PSR 1913 +16 Research Articles

Evading the Vainshtein Mechanism with Anomalous Gravitational Wave Speed: Constraints on Modified Gravity from Binary Pulsars.

By using observations of the Hulse-Taylor pulsar, we constrain the gravitational wave (GW) speed to the level of 10(-2). We apply this result to scalar-tensor theories that generalize Galileon 4 and 5 models, which display anomalous propagation speed and coupling to matter for GWs. We argue that this effect survives conventional screening due to the persistence of a scalar field gradient inside virialized overdensities, which effectively "pierces" the Vainshtein screening. In specific branches of solutions, our result allows us to directly constrain the cosmological couplings in the effective field theory of dark energy formalism.

DIVISION F COMMISSION 53: EXTRASOLAR PLANETS

The IAU Working Group on Extrasolar Planets (WGESP) was created by the Executive Council as a Working Group of Division III. This decision took place in June 1999, that is only 7 years after the discovery of planets around the pulsar PSR B1257+12 and 4 years after the discovery of 51 Peg b. This working group was renewed for 3 years at the General Assembly in 2003 in Sydney, Australia. It was chaired by Alan Boss from Carnegie Institution of Washington. The WGESP members were Paul Butler, William Hubbard, Philip Ianna, Martin Kürster, Jack Lissauer, Michel Mayor, Karen Meech, Francois Mignard, Alan Penny, Andreas Quirrenbach, Jill Tarter, and Alfred Vidal-Madjar.

OJ287: Post-Newtonian Calculation in Harmonic Coordinate and Pulsar Timing Residual Confirmation* *Supported by National Natural Science Foundation of China under Grant Nos. 11275187, 11421303, and the Strategic Priority Research Program “The Emergence of Cosmological Structures” of the Chinese Academy of Sciences under Grant No. XDB09000000

We calculate and discuss the motion of the binary black hole OJ287 based on Post-Newtonian approximation in a harmonic coordinate. With gravitational waveform obtained, theoretical timing residual of PSR B1855+09 induced by gravitational radiation of OJ287 is presented and compared with observed data, further shows that hypothesis referring to OJ287 as a binary BH system might be proper. The energy flux of gravitational radiation from binary is also provided, from which we find that the flux changes sign successively: ĖN > 0, Ė1PN < 0, Ė2PN > 0, in agreement with the relative signs of forces of each PN order, revealed in the previous work.

1974: the discovery of the first binary pulsar

The 1974 discovery, by Russell A Hulse and Joseph H Taylor, of the first binary pulsar, PSR B1913+16, opened up new possibilities for the study of relativistic gravity. PSR B1913+16, as well as several other binary pulsars, provided direct observational proof that gravity propagates at the velocity of light and has a quadrupolar structure. Binary pulsars also provided accurate tests of the strong-field regime of relativistic gravity. General relativity has passed all of the binary pulsar tests with flying colors. The discovery of binary pulsars also had very important consequences for astrophysics, leading to accurate measurement of neutron star masses, improved understanding of the possible evolution scenarios for the co-evolution of binary stars, and proof of the existence of binary neutron stars emitting gravitational waves for hundreds of millions of years, before coalescing in catastrophic events radiating intense gravitational wave signals, and probably also leading to important emissions of electromagnetic radiation and neutrinos. This article reviews the history of the discovery of the first binary pulsar, and describes both its immediate impact and its longer-term effect on theoretical and experimental studies of relativistic gravity.

OLD NEUTRON STARS AS PROBES OF ISOSPIN-VIOLATING DARK MATTER

Isospin-violating dark matter (IVDM), which couples differently with protons and neutrons, provides a promising mechanism to ameliorate the tension among recent direct detection experiments. Assuming DM is non-interacting bosonic asymmetric IVDM, we investigate how the existence of old neutron stars limits the DM-proton scattering cross-section $\sigma_{\rm p}$, especially the effects of the isospin violating DM-nucleon interactions and the symmetry energy in the equation of state of isospin asymmetric nuclear matter. Our calculations are completely based on general relativity and especially the structure of neutron stars is obtained by solving the Tolman-Oppenheimer-Volkoff equations with nuclear matter equation of state constrained by terrestrial experiments. We find that, by considering the more realistic neutron star model rather than a simple uniform neutron sphere as usual, the $\sigma_{\rm p}$ bounds from old neutron stars can be varied by more than an order of magnitude depending on the specific values of the DM neutron-to-proton coupling ratio $f_{\rm n}/f_{\rm p}$, and they can be further varied by more than a factor of two depending on the density dependence of the symmetry energy. In particular, we demonstrate that the observed nearby isolated old neutron star PSR B1257+12 can set a very strong limit on $\sigma_{\rm p}$ for low-mass DM particles ($ \le 20 \, {\rm GeV}$) that reaches a sensitivity beyond the current best limits from direct detection experiments and disfavors the DM interpretation of previously-reported positive experimental results, including the IVDM.

Pulsar constraints on screened modified gravity

We calculate the rate of energy loss from compact astrophysical objects due to a scalar field in screened modified gravity models of the chameleon, dilaton and symmetron types. The cosmological evolution of the field results in a time-variation of the scalar charge of screened objects, implying the emission of scalar radiation. Focusing on binary objects, this leads to an additional decay in the orbital period complementing that due to the emission of gravitational waves. Using the Hulse–Taylor binary pulsar, the double pulsar PSR J0737–3039 and the pulsar-white dwarf system PSR J1738 + 033, we find a new observational bound on the time variation of the scalar charge of the Earth in the Milky Way. We then translate this into a new bound on the range of the scalar interaction in the Milky Way. Ultimately, we find that pulsar tests are not competitive with current observational constraints.

Preliminary limits of a logarithmic correction to the Newtonian gravitational potential in binary pulsars

We obtain preliminary limits on a logarithmic correction to the Newtonian gravitational potential by using five binary pulsars: PSR J0737−3039, PSR B1534+12, PSR J1756−2251, PSR B1913+16 and PSR B2127+11C. This kind of correction may originate from fundamental frameworks, like string theories, effective models of gravity due to quantum effects and the non-local gravity scheme. We estimate the upper limit of the Tohline-Kuhn-Kruglyak parameter λ and the lower limit of the Fabris-Campos parameter α, which parameterize the correction and are connected to each other by αλ = −1. By analyzing the advances of periastron of these binary pulsars, we find that the preliminary upper limit of α is 0.19 ± 0.14 kpc−1 and the preliminary lower limit of λ is −5.2 ± 3.8 kpc. They are compatible with the bounds based on dynamics of spiral galaxies but quite different from those given by solar system dynamics. These results indicate that this logarithmic correction might be more observable in current timings of binary pulsars than in motions of the solar system.

IMPORTANCE OF TIDES FOR PERIASTRON PRECESSION IN ECCENTRIC NEUTRON STAR-WHITE DWARF BINARIES

Although not nearly as numerous as binaries with two white dwarfs, eccentric neutron star-white dwarf (NS-WD) binaries are important gravitational-wave (GW) sources for the next generation of space-based detectors sensitive to low frequency waves. Here we investigate periastron precession in these sources as a result of general relativistic, tidal, and rotational effects; such precession is expected to be detectable for at least some of the detected binaries of this type. Currently, two eccentric NS-WD binaries are known in the galactic field, PSR J1141-6545 and PSR B2303+46, both of which have orbits too wide to be relevant in their current state to GW observations. However, population synthesis studies predict the existence of a significant Galactic population of such systems. Though small in most of these systems, we find that tidally induced periastron precession becomes important when tides contribute to more than 3% of the total precession rate. For these systems, accounting for tides when analyzing periastron precession rate measurements can improve estimates of the WD component mass inferred and, in some cases, will prevent us from misclassifying the object. However, such systems are rare due to rapid orbital decay. To aid the inclusion of tidal effects when using periastron precession as a mass measurement tool, we derive a function that relates the WD radius and periastron precession constant to the WD mass.

MILLISECOND PULSAR SCINTILLATION STUDIES WITH LOFAR: INITIAL RESULTS

High-precision timing of millisecond pulsars (MSPs) over years to decades is a promising technique for direct detection of gravitational waves at nanohertz frequencies. Time-variable, multi-path scattering in the interstellar medium is a significant source of noise for this detector, particularly as timing precision approaches 10 ns or better for MSPs in the pulsar timing array. For many MSPs the scattering delay above 1 GHz is at the limit of detectability; therefore, we study it at lower frequencies. Using the LOFAR (LOw-Frequency ARray) radio telescope we have analyzed short (5-20 min) observations of three MSPs in order to estimate the scattering delay at 110-190 MHz, where the number of scintles is large and, hence, the statistical uncertainty in the scattering delay is small. We used cyclic spectroscopy, still relatively novel in radio astronomy, on baseband-sampled data to achieve unprecedented frequency resolution while retaining adequate pulse phase resolution. We detected scintillation structure in the spectra of the MSPs PSR B1257+12, PSR J1810+1744, and PSR J2317+1439 with diffractive bandwidths of $6\pm 3$, $2.0\pm 0.3$, and $\sim 7$ kHz, respectively, where the estimate for PSR J2317+1439 is reliable to about a factor of 2. For the brightest of the three pulsars, PSR J1810+1744, we found that the diffractive bandwidth has a power-law behavior $\Delta\nu_d \propto \nu^{\alpha}$, where $\nu$ is the observing frequency and $\alpha = 4.5\pm 0.5$, consistent with a Kolmogorov inhomogeneity spectrum. We conclude that this technique holds promise for monitoring the scattering delay of MSPs with LOFAR and other high-sensitivity, low-frequency arrays like SKA-Low.

The Confrontation between General Relativity and Experiment.

The status of experimental tests of general relativity and of theoretical frameworks for analyzing them is reviewed and updated. Einstein’s equivalence principle (EEP) is well supported by experiments such as the Eötvös experiment, tests of local Lorentz invariance and clock experiments. Ongoing tests of EEP and of the inverse square law are searching for new interactions arising from unification or quantum gravity. Tests of general relativity at the post-Newtonian level have reached high precision, including the light deflection, the Shapiro time delay, the perihelion advance of Mercury, the Nordtvedt effect in lunar motion, and frame-dragging. Gravitational wave damping has been detected in an amount that agrees with general relativity to better than half a percent using the Hulse-Taylor binary pulsar, and a growing family of other binary pulsar systems is yielding new tests, especially of strong-field effects. Current and future tests of relativity will center on strong gravity and gravitational waves.

PULSAR WIND MODEL FOR THE SPIN-DOWN BEHAVIOR OF INTERMITTENT PULSARS

Intermittent pulsars are part-time radio pulsars. They have higher slow down rate in the on state (radio-loud) than in the off state (radio-quiet). This gives the evidence that particle wind may play an important role in pulsar spindown. The effect of particle acceleration is included in modeling the rotational energy loss rate of the neutron star. Applying the pulsar wind model to the three intermittent pulsars (PSR B1931+24, PSR J1841-0500, and PSR J1832+0029), their magnetic field and inclination angle are calculated simultaneously. The theoretical braking indices of intermittent pulsars are also given. In the pulsar wind model, the density of the particle wind can always be the Goldreich-Julian density. This may ensure that different on states of intermittent pulsars are stable. The duty cycle of particle wind can be determined from timing observations. It is consistent with the duty cycle of the on state. Inclination angle and braking index observations of intermittent pulsars may help to test different models of particle acceleration. At present, the inverse Compton scattering induced space charge limited flow with field saturation model can be ruled out.

A COMPREHENSIVE STUDY OF RELATIVISTIC GRAVITY USING PSR B1534+12

We present updated analyses of pulse profiles and their arrival-times from PSR B1534+12, a 37.9-ms radio pulsar in orbit with another neutron star. A high-precision timing model is derived from twenty-two years of timing data, and accounts for all astrophysical processes that systematically affect pulse arrival-times. Five "post-Keplerian" parameters are measured that represent relativistic corrections to the standard Keplerian quantities of the pulsar's binary orbit. These relativistic parameters are then used to test general relativity by comparing the measurements with their predicted values. We conclude that relativity theory is confirmed to within 0.17% of its predictions. Furthermore, we derive the following astrophysical results from our timing analysis: a distance of $d_{\rm GR} = 1.051 \pm 0.005$ kpc to the pulsar-binary system, by relating the "excess" orbital decay to Galactic parameters; evidence for pulse "jitter" in PSR B1534+12 due to short-term magnetospheric activity; and evolution in pulse-dispersion properties. As a secondary study, we also present several analyses on pulse-structure evolution and its connection to relativistic precession of the pulsar's spin axis. The precession-rate measurement yields a value of $\Omega_1^{\rm spin}$ = $0.59^{+0.12}_{-0.08}$ $^{\circ}$/year (68% confidence) that is consistent with expectations, and represents an additional test of relativistic gravity.

The influence of triaxiality and oblateness on the triangular points of double pulsars in the ER3BP

We consider the motion of a test particle around a triaxial primary and an oblate companion orbiting each other in elliptic orbits about their common barycenter in the neighborhood of triangular libration points. The positions and stability of these points are influenced by the triaxiality and oblateness of the primary and secondary, and by the semi-major axis and eccentricity of the orbits. The triangular points are stable for 0<μ<μc; where μ is the mass ratio (μ≤1/2) and μc is the critical mass value influenced by the eccentricity, oblateness, semi major axis and triaxiality factors. The size of the region of stability increases with decreasing values of triaxiality and oblateness. An application of the results obtain to double neutron star binaries results show that the positions and stability of the triangular points of PSR J1518+4904, PSR B1534+12, PSR B1914+16 and PSR B2127+11c are affected by the parameters in the systems’ dynamics.

Gravitational Waves in General Relativity, and in the Hulse-Taylor Pulsar. Supernova Models indicate that the Quantum of Gravitational Radiation is the Neutrino

Gravitational Waves in General Relativity, and in the Hulse-Taylor Pulsar. Supernova Models indicate that the Quantum of Gravitational Radiation is the Neutrino

Predicting the Braking Indices of Nulling and Intermittent Pulsars

The braking index is an important factor when examining the pulsar braking mechanism. Measuring braking indices requires measuring the pulsar period and its first and second derivatives. Among them, the second derivative is easily contaminated by timing noise and an unresolved glitch effect. The absence of data bounding a given transition into (or out of) a radio-on phase is another disadvantage in measuring the second derivatives of intermittent pulsars, as was recently demonstrated by Young and coworkers. But, the observed period first derivatives, in the “on” and “off” states of the intermittent pulsars, give us a possible way to predict their braking indices even though they are hard to observe. In this paper, we will give a simple and useful method to study the braking indices of intermittent pulsars. As an application of our method, we will calculate the possible braking indices of three intermittent pulsars and one nulling pulsar, namely, PSR B1931 + 24, PSR J1841 - 0500, PSR J1832 + 0029 and PSR B0823 + 26, under three different magnetospheric conditions, which include polar cap size variation, charge density variation and the combination of the above two cases. We have found that all the braking indices we predicted are almost within the observed domain. It is concluded that, in a relatively short observation period, in which the variation of the braking index can be ignored, we can accurately predict the braking indices of intermittent pulsars, under a specific magnetosphere model, by using the observed “on” and “off” state period first derivatives.

The Properties of the Neutron Star PSR B2303+46

The properties of the neutron star PSR B2303 + 46 are investigated within the framework of relativistic mean field theory for the baryon octet system through adjusting the hyperon coupling constants. Models for the neutron star B2303+46 are obtained by choosing suitable hyperon coupling constants x_(σh) and x_(ωh), with x_(ρh) being determined by the constituent quark model SU (6) symmetry and the nucleon coupling constants being chosen as the set CZ11. Our results show that the field strengths of the mesons σ, ω, and ρ, the chemical potentials of the neutron and electron, the relative particle number density of the electron, muon, neutron, proton, Λ, Σ, and Ξ, and the pressure and energy density of the neutron star PSR B2303 + 46 all have an uncertain value region, respectively.

TRIGONOMETRIC PARALLAXES OF HIGH MASS STAR FORMING REGIONS: THE STRUCTURE AND KINEMATICS OF THE MILKY WAY

Over 100 trigonometric parallaxes and proper motions for masers associated with young, high-mass stars have been measured with the BeSSeL Survey, a VLBA key science project, the EVN, and the Japanese VERA project. These measurements provide strong evidence for the existence of spiral arms in the Milky Way, accurately locating many arm segments and yielding spiral pitch angles ranging from 7 to 20 degrees. The widths of spiral arms increase with distance from the Galactic center. Fitting axially symmetric models of the Milky Way with the 3-D position and velocity information and conservative priors for the solar and average source peculiar motions, we estimate the distance to the Galactic center, Ro, to be 8.34 +/- 0.16 kpc, a circular rotation speed at the Sun, To, to be 240 +/- 8 km/s, and a rotation curve that is nearly flat (a slope of -0.2 +/- 0.4 km/s/kpc) between Galactocentric radii of 5 and 16 kpc. Assuming a "universal" spiral galaxy form for the rotation curve, we estimate the thin disk scale length to be 2.44 +/- 0.16 kpc. The parameters Ro and To are not highly correlated and are relatively insensitive to different forms of the rotation curve. Adopting a theoretically motivated prior that high-mass star forming regions are in nearly circular Galactic orbits, we estimate a global solar motion component in the direction of Galactic rotation, Vsun = 14.6 +/- 5.0 km/s. While To and Vsun are significantly correlated, the sum of these parameters is well constrained, To + Vsun = 255.2 +/- 5.1 km/s, as is the angular speed of the Sun in its orbit about the Galactic center, (To + Vsun)/Ro = 30.57 +/- 0.43 km/s/kpc. These parameters improve the accuracy of estimates of the accelerations of the Sun and the Hulse-Taylor binary pulsar in their Galactic orbits, significantly reducing the uncertainty in tests of gravitational radiation predicted by general relativity.

Search for 150 MHz radio emission from extrasolar planets in the TIFR GMRT Sky Survey

The ongoing radio continuum TIFR GMRT Sky Survey (TGSS) using the Giant Metrewave Radio Telescope (GMRT) at 150 MHz offers an unprecedented opportunity to undertake a fairly deep search for low-frequency radio emission from nearby extrasolar planets. Currently TGSS images are available for a little over a steradian, encompassing 175 confirmed exoplanetary systems. We have searched for their radio counterparts in the TGSS (150 MHz), supplemented with a search in the NRAO VLA Sky Survey (NVSS) and the VLA FIRST survey at 1.4 GHz. For 171 planetary systems, we find no evidence of radio emission in the TGSS maps, placing a3 σ upper limit between 8.7 mJy and 136 mJy (median ∼24.8 mJy) at 150 MHz. These non-detections include the 55 Cnc system for which we place a 3σ upper limit of 28 mJy at 150 MHz. Nonetheless, for four of the extrasolar planetary systems, we find TGSS radio sources coinciding with or located very close to their coordinates. One of these is 61 Vir: for this system a large radio flux density was predicted in the scenario involving magnetosphere-ionosphere coupling and rotation-induced radio emission. We also found 150 MHz emissions toward HD 86226 and HD 164509, where strong radio emission can be produced by the presence of a massive satellite orbiting a rapidly rotating planet. We also detected 150 MHz emission within a synthesized beam from 1RXS1609 b, a pre-main-sequence star harboring a ∼14 Jupiter mass planet (or a brown dwarf). With a bright X-ray-UV star and a high mass, the planet 1RXS1609 b presents the best characteristics for rotation-induced emissions with high radio power. Deeper high-resolution observations toward these planetary systems are needed to discriminate between the possibilities of background radio-source and radio-loud planets. At 1.4 GHz, radio emission toward the planet-harboring pulsar PSR B1620-26 is detected in the NVSS. Emissions at 1.4 GHz are also detected toward the very-hot-Jupiter WASP-77A b (in the FIRST survey) and the giant planet HD 43197 b in a highly eccentric orbit (in NVSS). We briefly discuss these detections, as well as the non-detection of the vast majority of exoplanets.

Revisiting the border between Newtonian mechanics and General Relativity: The periastron advance

The problem of periastron advance, which is the basis of one of the three classical tests of relativity theory, is revised with respect to both Newtonian mechanics and General Relativity and updated in the light of recent astronomical measurements of binary pulsars. We show that in Newtonian mechanics the addition of a corrective term to Newton’s law of gravitation, consistent with the principles of Newtonian mechanics, leads to the same formula of periastron advance as that used in General Relativity, which proves to be valid in all astronomical cases known, even in the cases of binary pulsars such as PSR B1913+16, PSR J1141-6545 and the so-called double pulsar PSR J0737-3039A and PSR J0737-3039B, which are considered as natural relativity laboratories. Thus, among the relativistic phenomena, the periastron advance is one that can be also understood in Newtonian terms by means of an ad hoc assumption.

On motion around the collinear libration points in the elliptic R3BP with a bigger triaxial primary

We investigate the motion of a test particle in the vicinity of a binary made of a triaxial primary and a spherical companion moving along elliptic orbits about their common barycenter in the neighborhood of collinear libration points. Their positions and stability are found to be affected by the triaxiality of the bigger primary, and by the semi-major axis and the eccentricity of the binary’s orbits as well. The analytic results obtained are applied to binary neutron stars consisting of a bigger triaxial primary and a spherical companion. A numerical analysis shows that the positions of the collinear points of PSR J1518+4904, PSR B1534+12, PSR B1914+16, and PSR B2127+11c are affected by the triaxiality of the bigger primary, and by the eccentricity of the orbits. The stability behavior however remains unchanged: the collinear points remain unstable in the Lyapunov sense.