意大利国家核物理研究所博洛尼组分所）
Pulsar timing experiments are currently searching for gravitational waves, and this dissertation focuses on the development and study of the pulsar timing residual models used for continuous wave searches. The first goal of this work is to re-present much of the fundamental physics and mathematics concepts behind the calculations and theory used in pulsar timing. While there exist many reference sources in the literature, I try to offer a fully self-contained explanation of the fundamentals of this research which I hope the reader will find helpful. The next goal broadly speaking has been to f…
Gravitational scattering events, in which the path of an interstellar object is deflected by a pulsar or the solar system, give rise to reflex motion which can potentially be detected using pulsar timing. We determine the form of the timing signal expected from a gravitational scattering event, which is ramp-like and resembles the signal produced by a glitch or a gravitational wave burst with memory (BWM), and investigate the prospects for detecting such a signal using a pulsar timing array. The level of timing precision currently achieved for some millisecond pulsars makes it possible to dete…
Ultra-light Dark Matter (ULDM) models are suitable candidates for the cosmological Dark Matter that may leave characteristic imprints in many observables. Among other probes, signatures of ULDM can be searched for in pulsar timing data. In this work we describe the effects of spin-2 ULDM on pulsar timing arrays, extending previous results on lower spins. Spin-2 ULDM is universally coupled to standard matter with dimensionless strength $α$. We estimate that current data could constrain this coupling in the mass range $m\lesssim4\times10^{-22}$ eV at the $10^{-5}$ to $10^{-6}$ level, which is th…
Using the Parkes radio telescope we have carried out deep observations of eleven unassociated gamma-ray sources. Periodicity searches of these data have discovered two millisecond pulsars, PSR J1103-5403 (1FGL J1103.9-5355) and PSR J2241-5236 (1FGL J2241.9-5236), and a long period pulsar, PSR J1604-44 (1FGL J1604.7-4443). In addition we searched for but did not detect any radio pulsations from six gammaray pulsars discovered by the Fermi satellite to a level of - 0.04 mJy (for pulsars with a 10% duty cycle). Timing of the millisecond pulsar PSR J1103-5403 has shown that its position is 9' from…
A joint MeerKAT and Parkes view of Omega Centauri: New TRAPUM Searches and Pulsar Timing
INAF – Osservatorio Astronomico di Cagliari（意大利国家天体物理研究所卡利亚里天文台）；Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文研究所）；Australia Telescope National Facility, CSIRO（CSIRO澳大利亚望远镜国家设施）；School of Science, Western Sydney University（西悉尼大学理学院）；Space Science Division, Naval Research Laboratory（海军研究实验室空间科学部）；South African Radio Astronomy Observatory（南非射电天文观测站）
We have constructed timing solutions for 81 gamma-ray pulsars covering more than five years of Fermi data. The sample includes 37 radio-quiet or radio-faint pulsars which cannot be timed with other telescopes. These timing solutions and the corresponding pulse times of arrival are prerequisites for further study, e.g. phase-resolved spectroscopy or searches for mode switches. Many gamma-ray pulsars are strongly affected by timing noise, and we present a new method for characterizing the noise process and mitigating its effects on other facets of the timing model. We present an analysis of timi…
Systematic errors in searches for nanohertz gravitational waves
Monash University（莫纳什大学）；OzGrav: The ARC Center of Excellence for Gravitational Wave Discovery（引力波发现ARC卓越中心）；CSIRO, Space and Astronomy（CSIRO空间与天文学部）；Swinburne University of Technology（斯威本科技大学）
