We review the expected science performance of the New Gravitational-Wave Observatory (NGO, a.k.a. eLISA), a mission under study by the European Space Agency for launch in the early 2020s. eLISA will survey the low-frequency gravitational-wave sky (from 0.1 mHz to 1 Hz), detecting and characterizing a broad variety of systems and events throughout the Universe, including the coalescences of massive black holes brought together by galaxy mergers; the inspirals of stellar-mass black holes and compact stars into central galactic black holes; several millions of ultra-compact binaries, both detached and mass transferring, in the Galaxy; and possibly unforeseen sources such as the relic gravitational-wave radiation from the early Universe. eLISA's high signal-tonoise measurements will provide new insight into the structure and history of the Universe, and they will test general relativity in its strong-field dynamical regime.
The Global Oscillation Network Group (GONG) project estimates the frequencies, amplitudes, and linewidths of more than 250,000 acoustic resonances of the sun from data sets lasting 36 days. The frequency resolution of a single data set is 0.321 microhertz. For frequencies averaged over the azimuthal order m, the median formal error is 0.044 microhertz, and the associated median fractional error is 1.6 x 10(-5). For a 3-year data set, the fractional error is expected to be 3 x 10(-6). The GONG m-averaged frequency measurements differ from other helioseismic data sets by 0.03 to 0.08 microhertz. The differences arise from a combination of systematic errors, random errors, and possible changes in solar structure.
The baseline design concept for a seismic isolation component of the proposed "Advanced LIGO" detector upgrade has been developed with proofof-principle experiments and with computer models. It consists of a two-stage in-vacuum active isolation platform that is supported by an external hydraulic actuation stage. Construction is underway for prototype testing of a full-scale preliminary design.
The performance of the LISA gravitational wave detector depends critically on limiting spurious accelerations of the fiducial masses. Consequently, the requirements on allowable acceleration levels must be carefully allocated based on estimates of the achievable limits on spurious accelerations from all disturbances. Changes in the allocation of requirements are being considered, and are proposed here. The total spurious acceleration error requirement would remain unchanged, but a few new error sources would be added, and the allocations for some specific error sources would be changed. In support of the recommended revisions in the requirements budget, estimates of plausible acceleration levels for 17 of the main error sources are discussed. In most cases, the formula for calculating the size of the effect is known, but there may be questions about the values of various parameters to use in the estimates. Different possible parameter values have been discussed, and a representative set is presented. Improvements in our knowledge of the various experimental parameters will come from planned experimental and modelling studies, supported by further theoretical work.
We have made high-resolution observations of the Sun in which we identify individual sunquakes and see power from these seismic events being pumped into the resonant modes of vibration of the Sun. A typical event lasts about 5 minutes. We report the physical properties of the events and relate them to theories of the excitation of solar oscillations. We also discuss the local seismic potential of these events.
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