118618521
Results of the First IPTA Closed Mock Data Challenge
The 2012 International Pulsar Timing Array (IPTA) Mock Data Challenge (MDC) is designed to test current Gravitational Wave (GW) detection algorithms. Here we will briefly outline two detection algorithms for a stochastic background of gravitational waves, namely, a first-order likelihood method and an optimal statistic method and present our results from the closed MDC data sets.
279355
Time-domain implementation of the optimal cross-correlation statistic for stochastic gravitational-wave background searches in pulsar timing data
Supermassive black hole binaries, cosmic strings, relic gravitational waves from inflation, and first-order phase transitions in the early Universe are expected to contribute to a stochastic background of gravitational waves in the 10^(−9) –10^(−7)  Hz frequency band. Pulsar timing arrays (PTAs) exploit the high-precision timing of radio pulsars to detect signals at such frequencies. Here we present a time-domain implementation of the optimal cross-correlation statistic for stochastic background searches in PTA data. Due to the irregular sampling typical of PTA data as well as the use of a timing model to predict the times of arrival of radio pulses, time-domain methods are better-suited for gravitational-wave data analysis of such data. We present a derivation of the optimal cross-correlation statistic starting from the likelihood function, a method to produce simulated stochastic background signals, and a rigorous derivation of the scaling laws for the signal-to-noise ratio of the cross-correlation statistic in the two relevant PTA regimes: the weak-signal limit where instrumental noise dominates over the gravitational-wave signal at all frequencies, and a second regime where the gravitational-wave signal dominates at the lowest frequencies.
118358917
A Bayesian analysis pipeline for continuous GW sources in the PTA band
The direct detection of gravitational waves (GWs) by pulsar timing arrays (PTAs) is very likely within the next decade. While the stochastic GW background is a promising candidate for detection it is also possible that single resolvable sources may be detectable as well. In this work we will focus on the detection and characterization of single GW sources from supermassive black hole binaries. We introduce a fully Bayesian data analysis pipeline that is meant to carry out a search, characterization, and evaluation phase. This will allow us to rapidly locate the global maxima in parameter space, map out the posterior, and finally weigh the evidence of a GW detection through a Bayes factor. Here we will make use of an adaptive metropolis algorithm and parallel tempering. We test this algorithm on realistic simulated data that are representative of modern PTAs.
124354053
Stochastic and continuous gravitational wave analysis pipelines for pulsar timing array data
2368665
Support for the thermal origin of the pioneer anomaly.
We investigate the possibility that the anomalous acceleration of the Pioneer 10 and 11 spacecraft is due to the recoil force associated with an anisotropic emission of thermal radiation off the vehicles. To this end, relying on the project and spacecraft design documentation, we constructed a comprehensive finite-element thermal model of the two spacecraft. Then, we numerically solve thermal conduction and radiation equations using the actual flight telemetry as boundary conditions. We use the results of this model to evaluate the effect of the thermal recoil force on the Pioneer 10 spacecraft at various heliocentric distances. We found that the magnitude, temporal behavior, and direction of the resulting thermal acceleration are all similar to the properties of the observed anomaly. As a novel element of our investigation, we develop a parametrized model for the thermal recoil force and estimate the coefficients of this model independently from navigational Doppler data. We find no statistically significant difference between the two estimates and conclude that, once the thermal recoil force is properly accounted for, no anomalous acceleration remains.
12088216
Anomalous orbital-energy changes observed during spacecraft flybys of earth.
We report and characterize anomalous orbital-energy changes observed during six Earth flybys by the Galileo, NEAR, Cassini, Rosetta, and MESSENGER spacecraft. These anomalous energy changes are consistent with an empirical prediction formula which is proportional to the total orbital energy per unit mass and which involves the incoming and outgoing geocentric latitudes of the asymptotic spacecraft velocity vectors. We use this formula to predict a potentially detectable flyby velocity increase of less than 1 mm/s for a second Rosetta flyby on November 13, 2007.
10361426
A Scintillating Glass Fiber-Optic Active Target for Vertex Detection and Tracking Applications in High Energy Physics Experiments
A high resolution, fast gateable active target has been developed for Fermilab experiment E687 in order to study charm and beauty particle production and decay in high energy photon and hadron induced processes. The detector consists of a GS1 Cerium scintillating glass fiber-optic target, a multi-stage image intensifier and CCD camera system used in conjunction with a custom-built video data acquisition system. We currently detect ¿ 4 photoelectrons per mm with a resolution per photoelectron of ¿pe < 25¿m.
115466327
Liquids-in-capillaries: New fiber detectors for high energy physics applications
We are developing scintillating-fiber detectors incorporating organic liquid scintillation cocktails in glass capillaries. The organic solvents have high refractive index, making them suitable as core materials for scintillation waveguides. Only one fluorescent dye at high concentration (1%) is utilized in the solution. This ensures that the dominant energy transfer between solvent and solute will be nonradiative, and that fluorescent emission from the dye will be local to the ionization deposition in the material. Hence such structures might be suitable for high resolution tracking devices. Liquid scintillation solutions may also provide advantages in radiation resistance and replaceability. 8 refs., 6 tabs.