Y. Aso

Present status of large-scale cryogenic gravitational wave telescope

The large-scale cryogenic gravitational wave telescope (LCGT) is the future project of the Japanese gravitational wave group. Two sets of 3 km arm length laser interferometric gravitational wave detectors will be built in a tunnel of Kamioka mine in Japan. LCGT will detect chirp waves from binary neutron star coalescence at 240 Mpc away with a S/N of 10. The expected number of detectable events in a year is two or three. To achieve the required sensitivity, several advanced techniques will be employed such as a low-frequency vibration-isolation system, a suspension point interferometer, cryogenic mirrors, a resonant side band extraction method, a high-power laser system and so on. We hope that the beginning of the project will be in 2005 and the observations will start in 2009.

Stabilization of a Fabry–Perot interferometer using a suspension-point interferometer

A suspension-point interferometer (SPI) is an auxiliary interferometer for active vibration isolation, implemented at the suspension points of the mirrors of an interferometric gravitational wave detector. We constructed a prototype Fabry-Perot interferometer equipped with an SPI and observed vibration isolation in both the spectrum and transfer function. The noise spectrum of the main interferometer was reduced by 40 dB below 1 Hz. Transfer function measurements showed that the SPI also produced good vibration suppression above 1 Hz. These results indicate that SPI can improve both the sensitivity and the stability of the interferometer.

Upper limits on gravitational-wave bursts radiated from stellar-core collapses in our galaxy

We present the results of observations with the TAMA300 gravitational-wave detector, targeting burst signals from stellar-core collapse events. We used an excess-power filter to extract gravitational-wave candidates, and developed two methods to reduce fake events caused by non-stationary noises of the detector. These analysis methods were applied to real data from the TAMA300 interferometric gravitational wave detector. We compared the data-processed results with those of a Monte Carlo simulation with an assumed galactic-event distribution model and with burst waveforms expected from numerical simulations of stellar-core collapses, in order to interpret the event candidates from an astronomical viewpoint. We set an upper limit of 5.0 x 10 3 events s -1 on the burst gravitational-wave event rate in our galaxy with a confidence level of 90%.

Analysis for burst gravitational waves with TAMA300 data

We present analysis results of 1000 h of data of TAMA300; the target was short bursts of gravitational waves. In this analysis, we used an excess power filter for signal detection, and time-scale selection of event candidates for non-Gaussian noise rejection. As a result, no evidence of detection was found. We obtained a false-alarm rate of 4 events/h for h ~ 3 × 10−17 gravitational waves. A time-dependence analysis of the event candidates shows that the false alarms were mainly caused by non-Gaussian noises that had originated in seismic disturbances during the daytime. These results show that further improvements in the detector and analysis methods are required for signal detection.

Analysis methods for burst gravitational waves with TAMA data

We describe analysis methods and results for burst gravitational waves with data obtained in the eighth observation run by the TAMA300 detector. In this analysis, we used an excess-power filter for signal detection, and two types of veto for fake-event rejection; one is a time-scale selection of events and the other is a veto with auxiliary information recorded together with the main signal. We generated an event-candidate list with this analysis procedure, which will be used for coincidence analysis with the other detectors.

Methods to characterize non-Gaussian noise in TAMA

We present a data characterization method for the main output signal of the interferometric gravitational-wave detector, in particular targetting at effective detection of burst gravitational waves from stellar core collapse. The time scale of non-Gaussian events is evaluated in this method, and events with longer time scale than real signals are rejected as non-Gaussian noises. As a result of data analysis using 1000 h of real data with the interferometric gravitational-wave detector TAMA300, the false-alarm rate was improved 103 times with this non-Gaussian noise evaluation and rejection method.