post-Keplerian Parameters Research Articles

Post-Keplerian parameter to test gravitomagnetic effects in binary pulsar systems

We study the pulsar timing, focusing on the time delay induced by the gravitational field of the binary systems. In particular, we study the gravitomagnetic correction to the Shapiro time delay in terms of Keplerian and post-Keplerian parameters, and we introduce a new post-Keplerian parameter which is related to the intrinsic angular momentum of the stars. Furthermore, we evaluate the magnitude of these effects for the binary pulsar systems known so far. The expected magnitude is indeed small, but the effect is important per se.

Green Bank Telescope Discovery of Two Binary Millisecond Pulsars in the Globular Cluster M30

We report the discovery of two binary millisecond pulsars in the core-collapsed globular cluster M30 using the Green Bank Telescope (GBT) at 20 cm. PSR J2140-2310A (M30A) is an eclipsing 11 ms pulsar in a 4 hr circular orbit, and PSR J2140-23B (M30B) is a 13 ms pulsar in an as yet undetermined but most likely highly eccentric (e > 0.5) and relativistic orbit. Timing observations of M30A with a 20 month baseline have provided precise determinations of the pulsar's position (within 4'' of the optical centroid of the cluster) and spin and orbital parameters, which constrain the mass of the companion star to be m2 ≳ 0.1 M☉. The position of M30A is coincident with a possible thermal X-ray point source found in archival Chandra data, which is most likely caused by emission from hot polar caps on the neutron star. In addition, there is a faint (V555 ~ 23.8) star visible in archival Hubble Space Telescope (HST) F555W data that may be the companion to the pulsar. Eclipses of the pulsed radio emission from M30A by the ionized wind from the compact companion star show a frequency-dependent duration (∝ν-α with α ~ 0.4-0.5) and delay the pulse arrival times near eclipse ingress and egress by up to 2-3 ms. Future observations of M30 may allow both the measurement of post-Keplerian orbital parameters from M30B and the detection of new pulsars through the effects of strong diffractive scintillation.

Timing results for the binary millisecond pulsar J1640+2224 obtained on the RT-64 radio telescope in Kalyazin

We present the timing results for the binary millisecond pulsar J1640+2224 obtained with the RT-64 radio telescope (TNA-1500, Special Design Bureau, Moscow Power Engineering Institute) at the Kalyazin Observatory (Astrospace Center of the Lebedev Institute of Physics) in 1997–2002. We obtained Keplerian and post-Keplerian parameters of the binary system, which allowed us to estimate an upper limit for the energy density of the stochastic gravitational-wave background radiation at very low frequencies.

Recent Observations of PSR B1534+12

We present the results of recent Arecibo observations of the relativistic double-neutron-star binary PSR B1534+12. The timing solution includes measurements of five post-Keplerian orbital parameters, whose values agree well with the predictions of general relativity. The observations show that the pulse profile is evolving secularly at both 1400 MHz and 430 MHz. This effect is similar to that seen in PSR B1913+16, and is almost certainly due to general relativistic precession of the pulsar's spin axis. We also present high-quality polarimetric profiles at both observing frequencies.

Binary Pulsar Tests of General Relativity in the Presence of Low-Frequency Noise

AbstractThe influence of the low-frequency timing noise on the precision of measurements of the Keplerian and post-Keplerian orbital parameters in binary pulsars is studied. Fundamental limits on the accuracy of tests of alternative theories of gravity in the strong-field regime are established. The gravitational low-frequency timing noise formed by an ensemble of binary stars is briefly discussed.

Post‐Newtonian Theory for Precision Doppler Measurements of Binary Star Orbits

The determination of velocities of stars from precise Doppler measurements is described here using a relativistic theory of astronomical reference frames to determine the Keplerian and post-Keplerian parameters of binary systems. Seven reference frames are introduced: (1) the proper frame of a particle emitting light, (2) the star-centered reference frame, (3) the barycentric frame of the binary, (4) the barycentric frame of the Galaxy, (5) the barycentric frame of the solar system, (6) the geocentric frame, and (7) the topocentric frame of observer at the Earth. We apply successive Lorentz transformations and the relativistic equation of light propagation to establish the exact treatment of Doppler effect in binary systems both in special and general relativity theories. As a result, the Doppler shift is a sum of (1) linear in c-1 terms, which include the ordinary Doppler effect and its variation due to the secular radial acceleration of the binary with respect to observer; (2) terms proportional to c-2, which include the contributions from the quadratic Doppler effect caused by the relative motion of binary star with respect to the solar system, the motion of the particle emitting light and diurnal rotational motion of observer, orbital motion of the star around the binary's barycenter, and the orbital motion of the Earth; and (3) terms proportional to c-2, which include the contributions from redshifts due to fields of the star, the star's companion, the Galaxy, the solar system, and the Earth. After parameterization of the binary's orbit, we find that the presence of periodically changing terms in the Doppler shift enables us to disentangle different terms and measure, along with the well-known Keplerian parameters of the binary, four additional post-Keplerian parameters, which characterize (1) the relativistic advance of the periastron; (2) a combination of the quadratic Doppler and shifts associated with the orbital motion of the primary relative to the binary's barycenter and the companion's field, respectively; (3) the amplitude of the gravitational lensing contribution to the Doppler shift; and (4) the usual inclination angle of the binary's orbit, i. We briefly discuss the feasibility of practical implementation of these theoretical results, which crucially depends on further progress in the technique of precision Doppler measurements.

Measurement of Relativistic Orbital Decay in the PSR B1534+12 Binary System

We have made timing observations of binary pulsar PSR B1534+12 with radio telescopes at Arecibo, Green Bank, and Jodrell Bank. By combining our new observations with data collected up to seven years earlier, we obtain a significantly improved solution for the astrometric, spin, and orbital parameters of the system. For the first time in any binary pulsar system, no fewer than five relativistic or orbital parameters are measurable with useful accuracies in a theory-independent way. We find the orbital period of the system to be decreasing at a rate close to that expected from gravitational radiation damping, according to general relativity, although the precision of this test is limited to about 15% by the otherwise poorly known distance to the pulsar. The remaining post-Keplerian parameters are all consistent with one another and all but one of them have fractional accuracies better than 1%. By assuming that general relativity is the correct theory of gravity, at least to the accuracy demanded by this experiment, we find the masses of the pulsar and companion star each to be 1.339+-0.003 Msun and the system's distance to be d = 1.1+-0.2 kpc, marginally larger than the d ~ 0.7 kpc estimated from the dispersion measure. The increased distance reduces estimates of the projected rate of coalescence of double neutron-star systems in the universe, a quantity of considerable interest for experiments with terrestrial gravitational wave detectors such as LIGO.

Strong-field tests of relativistic gravity and binary pulsars.

Observations of pulsars in gravitationally bound binary systems provide a unique opportunity for testing the strong-field regime of relativistic gravity. We present a detailed account of the parametrized (PPK) formalism, a general phenomenological framework designed to extract the maximum possible information from pulsar timing and pulse-structure data. The PPK approach allows dynamical information to be obtained from the data in a theory-independent way, and encoded in a certain number of fitted post-Keplerian parameters. We show that as many as 19 such parameters can be measured, under favorable conditions, giving access to 15 possible tests of relativistic gravity. We isolate and quantify the theoretical content of these tests by deriving, within the framework of generic boost-invariant theories, expressions linking the phenomenological parameters to the inertial masses of the pulsar and its companion, and to the polar angles of the spin axis of the pulsar. The prospects for extracting some of these tests from observations of known or yet-to-be-discovered binary pulsars is quantitatively assessed through numerical simulations. We show that the recently discovered binary pulsar PSR 1534+12 should, with presently available data, give access to two new strong-field tests of relativistic gravity, if the data are analyzed in the phenomenological way emphasized in this paper. Moreover, in the long run, the first-discovered binary pulsar, PSR 1913+16, could give access to three strong-field tests, beyond the presently obtained $\stackrel{\ifmmode \dot{}\else \.{}\fi{}}{\ensuremath{\omega}}\ensuremath{-}\ensuremath{\gamma}\ensuremath{-}{\stackrel{\ifmmode \dot{}\else \.{}\fi{}}{P}}_{b}$ test. Finally, we show how, by combining the PPK approach with the predictions of a rather generic class of tensor-biscalar theories, one can bring together tests based on observations of several different pulsars. We illustrate how such a combination of independent tests can lead to very tight quantitative constraints on possible strong-field deviations from the correct theory of gravity.

Further experimental tests of relativistic gravity using the binary pulsar PSR 1913 + 16

Fourteen-year observations of the binary pulsar PSR 1913 + 16 provided data consistent with a straightforward model allowing for the motion of the earth, special and general relativistic effects within the solar system, dispersive propagation in the interstellar medium, relativistic motion of the pulsar in its orbit, and deterministic spin-down behavior of the pulsar itself. The results indicate that at the present level of precision, the PSR 1913 + 16 can be modeled dynamically as a pair of orbiting point masses. Five Keplerian and five post-Keplerian orbital parameters are therefore mostly determined with remarkably high precision. The masses of the pulsar and its companion are determined to be m1 = 1.442 + or - 0.003 and m2 = 1.386 + or - 0.003 times the mass of the sun, respectively, and the orbit is found to be decaying at a rate equal to 1.01 + or - 0.01 times the general relativistic prediction for gravitational damping. The results represent the first experimental tests of gravitation theory not restricted to the weak-field, slow-motion limit in which nonlinearities and radiation effects are negligible. Excellent agreement between observation and theory indicates conclusively that gravitational radiation exists, at the level predicted by general relativity.more » 70 refs.« less