Coincidence analysis to search for inspiraling compact binaries using TAMA300 and LISM data

Japanese laser interferometric gravitational wave detectors, TAMA300 and LISM, performed a coincident observation during 2001. We perform a coincidence analysis to search for inspiraling compact binaries. The length of data used for the coincidence analysis is 275 hours when both TAMA300 and LISM detectors are operated simultaneously. TAMA300 and LISM data are analyzed by matched filtering, and candidates for gravitational wave events are obtained. If there is a true gravitational wave signal, it should appear in both data of detectors with consistent waveforms characterized by masses of stars, amplitude of the signal, the coalescence time and so on. We introduce a set of coincidence conditions of the parameters, and search for coincident events. This procedure reduces the number of fake events considerably, by a factor $\sim 10^{-4}$ compared with the number of fake events in single detector analysis. We find that the number of events after imposing the coincidence conditions is consistent with the number of accidental coincidences produced purely by noise. We thus find no evidence of gravitational wave signals. We obtain an upper limit of 0.046 /hours (CL $= 90$) to the Galactic event rate within 1kpc from the Earth. The method used in this paper can be applied straightforwardly to the case of coincidence observations with more than two detectors with arbitrary arm directions.Comment: 28 pages, 17 figures, Replaced with the version to be published in Physical Review

Results of the search for inspiraling compact star binaries from TAMA300's observation in 2000-2004

We analyze the data of TAMA300 detector to search for gravitational waves from inspiraling compact star binaries with masses of the component stars in the range 1-3Msolar. In this analysis, 2705 hours of data, taken during the years 2000-2004, are used for the event search. We combine the results of different observation runs, and obtained a single upper limit on the rate of the coalescence of compact binaries in our Galaxy of 20 per year at a 90% confidence level. In this upper limit, the effect of various systematic errors such like the uncertainty of the background estimation and the calibration of the detector's sensitivity are included.Comment: 8 pages, 4 Postscript figures, uses revtex4.sty The author list was correcte

Observation results by the TAMA300 detector on gravitational wave bursts from stellar-core collapses

We present data-analysis schemes and results of observations with the TAMA300 gravitational-wave detector, targeting burst signals from stellar-core collapse events. In analyses for burst gravitational waves, the detection and fake-reduction schemes are different from well-investigated ones for a chirp-wave analysis, because precise waveform templates are not available. We used an excess-power filter for the extraction of gravitational-wave candidates, and developed two methods for the reduction of fake events caused by non-stationary noises of the detector. These analysis schemes were applied to real data from the TAMA300 interferometric gravitational wave detector. As a result, fake events were reduced by a factor of about 1000 in the best cases. The resultant event candidates were interpreted from an astronomical viewpoint. We set an upper limit of 2.2x10^3 events/sec on the burst gravitational-wave event rate in our Galaxy with a confidence level of 90%. This work sets a milestone and prospects on the search for burst gravitational waves, by establishing an analysis scheme for the observation data from an interferometric gravitational wave detector

Laser Interferometer Systems for Precise Measurements of Ground-Strains

Four extensometers with laser interferometer systems were installed and have been successively operated in the tunnel at the Amagase Crustal Movement Observatory. Two of them (EL-1 and EL-V) are super-invar bar extensometers with laser interferometer systems consisting of simple laser sources, Michelson interferometers and photodetecting equipment with image-sensors. The remaining two components (L-1 and L-2) are laser extensometers with a frequency-stabilized laser source. Using long term continuous records obtained from EL-1 and L-1, which are orientated along the same direction, effects of instrumental and environmental disturbances have been investigated. Secular ground-strains observed with both components are inconsistent with each other. This disagreement is considered to be mainly caused by the effect of slowly increasing pressure in the enclosing pipes of L-1. Non-periodic ground-strains (residual strains obtained by subtracting the mean values of long term drifts and tidal constituents from observed data of EL-1 and L-1) are consistent with each other in the amplitude range of larger than 10^-8. But they are inconsistent in the amplitude range of smaller than 10^-8 because of different effects of instrumental and environmental disturbances. Tidal strain amplitudes obtained from EL-1 are about 27% smaller than those obtained from L-1. The former may be diminished by frictional forces between the super-invar bar and its supporting rollers

Strain Steps and the Dislocation Fault Model

Strain steps associated with earthquakes ranging in magnitude from 3.2 to 7.9 have been observed at the Iwakura, Amagase and Donzurubo Observatories using super-invar bar extensometers. The stability of these instruments for vibration was confirmed by two methods. The amplitude of strain step depends on distance proportionately with R^-2.4, and based on certain assumptions, fault length seems to be related to earthquake magnitude according to following formula: M=2.2 log L -8.4 where L is the fault length in cm. Furthermore, observed values of strain steps associated with earthquakes of comparatively small magnitude (M=3.2～5.6) occurring in the northern part of the Kinki district have been compared with the residual strain fields calculated by F. Press in 1965

Effects of Meteorological and Hydrological Changes on Ground-Strain Measurements

Using continuous records obtained from four extensometers with laser interferometer systems at the Amagase Observatory, effects of meteorological and hydrological changes on ground-strain measurements have been investigated. Seasonal variations with a strain amplitude of the order of 10^-6 have been observed with horizontal and vertical componetns in directions normal to the axis of the observation tunnel over a period of thirteen months. On the other hand, seasonal variations observed with horizontal components along the tunnel are smaller than 1×10^-7. As a possible source of these variations, we consider the hydrological perturbation due to the seasonal variation of the groundwater pressure around the observation tunnel. After removing seasonal variations from observed data of ground-strains, there remain transient variations of the order of 10^-7 in components normal to the tunnel. While, variations of this sort are not found in components along the tunnel. These transient variations cannot be explained by the elastic strains caused by the negative surface-load due to the passage of the typhoon or due to the fluctuation of the water level in a nearby reservoir, but can be explained by the hydrological effect of groundwater pressures in pores of a porous medium under the rapid draw-up or draw-down of the water level of the reservoir

Effects of Local Inhomogeneities on Tidal Strain Measurements

Using continuous records obtained from four extensometers with laser interferometer systems at Amagase, Kyoto Prefecture, we analyzed tidal strains by the least squares method. The result shows that there exist remarkable discrepancies between observed values and theoretically predicted ones for a laterally homogeneous earth model. Amplitude enhancements of tidal strains observed with the horizontal and vertical components in normal directions to the axis of the tunnel are well explained by the cavity effects calculated by two-dimensional finite element techniques for the actual cross-section of the tunnel. After eliminating the cavity effects, observed values were compared with theoretically predicted ones containing the topographic corrections calculated by three-dimensional finite element techniques. As a result, differences of phases between observed and theoretically predicted values are within 5° in any case. Amplitudes of observed tidal strains in the direction along the tunnel are about 15% smaller than predicted values but these differences are comparable to errors inherent in calculations. On the contrary, amplitudes of observed values in the direction across the tunnel are 33～52% larger than the predicted ones. As the most possible source of these differences, we consider the hydrological perturbation caused by fluctuations of the ground-water level around the observation tunnel