S. Anderson

Predictions for the Rates of Compact Binary Coalescences Observable by Ground-based Gravitational-wave Detectors

We present an up-to-date, comprehensive summary of the rates for all types of compact binary coalescence sources detectable by the initial and advanced versions of the ground-based gravitational-wave detectors LIGO and Virgo. Astrophysical estimates for compact-binary coalescence rates depend on a number of assumptions and unknown model parameters and are still uncertain. The most confident among these estimates are the rate predictions for coalescing binary neutron stars which are based on extrapolations from observed binary pulsars in our galaxy. These yield a likely coalescence rate of 100 Myr−1 per Milky Way Equivalent Galaxy (MWEG), although the rate could plausibly range from 1 Myr−1 MWEG−1 to 1000 Myr−1 MWEG−1 (Kalogera et al 2004 Astrophys. J. 601 L179; Kalogera et al 2004 Astrophys. J. 614 L137 (erratum)). We convert coalescence rates into detection rates based on data from the LIGO S5 and Virgo VSR2 science runs and projected sensitivities for our advanced detectors. Using the detector sensitivities derived from these data, we find a likely detection rate of 0.02 per year for Initial LIGO–Virgo interferometers, with a plausible range between 2 × 10−4 and 0.2 per year. The likely binary neutron–star detection rate for the Advanced LIGO–Virgo network increases to 40 events per year, with a range between 0.4 and 400 per year.

A test of general relativity from the three-dimensional orbital geometry of a binary pulsar

Binary pulsars provide an excellent system for testing general relativity because of their intrinsic rotational stability and the precision with which radio observations can be used to determine their orbital dynamics. Measurements of the rate of orbital decay of two pulsars have been shown to be consistent with the emission of gravitational waves as predicted by general relativity, but independent verification was not possible. Such verification can in principle be obtained by determining the orbital inclination in a binary pulsar system using only classical geometrical constraints. This would permit a measurement of the expected retardation of the pulse signal arising from the general relativistic curvature of space-time in the vicinity of the companion object (the ‘Shapiro delay’). Here we report high-precision radio observations of the binary millisecond pulsar PSR J0437-4715, which establish the three-dimensional structure of its orbit. We see the Shapiro delay predicted by general relativity, and we determine the mass of the neutron star and its white dwarf companion. The determination of such masses is necessary in order to understand the origin and evolution of neutron stars.

Implementation and testing of the first prompt search for gravitational wave transients with electromagnetic counterparts

Aims. A transient astrophysical event observed in both gravitational wave (GW) and electromagnetic (EM) channels would yield rich scientific rewards. A first program initiating EM follow-ups to possible transient GW events has been developed and exercised by the LIGO and Virgo community in association with several partners. In this paper, we describe and evaluate the methods used to promptly identify and localize GW event candidates and to request images of targeted sky locations. Methods. During two observing periods (Dec. 17, 2009 to Jan. 8, 2010 and Sep. 2 to Oct. 20, 2010), a low-latency analysis pipeline was used to identify GW event candidates and to reconstruct maps of possible sky locations. A catalog of nearby galaxies and Milky Way globular clusters was used to select the most promising sky positions to be imaged, and this directional information was delivered to EM observatories with time lags of about thirty minutes. A Monte Carlo simulation has been used to evaluate the low-latency GW pipelines ability to reconstruct source positions correctly. Results. For signals near the detection threshold, our low-latency algorithms often localized simulated GW burst signals to tens of square degrees, while neutron star/neutron star inspirals and neutron star/black hole inspirals were localized to a few hundred square degrees. Localization precision improves for moderately stronger signals. The correct sky location of signals well above threshold and originating from nearby galaxies may be observed with similar to 50% or better probability with a few pointings of wide-field telescopes.Aims. A transient astrophysical event observed in both gravitational wave (GW) and electromagnetic (EM) channels would yield rich scientific rewards. A first program initiating EM follow-ups to possible transient GW events has been developed and exercised by the LIGO and Virgo community in association with several partners. In this paper, we describe and evaluate the methods used to promptly identify and localize GW event candidates and to request images of targeted sky locations. Methods. During two observing periods (Dec 17 2009 to Jan 8 2010 and Sep 2 to Oct 20 2010), a low-latency analysis pipeline was used to identify GW event candidates and to reconstruct maps of possible sky locations. A catalog of nearby galaxies and Milky Way globular clusters was used to select the most promising sky positions to be imaged, and this directional information was delivered to EM observatories with time lags of about thirty minutes. A Monte Carlo simulation has been used to evaluate the low-latency GW pipelines ability to reconstruct source positions correctly. Results. For signals near the detection threshold, our low-latency algorithms often localized simulated GW burst signals to tens of square degrees, while neutron star/neutron star inspirals and neutron star/black hole inspirals were localized to a few hundred square degrees. Localization precision improves for moderately stronger signals. The correct sky location of signals well above threshold and originating from nearby galaxies may be observed with ~50% or better probability with a few pointings of wide-field telescopes.

Measurement of Orbital Decay in the Double Neutron Star Binary PSR B2127+11C

We report the direct measurement of orbital period decay in the double neutron star pulsar system PSR B2127+11C in the globular cluster M15 at the rate of (-3.95 ± 0.13) × 10-12, consistent with the prediction of general relativity at the ~3% level. We find the pulsar mass to be mp = 1.358 ± 0.010 M☉ and the companion mass mc = 1.354 ± 0.010 M☉. We also report long-term pulse timing results for the pulsars PSR B2127+11A and PSR B2127+11B, including confirmation of the cluster proper motion.

Search for gravitational-wave bursts associated with gamma-ray bursts using data from LIGO science run 5 and VIRGO science run 1.

We present the results of a search for gravitational-wave bursts associated with 137 gamma-ray bursts (GRBs) that were detected by satellite-based gamma-ray experiments during the fifth LIGO science run and first Virgo science run. The data used in this analysis were collected from 2005 November 4 to 2007 October 1, and most of the GRB triggers were from the Swift satellite. The search uses a coherent network analysis method that takes into account the different locations and orientations of the interferometers at the three LIGO-Virgo sites. We find no evidence for gravitational-wave burst signals associated with this sample of GRBs. Using simulated short-duration (<1 s) waveforms, we set upper limits on the amplitude of gravitational waves associated with each GRB. We also place lower bounds on the distance to each GRB under the assumption of a fixed energy emission in gravitational waves, with typical limits of D ~ 15 Mpc (E_GW^iso / 0.01 M_o c^2)^1/2 for emission at frequencies around 150 Hz, where the LIGO-Virgo detector network has best sensitivity. We present astrophysical interpretations and implications of these results, and prospects for corresponding searches during future LIGO-Virgo runs.

The Green Bank Telescope Pulsar Spigot

We describe the design, implementation, and usage of a new facility pulsar search and timing instrument for the 100 m Robert C. Byrd Green Bank Telescope (GBT). This instrument, known as the Pulsar Spigot, makes use of the extremely flexible digital correlator at the GBT to perform rapid autocorrelations (as fast as 2.56 μs) across wide bandwidths (up to 800 MHz) with large numbers of lags (up to 4096), using as many as four simultaneous frequency bands. Successful observations using this instrument have been conducted over the past year and have already resulted in a number of newly discovered pulsars and detailed studies of individual pulsars.

The Proper Motion and Parallax of PSR J0437?4715

We report timing results for PSR J0437-4715 obtained using the Australia Telescope National Facilitys Parkes radio telescope and the Caltech correlator. After model fitting, the timing residuals are only ~500 ns, allowing significant measurements of the annual parallax and the secular change in the orientation of the orbit arising from the systems proper motion. These results allow several independent and self-consistent estimates of the pulsars distance, placing it ~30% farther away than the dispersion measure-derived distance. They also place constraints on the mass of the binary companion and the orbital inclination of the system.

First search for gravitational waves from the youngest known neutron star

We present a search for periodic gravitational waves from the neutron star in the supernova remnant Cassiopeia A. The search coherently analyzes data in a 12 day interval taken from the fifth science run of the Laser Interferometer Gravitational-Wave Observatory. It searches gravitational-wave frequencies from 100 to 300 Hz and covers a wide range of first and second frequency derivatives appropriate for the age of the remnant and for different spin-down mechanisms. No gravitational-wave signal was detected. Within the range of search frequencies, we set 95% confidence upper limits of (0.7-1.2) × 10–24 on the intrinsic gravitational-wave strain, (0.4-4) × 10–4 on the equatorial ellipticity of the neutron star, and 0.005-0.14 on the amplitude of r-mode oscillations of the neutron star. These direct upper limits beat indirect limits derived from energy conservation and enter the range of theoretical predictions involving crystalline exotic matter or runaway r-modes. This paper is also the first gravitational-wave search to present upper limits on the r-mode amplitude.

Timing Observations of the 8-Hr Binary Pulsar 2127+11C in the Globular Cluster M15

We present new results are presented on the position and characteristics of the 8 hr binary pulsar 2127 + 11C in the post-core-collapse (PCC) globular cluster M15. Our results indicate that PSR 2127 + 11C has been ejected from the cluster core via a close encounter with another binary system or isolated star. In particular, the position derived from a phase-connected timing solution places the PSR 2127 + 11C system 2.7 pc (projected) from the core, well outside the compact region containing the other four detected pulsars and the X-ray binary system X2127 + 11/AC 211. While PSR 2127 + 11C is likely still bound to the cluster, it is nonetheless probable that other compact binary pulsars have been totally ejected, thereby contributing to the population of field binary pulsars. Timing results from PSR 2127 + 11C also show a relativistic advance of periastron of 4.46 deg yr^(-1), indicating that the total mass of the system is 2.71 M_⊙.

A Cooling Neutron Star in Supernova Remnant G296.5+10.0

We present a ~20 ks Advanced Satellite for Cosmology and Astrophysics (ASCA) observation of the intriguing X-ray source 1E 1207.4-5209. The source is situated near the center of G296.5+10.0, one of the original barrel-shaped supernova remnants (SNRs). ASCA and ROSAT PSPC data are very well described by a blackbody model of temperature kT = 0.28 keV with a foreground absorbing column of NH = 4 × 1020 cm-2 in the range 0.1-10.0 keV. Previous stringent upper limits for optical and radio emission from the source support a cooling neutron star hypothesis. At its likely distance of 2 kpc, the luminosity LX ~ 1033d22 ergs s-1 implies a radiating surface area A ~ 30d22 km2, which is significantly less than the total area of a canonical neutron star. Despite the large number of detected photons, we see no evidence for rotationally induced X-ray pulsations. Surprisingly, no pulsar-like behavior is found in 1E 1207.4-5209, except that a faint radio nebulosity surrounding it may well be a pulsar-powered plerion. We deduce that the neutron star may have been born spinning very slowly (a birth period P ~ 0.5 s) and is a weak pulsar, which strengthens our belief that the observed radiation is indeed due to surface cooling.