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تسجيل مستخدم جديدThe European Pulsar Timing Array: current efforts and a LEAP toward the future
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Robert D. Ferdman
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The European Pulsar Timing Array (EPTA) is a multi-institutional, multi-telescope collaboration, with the goal of using high-precision pulsar timing to directly detect gravitational waves. In this article we discuss the EPTA member telescopes, current achieved timing precision, and near-future goals. We report a preliminary upper limit to the amplitude of a gravitational wave background. We also discuss the Large European Array for Pulsars, in which the five major European telescopes involved in pulsar timing will be combined to provide a coherent array that will give similar sensitivity to the Arecibo radio telescope, and larger sky coverage.
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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 stoch
astic 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$+$5307 and J1909$-$3744, and set limits on the longitude of ascending node through the search of the annual-orbital parallax for PSRs J1600$-$3053 and J1909$-$3744.
We present new limits on an isotropic stochastic gravitational-wave background (GWB) using a six pulsar dataset spanning 18 yr of observations from the 2015 European Pulsar Timing Array data release. Performing a Bayesian analysis, we fit simultaneou
sly for the intrinsic noise parameters for each pulsar, along with common correlated signals including clock, and Solar System ephemeris errors, obtaining a robust 95$%$ upper limit on the dimensionless strain amplitude $A$ of the background of $A<3.0times 10^{-15}$ at a reference frequency of $1mathrm{yr^{-1}}$ and a spectral index of $13/3$, corresponding to a background from inspiralling super-massive black hole binaries, constraining the GW energy density to $Omega_mathrm{gw}(f)h^2 < 1.1times10^{-9}$ at 2.8 nHz. We also present limits on the correlated power spectrum at a series of discrete frequencies, and show that our sensitivity to a fiducial isotropic GWB is highest at a frequency of $sim 5times10^{-9}$~Hz. Finally we discuss the implications of our analysis for the astrophysics of supermassive black hole binaries, and present 95$%$ upper limits on the string tension, $Gmu/c^2$, characterising a background produced by a cosmic string network for a set of possible scenarios, and for a stochastic relic GWB. For a Nambu-Goto field theory cosmic string network, we set a limit $Gmu/c^2<1.3times10^{-7}$, identical to that set by the {it Planck} Collaboration, when combining {it Planck} and high-$ell$ Cosmic Microwave Background data from other experiments. For a stochastic relic background we set a limit of $Omega^mathrm{relic}_mathrm{gw}(f)h^2<1.2 times10^{-9}$, a factor of 9 improvement over the most stringent limits previously set by a pulsar timing array.
The main goal of pulsar timing array experiments is to detect correlated signals such as nanohertz-frequency gravitational waves. Pulsar timing data collected in dense monitoring campaigns can also be used to study the stars themselves, their binary
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An understanding of pulsar timing noise offers the potential to improve the timing precision of a large number of pulsars as well as facilitating our understanding of pulsar magnetospheres. For some sources, timing noise is attributable to a pulsar s
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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 timescale
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