European Pulsar Timing Array Janssen, G H; Stappers, B W; Kramer, M ...
40 Years of Pulsars: Millisecond Pulsars, Magnetars and More (AIP Conference Proceedings Volume 983),
01/2008, Volume:
983
Journal Article, Conference Proceeding
Peer reviewed
Open access
The European Pulsar Timing Array is a collaboration that has recently been formed between the five major radio observatories in Europe: Jodrell Bank, Effelsberg, Westerbork, Nancay and Sardinia. ...Together we work towards detecting gravitational waves. We combine the individual strengths of all the different observatories to obtain improved results. We give a short introduction on the partners, goals and instrumentation of this collaboration. Besides gravitational wave detection, the EPTA collaboration is sharing data to optimize timing on, for example, millisecond binary pulsars. We present some recent results of combining datasets of the four telescopes now in use for the EPTA.
Summary of session C1: pulsar timing arrays Shannon, R. M.; Chamberlin, S.; Cornish, N. J. ...
General relativity and gravitation,
08/2014, Volume:
46, Issue:
8
Journal Article
Peer reviewed
This paper summarizes parallel session C1:
Pulsar Timing Arrays
of the Amaldi10/GR20 Meeting held in Warsaw, Poland in July 2013. The session showcased recent results from pulsar timing array ...collaborations, advances in modelling the gravitational-wave signal, and new methods to search for and characterize gravitational waves in pulsar timing array observations.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Millisecond pulsars (MSPs) are known as highly stable celestial clocks. Nevertheless, recent studies have revealed the unstable nature of their integrated pulse profiles, which may limit the ...achievable pulsar timing precision. In this paper, we present a case study on the pulse profile variability of PSR J1022+1001. We have detected approximately 14,000 sub-pulses (components of single pulses) in 35-hr long observations, mostly located at the trailing component of the integrated profile. Their flux densities and fractional polarisation suggest that they represent the bright end of the energy distribution in ordinary emission mode and are not giant pulses. The occurrence of sub-pulses from the leading and trailing components of the integrated profile is shown to be correlated. For sub-pulses from the latter, a preferred pulse width of approximately 0.25 ms has been found. Using simultaneous observations from the Effelsberg 100-m telescope and the Westerbork Synthesis Radio Telescope, we have found that the integrated profile varies on a timescale of a few tens of minutes. We show that improper polarisation calibration and diffractive scintillation cannot be the sole reason for the observed instability. In addition, we demonstrate that timing residuals generated from averages of the detected sub-pulses are dominated by phase jitter, and place an upper limit of ~700 ns for jitter noise based on continuous 1-min integrations.
We report on the high-precision timing of 42 radio millisecond pulsars (MSPs) observed by the European Pulsar Timing Array (EPTA). This EPTA Data Release 1.0 extends up to mid-2014 and baselines ...range from 7-18 years. It forms the basis for the stochastic gravitational-wave background, anisotropic background, and continuous-wave limits recently presented by the EPTA elsewhere. The Bayesian timing analysis performed with TempoNest yields the detection of several new parameters: seven parallaxes, nine proper motions and, in the case of six binary pulsars, an apparent change of the semi-major axis. We find the NE2001 Galactic electron density model to be a better match to our parallax distances (after correction from the Lutz-Kelker bias) than the M2 and M3 models by Schnitzeler (2012). However, we measure an average uncertainty of 80\% (fractional) for NE2001, three times larger than what is typically assumed in the literature. We revisit the transverse velocity distribution for a set of 19 isolated and 57 binary MSPs and find no statistical difference between these two populations. We detect Shapiro delay in the timing residuals of PSRs J1600\(-\)3053 and J1918\(-\)0642, implying pulsar and companion masses \(m_p=1.22_{-0.35}^{+0.5} \text{M}_{\odot}\), \(m_c = 0.21_{-0.04}^{+0.06} \text{M}_{\odot }\) and \(m_p=1.25_{-0.4}^{+0.6} \text{M}_{\odot}\), \(m_c = 0.23_{-0.05}^{+0.07} \text{M}_{\odot }\), respectively. Finally, we use the measurement of the orbital period derivative to set a stringent constraint on the distance to PSRs J1012\(+\)5307 and J1909\(-\)3744, and set limits on the longitude of ascending node through the search of the annual-orbital parallax for PSRs J1600\(-\)3053 and J1909\(-\)3744.
The sensitivity of Pulsar Timing Arrays to gravitational waves depends on the noise present in the individual pulsar timing data. Noise may be either intrinsic or extrinsic to the pulsar. Intrinsic ...sources of noise will include rotational instabilities, for example. Extrinsic sources of noise include contributions from physical processes which are not sufficiently well modelled, for example, dispersion and scattering effects, analysis errors and instrumental instabilities. We present the results from a noise analysis for 42 millisecond pulsars (MSPs) observed with the European Pulsar Timing Array. For characterising the low-frequency, stochastic and achromatic noise component, or "timing noise", we employ two methods, based on Bayesian and frequentist statistics. For 25 MSPs, we achieve statistically significant measurements of their timing noise parameters and find that the two methods give consistent results. For the remaining 17 MSPs, we place upper limits on the timing noise amplitude at the 95% confidence level. We additionally place an upper limit on the contribution to the pulsar noise budget from errors in the reference terrestrial time standards (below 1%), and we find evidence for a noise component which is present only in the data of one of the four used telescopes. Finally, we estimate that the timing noise of individual pulsars reduces the sensitivity of this data set to an isotropic, stochastic GW background by a factor of >9.1 and by a factor of >2.3 for continuous GWs from resolvable, inspiralling supermassive black-hole binaries with circular orbits.
We present upper limits on the X-ray emission for three neutron stars. For PSR J1840\(-\)1419, with a characteristic age of 16.5 Myr, we calculate a blackbody temperature upper limit (at 99% ...confidence) of \(kT_{\mathrm{bb}}^{\infty}<24^{+17}_{-10}\) eV, making this one of the coolest neutron stars known. PSRs J1814\(-\)1744 and J1847\(-\)0130 are both high magnetic field pulsars, with inferred surface dipole magnetic field strengths of \(5.5\times10^{13}\) and \(9.4\times10^{13}\) G, respectively. Our temperature upper limits for these stars are \(kT_{\mathrm{bb}}^{\infty}<123^{+20}_{-33}\) eV and \(kT_{\mathrm{bb}}^{\infty}<115^{+16}_{-33}\) eV, showing that these high magnetic field pulsars are not significantly hotter than those with lower magnetic fields. Finally, we put these limits into context by summarizing all temperature measurements and limits for rotation-driven neutron stars.
The paucity of observed supermassive black hole binaries (SMBHBs) may imply that the gravitational wave background (GWB) from this population is anisotropic, rendering existing analyses sub-optimal. ...We present the first constraints on the angular distribution of a nanohertz stochastic GWB from circular, inspiral-driven SMBHBs using the \(2015\) European Pulsar Timing Array data Desvignes et al. (in prep.). Our analysis of the GWB in the \(\sim 2 - 90\) nHz band shows consistency with isotropy, with the strain amplitude in \(l>0\) spherical harmonic multipoles \(\lesssim 40\%\) of the monopole value. We expect that these more general techniques will become standard tools to probe the angular distribution of source populations.
Millisecond pulsars (MSPs) have been studied in detail since their discovery in 1982. The integrated pulse profiles of MSPs appear to be stable, which enables precision monitoring of the pulse times ...of arrival (TOAs). However, for individual pulses the shape and arrival phase can vary dramatically, which is known as pulse jitter. In this paper, we investigate the stability of integrated pulse profiles for 5 MSPs, and estimate the amount of jitter for PSR J0437-4715. We do not detect intrinsic profile shape variation based on integration times from ~10 to ~100 s with the provided instrumental sensitivity. For PSR J0437-4715 we calculate the jitter parameter to be f_J=0.067+-0.002, and demonstrate that the result is not significantly affected by instrumental TOA uncertainties. Jitter noise is also found to be independent of observing frequency and bandwidth around 1.4 GHz on frequency scales of <100 MHz, which supports the idea that pulses within narrow frequency scale are equally jittered. In addition, we point out that pulse jitter would limit TOA calculation for the timing observations with future telescopes like the Square Kilometre Array and the Five hundred metre Aperture Spherical Telescope. A quantitative understanding of pulse profile stability and the contribution of jitter would enable improved TOA calculations, which are essential for the ongoing endeavours in pulsar timing, such as the detection of the stochastic gravitational wave background.
Pulsar timing observations have revealed companions to neutron stars that include other neutron stars, white dwarfs, main-sequence stars, and planets. We demonstrate that the correlated and ...apparently stochastic residual times of arrival from the millisecond pulsar B1937+21 are consistent with the signature of an asteroid belt having a total mass less than approximately 0.05 Earth masses. Unlike the solar system's asteroid belt, the best fit pulsar asteroid belt extends over a wide range of radii, consistent with the absence of any shepherding companions. We suggest that any pulsar that has undergone accretion-driven spin-up and subsequently evaporated its companion may harbor orbiting asteroid mass objects. The resulting timing variations may fundamentally limit the timing precision of some of the other millisecond pulsars. Observational tests of the asteroid belt model include identifying periodicities from individual asteroids, which are difficult; testing for statistical stationarity that become possible when observations are conducted over a longer observing span; and searching for reflected radio emission.
Direct detection of low-frequency gravitational waves (\(10^{-9} - 10^{-8}\) Hz) is the main goal of pulsar timing array (PTA) projects. One of the main targets for the PTAs is to measure the ...stochastic background of gravitational waves (GWB) whose characteristic strain is expected to approximately follow a power-law of the form \(h_c(f)=A (f/\hbox{yr}^{-1})^{\alpha}\), where \(f\) is the gravitational-wave frequency. In this paper we use the current data from the European PTA to determine an upper limit on the GWB amplitude \(A\) as a function of the unknown spectral slope \(\alpha\) with a Bayesian algorithm, by modelling the GWB as a random Gaussian process. For the case \(\alpha=-2/3\), which is expected if the GWB is produced by supermassive black-hole binaries, we obtain a 95% confidence upper limit on \(A\) of \(6\times 10^{-15}\), which is 1.8 times lower than the 95% confidence GWB limit obtained by the Parkes PTA in 2006. Our approach to the data analysis incorporates the multi-telescope nature of the European PTA and thus can serve as a useful template for future intercontinental PTA collaborations.
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